TABLE OF CONTENTS
Object of Part 2 of the Paper . . 130
Problem consists in study of efiect of twelve variables on cutting speed of tool 135
Cutting speed (20-minute cut) standard by which to measure effect of each variable, with illustration of practical application of standard 137
“Standard speed." Best method for determining value of tools, etc., 138 to 144
False standards in common use. Time tool will last 145
ACTION OF TOOL AND ITS WEAR IN CUTTING METALS
Action of the nose of the tool . . . . 153
Metal torn away, not cut or wedged 153
Analysis of strains in chip and forging 156
Action of cutting edge is that of scraping cutting edge not under heavy pressure 170
Nature of wear on tools depends on whether it has been chiefly caused by heat 175
Three classes of wear (1) heat, (2) heat and friction combined, (3) friction without heat 177
Reason for adopting standard test period of 20 minutes 183
“ Economical” cutting speeds 185
How carbon steel tempered and tools made from old fashioned self-hardening steel wear 189
How modern high-speed tools wear 201
HOW TO MAKE AND RECORD EXPERIMENTS
Art of experimenting defined as determining effict of varying one element while all others are held constant 210
Met al which is to be cut . 213
Experimental lathe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
217
Speed changes on the machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
222
Feeding mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
224
Weight of the machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
226
Best type of experimental lathe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
227
Measuring the cutting speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
230
Measuring the depth of cut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
238
If niformity in the cutting tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
245
Where practicable in experimenting no cuts lighter than 1%; inch depth by 3*; inch feed should be taken . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
252
More time required in preparation than in experimenting . . . . . . . . . . . . . .
254
Recording the details and results of experiments . . . . . . . . . . . . . . . . . . . . . . . . .
257
—i_,_ _ Operator’s daily record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
258
Summary sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
259
Each law and diagram the result of several series of experiments . . . . . . . . . . .
263
PROPER SHAPE FOR STANDARD SHOP ROUGHING TOOLS
A few carefully considered types of tools better than great variety . 268
Standard tools illustrated . . 269
Conflict between the difiercnt objects to be attained in cutting metals which affect the design of standard tools . 271
Elements affecting cutting speed of tools in the order of their relative importance 278
Efiect of thickness of shaving on cutting speed most important subject for experiment .- .291 Experiments showing effect upon cutting speed of varying the thickness of the shaving, a tool with straight edge being used, removing in all cases . a shaving exactly one inch long 292
Experiments showing effect upon cutting speed of varying the depth of the cut, a tool with straight edge being used, removing in all cases a shaving 0.03 inch thick . .299
WHY CUTTING EDGE OF TOOL SHOULD BE CURVED
Principal object in having the cutting edge of tools curved is to insure against damage to the finished surface of the work . . . . . . . . . . . . . . . . . . .
307
Tools with the broad noses having for their cutting edges curves of large radius best to use except for risk of chatter . . . . . . . . . . . . . . . . . . . . . . . . .
312
Reasons why cutting edge with comparatively small radius of curvature tends to avoid chatter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 Dr. Nicolson’s experiments showing wavelike increase and diminution in thepressure of the chip on the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
Reasons for adopting the particular curve chosen for the cutting edge of our standard tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
LIP AND CLEARANCE ANGLE OF TOOLS
For important conclusions on this subject, sec paragraphs 335, 341 to 354
Clearance angle of the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
Clearance angle of from 9° to 12° should be used in shops in which each machinist grinds his own tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
Lip angle of the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
Most important consideration in choosing lip angle is to make it sufficiently blunt to avoid danger of crumbling or spalling off at cutting edge . . . . . . . 355
Why tool for cutting soft cast iron should have blunter lip angle than tool for cutting soft steel . . . . . . . .‘ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
Theory as to why an acute lip angle produces a higher speed for cutting soft steel and a slower speed for soft cast iron . . . . . . . . . . . . . . . . . . . . . . . . 373
Why tools should be ground with greater side slope than back slope . . . . . . . . . 376
Side slope and back slope as affected by the grinding . . . . . . . . . . . . . . . . . . . . . 379
Side slope and back slope as they affect the direction of the chip . . . . . . . . . . . . .380
Tendency of the pressure of the chip to bend the tool to one side . . . . . . . . . . . . 382 '~
63 Efiect of side slope and back slope upon the power required to feed the tool . . 383
Back slope needed to secure better finish and greater accuracy in size . . . . . . . 386
FORGING AND GRINDING TOOLS
For important conclusions on this subject, see paragraphs 392 to 414
PARAGRAPH Shape of tools as afiected by grinding and forging . . . . . . . . . . . . . . . . . . . . . . . . 391 Grinding tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
Size and proportion of body of the tool . . . . . . . . . . . . . . . . . . . . . . . . . . .-. . . . . 415
Importance of bending nose of tool over to one side to avoid danger of upsetting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
Importance of lowering tool supports in designing machine tools . . . . . . . . . . . . 426
Length of shanks of cutting tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427
Tools should be designed so that largest amount of work can be done for smallest combined cost of forging and grinding . . . . . . . . . . . . . . . . . . . . . . . 431
Best method of forging a. tool is to bend or turn up its end . . . . . . . . . . . . . . . . . 442
Kicking the bar of tool steel and breaking it off cold a bad practice . . . . . . . . . . 445
Heating the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 447 Bending or tuming up the nose of the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
Drawing down the heel of the tool to secure a good bearing . . . . . . . . . . . . . . . . 454
Cutting ofi corners of nose of tool to save work in grinding . . . . . . . . . . . . . . . . . 456
Cutting to correct height and lip angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458
Bending or setting the nose of the tool over to one side and truing up the whole tool . . . . . . . . .' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459 Fire or heat cracks in tools come from four principal causes . . . . . . . . . . . . . . . . 461 Relative work to be done in the smith shop and on the grinding machine for maximum economy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470 Limit gage for dressing tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 Importance of using a heavy stream of water directly on nose of tool in grinding . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 Tools with keen lip angles (11. e., steep side slope) much more expensive to grind than blunt lip angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478 Fiat surfaces tend to heat the tools in grinding . . . . . . . . . . . . . . . . . . . . . . . . . . 481 Selection of the emery wheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483 Desirable features in an automatic tool grinding machine . . . . . . . . . . . . . . . . . 484 Desi:-ability of alarge su] ply of tools, a complete tool room, and an auto- matic grinding machine even in a small shop . . . . . . . . . . . . . . . . . . . . . . 486
PRESSURE OF THE CHIP UPON THE TOOL
Summary of conclusions of English, German and American Experimenters (See Folder 12, Table 83) F or important conclusions on this subject, see Folder 12, Table 83, and para- graphs 536 to 541, and 567 to 572, and 581
Cutting speed and pressure of chip on the tool compared for steel . . . . . . . . . . . 502
Theory as to why no accurate relations exist between pressure on tool and cutting speed, tensile strength, etc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506 1 .
PARAGRAPH Cutting speed and pressure of chip on the tool com pared for east iron . . . . . . . 520 Cutting speed and crushing strength compared for cast iron . . . . . . . . . . . . . . . 521
Cast iron and steel compared in the relation of cutting speed to pressure on tool . 522
Apparatus used and method of making experiments on the pressure of chip on the tool in cutting cast iron and steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
Apparatus used in experiments on pressure of chip on the tool . . . . . . . . . . . . . 531
Details of experiments upon the pressure of the chip on the tool in cutting cast iron with our standard tools with various feeds and depths of cut . .
535 Object of E}lp8l'lII‘l8l1tB on pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542
Effect of the size of the standard tool upon the pressure of the chip on the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
Effect of a thin chip and shallow depth of cut in increasing the pressure on the tool is the same for hard as for soft cast iron . . . . . . . . . . . . . . . . . . . . . 562
Details of experiments upon the pressure of the chip on the tool in cutting steel with our standard tools with various feeds and depths of cut . . . . . . 566
Pressure of chip on tool the same whether fast or slow cutting speeds are used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576
Power required to feed the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
Apparatus for determining the power required to feed the tool . . . . . . . . . . . . .
585
COOLING THE TOOL WITH HEAVY STREAM OF WATER
For important conclusions on this subject, see Folder 15, Table 110, and para- graphs 598 to 606, and 631
Effect upon the cutting speed of pouring a heavy stream of water upon the cutting edge of the tool_ . . . . . . . . . . . . . . . . . . . . . . . . . . . . .> . . . . . . . . . . . . . 593
Portion of the tool on which the water jet should be thrown . . . . . . . . . . . . . . . 607
Forty per cent gain in cutting speed from throwing a heavy stream of water upon the tool in cutting steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 610
Details of typical experiment for determining gain through heavy stream of water on the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617
Sixteen per cent gain in cutting speed from throwing a heavy stream of water upon the tool in cutting cast iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625
Percentage of gain the same whether thin or thick chips are being removed . . 630
CHATTER OF TOOLS
For important conclusions on this subject, see 634 to 647
Chatter caused by the nature of the work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
Chatter caused by the method of driving the work . . . . . . . . . . . . . . . . . . . . . . 636
Chatter caused by cutting tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637 Chatter connected with the design of the machine . . . . . . . . . . . . 1 . . . . . . . . . 641
Efiect of chatter upon the cutting speed of the tool _ . . . . . . . . . . . _ . . . . . . . . 646 Massive tools needed for high speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650
Steady rest economical in turning any piece of metal whose length is more than twelve times its diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 669
Efieet of chatter upon the cutting speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
Experiment showing that chatter causes a reduction in cutting speed of 10 per cent to 15 per cent whether the tools are run with or without water to cool them . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674
Higher cutting speed can be used with an intermittent cut than with a steady cut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
678
HOW LONG SHOULD A TOOL RUN BEFORE REGRINDING
For important conclusions on this subject, see paragraphs 682 to 692 . PARAGRAPH lhe effect upon cutting speed of the duration of the cut; i. e., the time which the tool must last under pressure of the chip without being reground . . . .681
Efiect upon cutting speed of duration of cut, modern high speed tools being used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
Effect upon cutting speed of duration of cut, carbon tempered tools being used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706
Effect upon cutting speed of duration of cut with modern high speed tools and carbon tempered tools compared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708
Effect upon cutting speed of duration of cut, in cutting cast iron . . . . . . . . . . . 709
The most economical duration of the cut in cutting steel . . . . . . . . . . . . . . . . . . .
718
EFFECT OF FEED AND DEPTH OF CUT ON CUTTING SPEED
For important conclusions on this subject, see paragraphs 729 to 736
Effect of varying the feed and depth of cut upon the cutting speed . . . . . . . . . . 729 Importance of the study of effect of feed and depth of cut upon cutting speed and the difliculties attending these experiments . . . . . . . . . . . . . . . . 737 Practical tables giving cutting speeds corresponding to different depths of cut and thickness of feed on hard, medium and soft steel, and on hard, medium and soft cast iron, when best modern high speed tools of our standard shapes are used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743 Experiments showing effect upon cutting speed of varying the thickness of the shaving, a tool with straight edge being used, removing a shav- ing in all cases exactly one inch long . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 761 Experiments showing the effect of cutting speed of varying the depth of the cut, a tool with straight edge being used, removing in all cases a shaving 0.03 inch thick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765 Effect of varying the thickness of feed and depth of cut upon the cutting speed when our standard round nose tools are used in cutting steel . . . . . . 767 l-‘ormulm, etc _ _ _ _ . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 773 Experiments with § inch standard round nosed tool (shown on Folder 5, Fig. 24) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 782 Experiment with standard 1 inch tool (shown on Folder 5, Fig. 25a) . . . . . . . . 787 Experiment with standard } inch tool (shown on Folder 5, Fig. 25d) . . . . . . . . 787 Effect of varying the thickness of feed and depth of cut upon cutting speed when our standard round nosed tools are used in cutting east iron . . . . . . 795 Experiments with a i inch standard round nosed tool (shown on Folder 5 Fig. 25b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 804 Influence which the quality of metal being cut has upon the effect of vary- ing the feed and depth of cut on the cutting speed . . . . . . . . . . . . . . . . . . . . _
815
Chemical composition and heat treatment of tool steels . . . . . . . . . . . . . . . . . . . 934 Brief historical reference to the development of steel for cutting tools . . . . . . . . 935 Ordinary tool steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 940 Hardening and tempering ordinary tool steel . . . . . . . . . . . . . . . . . . . . . . . . . . 941
Difficulties in hardening and tempering ordinary tool steel . . . . . . . . . . . . . . . . 943 Mushet or self-hardening steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 950 Four epochs in history of steel tools: (1) carbon tool steel era; (2) self-harden- ing steel era; (3) discovery of high speed tools; (4) modern high speed tools with analyses of tools of these eras . . . . . . . . . . . . . . . . . . . . . . . . . . . . 952 Experiments comparing Mushet and other self-hardening and carbon tools . . . 956 Nature of the invention of modem high speed tools . . . . . . . . . . . . . . . . . . . . . . 954 Quality of "Red Hardness” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 965 General comparison of the ingredients of carbon tools, self-hardening tools and modern high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 969 Addition of vanadium in small quantities improves quality of high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 972 General treatment of high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973 No improvement made in the heat treatment of high speed tools since their ~ discovery by Messrs. Taylor and White in 1898-99 . . . . . . . . . . . . . . . . . . . 973 First or high heat treatment for high speed tools; heating tools close to the melting point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 979 Cooling high speed tools from the high heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 982 Brief description of first or high heat treatment . . . . . . . . . . . . . . . . . . . . . . . . . . 989 Second or low heat treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 991 Brief description of second or low heat treatment . . . . . . . . . . . . . . . . . . . . . . . . 994 Uniformity the most important quality in cutting tools . . . . . . . . . . . . . . . . . . . 996 Little attention need be paid to the special directions given by makers of high speed tool steels for their treatment. All good high speed steels should be treated in the same simple way . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1001 Best method of treating tools in small shops . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1007 Coke fire preferable to soft coal for heating tools close to melting point in average smith shop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1010 Importance of not overheating high speed tools in grinding _ , . . . . . . . . . . . . .1016 Chemical composition of tool steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1020 Important characteristics of high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1021 Folder 20, Table 38, giving the analyses and cutting speeds of many of the latest high speed tools, and acomparison of these tools with Mushet self- hardening tools, and the original high speed tools as developed by Messrs. Taylor and White . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1020-1094 Chemical analysis and cutting speeds of the best modern high speed tools . . . . 1030 Recent comparison of cutting speed of best modern high speed tools with. that of former typical tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1033 Best chemical composition for modern high speed tools . . . . . . . . . . . . . . . . . . .1034 Carbon tool steels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1035 Table giving the analyses of self-hardening tools and ordinary carbon tools as used before the discovery of high speed tools . . . . . . . . . . . . . . . . . . . . . . 1035 Tools which are not self-hardening and yet contain tungsten or chromium . . .
1036
Psnaoaarri Table giving analyses and cutting speeds of various tools experimented with by Messrs. Taylor and White in the discovery and development of the high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1042 Discussion of the effect of each of the following elements upon high speed tools as originally developed ; tungsten , chromium, carbon , molybdenum , manganese, silicon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1045 Molybdenum as a substitute for tungsten in high speed .tools . . . . . . . . . . . . . . . 1053 Best modern high speed tool compared with original high speed tools developed by Messrs. Taylor and White . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1058 Features of improvement in high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1064 Principal chemical changes made in best modern high speed tool over origi- nal high speed tool developed by Messrs. Taylor and White . . . . . . . . . . .1079
Discovery by Messrs. Taylor and White that small quantities ofpvanadium improve high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1088 THEORY OF HARDENING STEEL For data concerning Theory of Hardening Steel, see paragraphs 1095 to 1128
QUALITY OF METAL BEING CUT
Efiect of the quality of the metal being cut upon cutting speed . . . . . . . . . . . . .1129
Systematic classification of steel forgings and castings according to their cutting speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1141
Efiect of the quality or hardness of steel forgings upon the cutting speed . . . . . 1133
Best guide to hardness as it affects cutting speed lies in the physical proper- ties of steel as indicated by the tensile strength and percentage of stretch and the contraction of area of standard tensile test bars cut from the body of the forging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 . .1143 Effect of the quality or hardness of cast iron upon the cutting speed . . . . . . . . 1157 Quality of red hardness in tools plays a much smaller part in cutting cast iron than in cutting steel. Therefore with high speed tools there is a much less percentage of gain in cutting cast iron than in cutting steel . . . . . . . . 1159
Cutting speed of castings as found in the average machine shop . . . . . . . . . . . . 1165
LINE OR CURVE OF CUTTING EDGE
Effect of line or curve of the cutting edge on the cutting speed . . . . . . . . . . . . . . 1169 Tr,-ol with cutting edge having a curved outline produces a chip varying in thickness at all points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1171 Large curve for cutting edge. Thinning down the shaving produces faster cutting speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1172 Cutting speeds of our standard tools of different sizes compared when using the same depth of cut and feed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
iii-Xperiments upon the cutting speeds of parting tools and thread tools . . . . .1175 Practical rule for finding proper cutting speed for a parting tool when high speed steel of quality of tool No. 1, Folder 20, is used . . . . . . . . . . . . . . . . .1181 Practical rule for finding proper cutting speed for a thread tool when high speed steel of the quality of tool No. 1, Folder 20, is used . . . . . . . . . . . . . . 1184 Cutting speed of broad nosed tools with straight line cutting edge compared with standard Q inch round nosed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1186
For data regarding Slide Rules, see paragraphs 1188 lo 1197
ADDITIONAL EXPERIMENTS AND INVESTIGATIONS For data conceming additional experiments and investigations, sec pamgmph 1108
Paragraphs
Object of Part 2 of the Paper
130 There are three principal objects in writing this section of the paper.
131 (A) To record and make public the results of our experiments to date as embodied in laws, etc., and the incorporation of these laws in slide rules for practical, everyday use.
132 (B) To describe the methods, principles and apparatus which should be used in making investigations of this type, and warn future experimenters against the errors into which we, as well as most other investigators in this field, have fallen.
I33 (C) To indicate the additional experiments which are needed to perfect our knowledge of the art, in the hope of inducing others to join us in carrying on and completing this work, both in the interest of science and of the many users of machine tools the world over; and to warn others against a certain class of experiments which are alluring. appear to ofler great opportunities, but which, in fact, are fruit- less.
134 The writer wishes to emphasize the fact that, while many of our experiments have a certain scientific value, and while it has been our effort to conduct all of our work upon scientific principles, yet the main object of this investigation has been the thoroughly practical one of enabling us to get more, better and cheaper work out of a machine shop.
135 The problem before us may be again briefly stated to consist cf a careful study of the effect which each of the twelve following variable elements has upon the selection of the CUTTING SPEED or THE root: “The subjects treated in this section of the paper are from their nature so dependent one upon another, and so interwoven, that the writer has had difficulty in treating them consecutively and logically. He therefore trusts that a certain amount of repetition and the necessity for referring frequently from one part of the paper to another will be pardoned.
a The quality of the metal which is to be cut, i. e., its hardness or other qualities which affect the cutting speed;
b The diameter of the work;
c The depth of the cut, or one-half of the amount by which the forging or casting is being reduced in diameter in turning;
d The thickness of the shaving, or the thickness of the spiral strip or band of metal which is to be removed by the tool, measured while the metal retains its original density ; not the thickness of the actual shaving, the - metal of which has become partly disintegrated;
e The elasticity of the work and of the tool;
f The shape or contour of the cutting edge of the tool, together with its clearance and lip angles;
g The chemical composition of the steel from which the tool is made, and the heat treatment of the tool ;
h Whether a heavy stream of water, or other cooling medium, is used on the tool;
j The duration of the cut, i. e., the time which a tool must last under pressure of the shaving without being reground; '
k The pressure of the chip or shaving upon the tool;
l The changes of speed and feed possible in the lathe;
m The pulling and feeding power of the lathe at its various speeds.
136 It is of course superfluous to call the attention of those who have given much thought to the subject of cutting metals as an art, to the fact that the ultimate object of all experiments in this field is to learn how to remove the metal from our forgings and castings in the quickest time, and that therefore the art of cutting metals may be briefly defined as the knowledge of how, with the limitations caused by some and the opportunities offered by others of the above twelve variable elements, in each case to remove the metal with the highest appropriate cutting speed. And yet a walk through almost any machine shop will convince anyone that if those in charge of the shop are aware of the effect of speed upon economy, they are acting upon this information only in a few sporadic cases and by no means systematically.
137 Before entering upon the details of our experiments, it seems necessary to again particularly call attention to the fact that “standard cutting-speed” is the true criterion by which to measure the effect of each of these twelve variables upon the problem. The writer therefore repeats what he has before said in paragraph 64 (Part 1): “THE EFFECT or sacs vxnraann oron THE 1>noa1.r-11.1 rs assr DETERMINED at rrsnrrqo THE nxxca" nun or corrrno srann (ear, IN FEET ran MINUTE) WHICH wnx. cause THE TOOL TO an COMPLETLY numnn arrsn nxvmo sass aux son 20 armuwss UNDER rmrsorm CONDITIONS."
138 To give another illustration of our practical use of this standard. If, for example, we wish to determine which make of tool steel is the best, we should proceed to make from each of the two kinds to be tested a set of from four to eight tools. Each tool should be forged from tool steel, say, 5- inch x 1§ inch and about 18 inches long, to exactly the same shape, and after giving the tools made from each type of steel the heat treatment appropriate to its chemical com- position, they should all be ground with exactly the same shaped cutting edge and the same clearance and lip angles. One of the sets of eight tools should then be run, one tool after another, each for a period of 20 minutes, and each at a little faster cutting speed than its predecessor, until that cutting speed has been found which will cause the tool to be completely ruined‘ at the end of 20 minutes, with an allowance of a minute or two each side of the 20-minute mark.
139 Every precaution must be taken throughout these tests to maintain uniform all of the other elements or variables which affect the cutting speed, such as the depth of the cut and the quality of the metal being cut. The rate of the cutting speed must be frequently tested during each 20-minute run to be sure that it is uniform throughout. For further details in making tests, see paragraphs 175 to 262.‘
140 Throughout this paper, “the speed at which tools” give out in 20 minutes, as described above, will be, for the sake of brevity, referred to as the “standard speed.” ~
141 After having found the “standard speed” of the first type of tools, and having verified it by ruining several more of the eight tools at the same speed, we should next determine in a similar manner the exact speed at which the other make of tools will be ruined in 20 minutes; and if, for instance, one of these sets of tools exactly ruins at a cutting speed of 55 feet, while the other make ruins at 50 feet per minute, these “standard speeds," 55 to 50, constitute by far the most important criterion from which to judge the relative economic value of the two steels for a machine shop. ‘For the advantage of completely ruining a tool in experimenting as 8- standard method see paragraph 151.
142 Other properties of the steels, as mentioned in paragraphs 934 to 1094, must of course be considered in choosing a tool steel. But if the steels are in other respects equal, their maximum cutting speeds then represent the exact measure of their values.
143 Perhaps the best criterion by which to judge of the value of any standard or test is the ability to duplicate the results which have been once obtained. We have repeatedly been able to reduplicate the results obtained through this standard within an error of 2 per cent. For our reasons for adopting the 20 minute period as our standard running time see paragraphs 175 to 184. “STANDARD SPEED" BEST TEST FOR DETERMINING VALUE or TOOLS, ETC.
144 It seems necessary early in this paper to emphasize the importance of the “standard speed” as being the true test for the relative value of tools as well as for the other elements involved in the art of cutting metals——the more so since the accuracy and delicacy of this standard are but vaguely recognized.
145 Among those commonly referred to, the most deceptive and unreliable standard as to the relative value of tools is THE LENGTH or TIME A TOOL WILL RUN BEFORE REQUIRING GRINDING or before being ruined. So many people are continually being misled by this standard that its inadequacy can scarcely be over-emphasized.
146 To illustrate: Let us assume, for instance, that three tools have been proved to be uniform within, say, 2 per cent by our standard method, described in paragraph 138, and to have a “standard speed” of 60 feet per minute for a run of 20 minutes. If then the cutting speed of each of these tools is increased, say, to 63 feet per minute, THE LENGTH OF TIME wmcn THEY WILL RUN at this slight increase in cutting speed will be almost sure to vary greatly. One of the tools will be ruined, say, in six minutes, another in nine minutes, while the third may last 15 minutes. Thus if tools which are uniform within 2 per cent are run only slightly beyond “standard speed,” they are likely to vary to the extent of more than 2 to 1 in time which they last before ruining or requiring regrinding; and so the misleading nature of the standard becomes apparent.
147 The great variation in the time which carefully standardized tools will last when run at an increase in cutting speed of only one foot per minute will be seen by examining table {in paragraph 619. In this case it will be seen that an increase of only one foot in cutting speed causes standardized tools to vary in their running period, in the two extreme cases, between the periods of 1.5 minutes and 17.5 minutes. A study of this table will show that the value of the tools is closely given by standard cutting speeds, but that it is in no sense proportional to the time which the tool runs before being ruined. This matter will be further discussed in paragraph 619. etc.
148 The inadequacy of this standard is, however, so little recognized that even as able an experimenter as Dr. Nicolson, after having written the record of the “Manchester Experiments,” and then made his own admirable “ Dynamometer Experiments, ” falls into the error of adopting this false standard in his “Experiments on Durability of Difierent Cutting Angles,” described in his paper in Tabla 5, 6 and 7, and in paragraphs 38 to 44 inclusive, pp. 657 to 661. Yet in these very experiments the misleading nature of this standard will be seen. Note that in Table 7, for instance, a 75 degree angle tool at a cutting speed of 74 feet per minute lasts only 2 minutes 10 seconds, while the same tool when run only one foot per minute slower at a cutting speed of 73 feet per minute lasts 10 minutes and 37 seconds.
149 For many years it has been usual for salesmen of tool steels to give detailed accounts of the number of hours which tools made from their steels, would cut metals without the necessity of regrinding. In fact, tool steel literature abounds in statements of the long life of tools with one grinding, implying that this is the proper standard for measuring their value. By referring, however, to paragraphs 693 and 710 it will be seen that for ninety-nine one-hundredths of the work of a shop, this criterion is of no value whatever, and that the man who boasts of having run a tool without regrinding, say, for a longer period than one and one-half hours on ordinary shop work, is merely boasting of how little he knows about the art of cutting metals cheaply.
150 The writer has already referred in paragraph 92 (Part 1) to another error into which all experimenters in this art fall sooner or later: namely, that of concluding that the effect which the size, shape and angles of the tool has upon the problem of cutting metals can best be determined by a careful investigation of the effect which each of these elements has upon the pressure required to remove a given sized chip or shaving. The reasoning used is that that tool is the best which is so shaped as to remove a given chip or shaving with the least amount of pressure or cutting force. The utter fallacy of this as a measure of the value of the tool has already been referred to in paragraph 92, and will be again referred to in paragraph 135.
151 In paragraph 59 (Part 1) the writer has described several false standards which were adopted by us, one after another, for determining when a tool had been run at its maximum cutting speed. Even with these defective standards we obtained most useful results. Broadly speaking, however, our reason for successively abandoning each of these standards was the impossibility of accurately reduplicating the results obtained. And this after all remains the best gage of the value of experimental methods. In all cases the earlier standards adopted by us required very close observation and judgment on the part of the experimenter to determine when the tool had reached that state of deterioration which was appropriate to its highest cutting speed. The advantage of our present standard, namely, that of completely ruining the tool, lies in-the fact that it is an unmistakable, clear-cut phenomenon which calls for a minimum of judgment on the part of the operator, and thus eliminates one of the sources of human error in the experiments, and enables us to reduplicate our results with accuracy.
152 On Folder 3, Fig. 17b, are shown two views of a tool which has been completely ruined according to this standard.
ACTION OF TOOL AND ITS WEAR IN CUTTING METALS THE ACTION OF THE NOSE OF THE TOOL
161 In shearing steel, the metal at the point of rupture is pulled apart under a tensile strain, although on each side of the shearing line the metal is under heavy compression.
163 There is no question that shearing takes place constantly along the left hand edges of two of the sections of the chip at the same time, and it is probable that this action occurs most of the time along three lines of cleavage. See paragraph 167.
164. Dr. Nicolson’s dynamometer experiments show that the pressure of the chip on the tool in cutting a chip of uniform section varies with wavelike regularity, and that the smallest pressure of the chip is not less than two-thirds of the greatest pressure. From this it is evident that shearing must be taking place along at least two lines of cleavage at the same time; since if each of the sections into which the chip is divided were completely broken off before the tool began to break off the following section, it is evident that there would be times when there was almost no pressure from the chip on the tool.
166 It is probable that after the shearing action has progressed in section 3 to about the point indicated by Ta, that the whole of this section gives way or shears with a rather sudden yielding of the metal from T, , to the upper surface of the chip. It is this rather sudden shearing point which undoubtedly causes the wavelike diminution in the pressure of the chip indicated in Dr. Nicolson’s experiments, referred to in paragraph 316.
169 Throughout this paper the important facts stated by us have been verified by many and carefully made experiments; and we therefore trust that our readers, if unable to accept our theories, will at least have respect for our facts.
ACTION OF CUTTING EDGE OF TOOL IS THAT OF SCRAPING - CUTTING EDGE NOT UNDER HEAVY PRESSURE
170 It would appear that the chip is torn off from the forging at a point appreciably above the cutting edge of the tool and this tearing action leaves the forging in all cases more or less jagged or irregular at the exact spot where the chip is pulled away from the forging, as shown to the left of T1. An instant later the line of the cutting edge, or more correctly speaking, the portion of the lip surface immediately adjoining the cutting edge, comes in contact with these slight irregularities left on the forging owing to the tearing action, and shears these lumps off, so as to leave the receding flank of the forging comparatively smooth.
171 Thus in this tearing action, particularly in the case of cutting a thick shaving, while the cutting edge of the tool is continually in action, scraping or shearing off or rubbing away these small irregularities left on the forging, yet that portion of the lip surface close to the cutting edge constantly receives much less pressure from the chip than the same surface receives at a slight distance away from the cutting edge. This allows the tool to run at higher cutting speeds than would be possible if the cutting edge received the same pressure as does the lip surface close to it.
172 There are many phenomena which indicate this tearing action of the tool. For example, it is an everyday occurrence to see cutting tools which have been running close to their maximum speeds and which have been under cut for a considerable length of time, guttered out at a little distance back of the cutting edge, as shown in Folder 3, Fig. 17e. The wear in this spot indicates that the pressure of the chip has been most severe at a little distance back from the edge.
173 Still another manner in which in many cases the tearing action of the tool is indicated is illustrated in Folder 3, Fig. 17a, in which a small mass of metal D is shown to be stuck fast to the lip surface of the tool after it has completed its work and been removed from the lathe. When broken off, however, and carefully examined, this mass will be found to consist of a great number of small particles which have been cut or scraped off of the forging, as above described, by the cutting edge of the tool. They are then pressed down into a dense little pile of compacted particles of steel or dust stuck together and to the lip surface of the tool almost as if they had been welded. In the case of the modern high speed tools, when this little mass of dust or particles is removed from the upper surface of the tool, the cutting edge will in most cases be found to be about as sharp as ever, and the lip surface adjacent to it when closely examined will show in many cases the scratches left by the emery wheel from the original grinding of the tool.
174 With roughing tools made from old fashioned tempered steel, however, and which have been speeded close to their “standard speeds," in most cases after removing this “dust pile” from the lip surface, the cutting edge of the tool will be found to be distinctly rounded over. And in cases where the tool has been cutting a very thick shaving, the edge will be very greatly rounded over, as shown in the enlarged view of the nose of a tool in Folder 7, Fig. 41.
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‘For further evidence that the chip is torn away from the body of the forging somewhat as shown at T,, see paragraphs 170-174.
Updated on 28 May 2020, 30 June 2019
Object of Part 2 of the Paper . . 130
Problem consists in study of efiect of twelve variables on cutting speed of tool 135
Cutting speed (20-minute cut) standard by which to measure effect of each variable, with illustration of practical application of standard 137
“Standard speed." Best method for determining value of tools, etc., 138 to 144
False standards in common use. Time tool will last 145
ACTION OF TOOL AND ITS WEAR IN CUTTING METALS
Action of the nose of the tool . . . . 153
Metal torn away, not cut or wedged 153
Analysis of strains in chip and forging 156
Action of cutting edge is that of scraping cutting edge not under heavy pressure 170
Nature of wear on tools depends on whether it has been chiefly caused by heat 175
Three classes of wear (1) heat, (2) heat and friction combined, (3) friction without heat 177
Reason for adopting standard test period of 20 minutes 183
“ Economical” cutting speeds 185
How carbon steel tempered and tools made from old fashioned self-hardening steel wear 189
How modern high-speed tools wear 201
HOW TO MAKE AND RECORD EXPERIMENTS
Art of experimenting defined as determining effict of varying one element while all others are held constant 210
Met al which is to be cut . 213
Experimental lathe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
217
Speed changes on the machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
222
Feeding mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
224
Weight of the machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
226
Best type of experimental lathe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
227
Measuring the cutting speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
230
Measuring the depth of cut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
238
If niformity in the cutting tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
245
Where practicable in experimenting no cuts lighter than 1%; inch depth by 3*; inch feed should be taken . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
252
More time required in preparation than in experimenting . . . . . . . . . . . . . .
254
Recording the details and results of experiments . . . . . . . . . . . . . . . . . . . . . . . . .
257
—i_,_ _ Operator’s daily record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
258
Summary sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
259
Each law and diagram the result of several series of experiments . . . . . . . . . . .
263
PROPER SHAPE FOR STANDARD SHOP ROUGHING TOOLS
A few carefully considered types of tools better than great variety . 268
Standard tools illustrated . . 269
Conflict between the difiercnt objects to be attained in cutting metals which affect the design of standard tools . 271
Elements affecting cutting speed of tools in the order of their relative importance 278
Efiect of thickness of shaving on cutting speed most important subject for experiment .- .291 Experiments showing effect upon cutting speed of varying the thickness of the shaving, a tool with straight edge being used, removing in all cases . a shaving exactly one inch long 292
Experiments showing effect upon cutting speed of varying the depth of the cut, a tool with straight edge being used, removing in all cases a shaving 0.03 inch thick . .299
WHY CUTTING EDGE OF TOOL SHOULD BE CURVED
Principal object in having the cutting edge of tools curved is to insure against damage to the finished surface of the work . . . . . . . . . . . . . . . . . . .
307
Tools with the broad noses having for their cutting edges curves of large radius best to use except for risk of chatter . . . . . . . . . . . . . . . . . . . . . . . . .
312
Reasons why cutting edge with comparatively small radius of curvature tends to avoid chatter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 Dr. Nicolson’s experiments showing wavelike increase and diminution in thepressure of the chip on the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
Reasons for adopting the particular curve chosen for the cutting edge of our standard tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
LIP AND CLEARANCE ANGLE OF TOOLS
For important conclusions on this subject, sec paragraphs 335, 341 to 354
Clearance angle of the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
Clearance angle of from 9° to 12° should be used in shops in which each machinist grinds his own tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
Lip angle of the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
Most important consideration in choosing lip angle is to make it sufficiently blunt to avoid danger of crumbling or spalling off at cutting edge . . . . . . . 355
Why tool for cutting soft cast iron should have blunter lip angle than tool for cutting soft steel . . . . . . . .‘ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
Theory as to why an acute lip angle produces a higher speed for cutting soft steel and a slower speed for soft cast iron . . . . . . . . . . . . . . . . . . . . . . . . 373
Why tools should be ground with greater side slope than back slope . . . . . . . . . 376
Side slope and back slope as affected by the grinding . . . . . . . . . . . . . . . . . . . . . 379
Side slope and back slope as they affect the direction of the chip . . . . . . . . . . . . .380
Tendency of the pressure of the chip to bend the tool to one side . . . . . . . . . . . . 382 '~
63 Efiect of side slope and back slope upon the power required to feed the tool . . 383
Back slope needed to secure better finish and greater accuracy in size . . . . . . . 386
FORGING AND GRINDING TOOLS
For important conclusions on this subject, see paragraphs 392 to 414
PARAGRAPH Shape of tools as afiected by grinding and forging . . . . . . . . . . . . . . . . . . . . . . . . 391 Grinding tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
Size and proportion of body of the tool . . . . . . . . . . . . . . . . . . . . . . . . . . .-. . . . . 415
Importance of bending nose of tool over to one side to avoid danger of upsetting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
Importance of lowering tool supports in designing machine tools . . . . . . . . . . . . 426
Length of shanks of cutting tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427
Tools should be designed so that largest amount of work can be done for smallest combined cost of forging and grinding . . . . . . . . . . . . . . . . . . . . . . . 431
Best method of forging a. tool is to bend or turn up its end . . . . . . . . . . . . . . . . . 442
Kicking the bar of tool steel and breaking it off cold a bad practice . . . . . . . . . . 445
Heating the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 447 Bending or tuming up the nose of the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
Drawing down the heel of the tool to secure a good bearing . . . . . . . . . . . . . . . . 454
Cutting ofi corners of nose of tool to save work in grinding . . . . . . . . . . . . . . . . . 456
Cutting to correct height and lip angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458
Bending or setting the nose of the tool over to one side and truing up the whole tool . . . . . . . . .' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459 Fire or heat cracks in tools come from four principal causes . . . . . . . . . . . . . . . . 461 Relative work to be done in the smith shop and on the grinding machine for maximum economy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470 Limit gage for dressing tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 Importance of using a heavy stream of water directly on nose of tool in grinding . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473 Tools with keen lip angles (11. e., steep side slope) much more expensive to grind than blunt lip angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478 Fiat surfaces tend to heat the tools in grinding . . . . . . . . . . . . . . . . . . . . . . . . . . 481 Selection of the emery wheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483 Desirable features in an automatic tool grinding machine . . . . . . . . . . . . . . . . . 484 Desi:-ability of alarge su] ply of tools, a complete tool room, and an auto- matic grinding machine even in a small shop . . . . . . . . . . . . . . . . . . . . . . 486
PRESSURE OF THE CHIP UPON THE TOOL
Summary of conclusions of English, German and American Experimenters (See Folder 12, Table 83) F or important conclusions on this subject, see Folder 12, Table 83, and para- graphs 536 to 541, and 567 to 572, and 581
Cutting speed and pressure of chip on the tool compared for steel . . . . . . . . . . . 502
Theory as to why no accurate relations exist between pressure on tool and cutting speed, tensile strength, etc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506 1 .
PARAGRAPH Cutting speed and pressure of chip on the tool com pared for east iron . . . . . . . 520 Cutting speed and crushing strength compared for cast iron . . . . . . . . . . . . . . . 521
Cast iron and steel compared in the relation of cutting speed to pressure on tool . 522
Apparatus used and method of making experiments on the pressure of chip on the tool in cutting cast iron and steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
Apparatus used in experiments on pressure of chip on the tool . . . . . . . . . . . . . 531
Details of experiments upon the pressure of the chip on the tool in cutting cast iron with our standard tools with various feeds and depths of cut . .
535 Object of E}lp8l'lII‘l8l1tB on pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542
Effect of the size of the standard tool upon the pressure of the chip on the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
Effect of a thin chip and shallow depth of cut in increasing the pressure on the tool is the same for hard as for soft cast iron . . . . . . . . . . . . . . . . . . . . . 562
Details of experiments upon the pressure of the chip on the tool in cutting steel with our standard tools with various feeds and depths of cut . . . . . . 566
Pressure of chip on tool the same whether fast or slow cutting speeds are used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576
Power required to feed the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
Apparatus for determining the power required to feed the tool . . . . . . . . . . . . .
585
COOLING THE TOOL WITH HEAVY STREAM OF WATER
For important conclusions on this subject, see Folder 15, Table 110, and para- graphs 598 to 606, and 631
Effect upon the cutting speed of pouring a heavy stream of water upon the cutting edge of the tool_ . . . . . . . . . . . . . . . . . . . . . . . . . . . . .> . . . . . . . . . . . . . 593
Portion of the tool on which the water jet should be thrown . . . . . . . . . . . . . . . 607
Forty per cent gain in cutting speed from throwing a heavy stream of water upon the tool in cutting steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 610
Details of typical experiment for determining gain through heavy stream of water on the tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617
Sixteen per cent gain in cutting speed from throwing a heavy stream of water upon the tool in cutting cast iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625
Percentage of gain the same whether thin or thick chips are being removed . . 630
CHATTER OF TOOLS
For important conclusions on this subject, see 634 to 647
Chatter caused by the nature of the work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
Chatter caused by the method of driving the work . . . . . . . . . . . . . . . . . . . . . . 636
Chatter caused by cutting tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637 Chatter connected with the design of the machine . . . . . . . . . . . . 1 . . . . . . . . . 641
Efiect of chatter upon the cutting speed of the tool _ . . . . . . . . . . . _ . . . . . . . . 646 Massive tools needed for high speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650
Steady rest economical in turning any piece of metal whose length is more than twelve times its diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 669
Efieet of chatter upon the cutting speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
Experiment showing that chatter causes a reduction in cutting speed of 10 per cent to 15 per cent whether the tools are run with or without water to cool them . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674
Higher cutting speed can be used with an intermittent cut than with a steady cut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
678
HOW LONG SHOULD A TOOL RUN BEFORE REGRINDING
For important conclusions on this subject, see paragraphs 682 to 692 . PARAGRAPH lhe effect upon cutting speed of the duration of the cut; i. e., the time which the tool must last under pressure of the chip without being reground . . . .681
Efiect upon cutting speed of duration of cut, modern high speed tools being used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
Effect upon cutting speed of duration of cut, carbon tempered tools being used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706
Effect upon cutting speed of duration of cut with modern high speed tools and carbon tempered tools compared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708
Effect upon cutting speed of duration of cut, in cutting cast iron . . . . . . . . . . . 709
The most economical duration of the cut in cutting steel . . . . . . . . . . . . . . . . . . .
718
EFFECT OF FEED AND DEPTH OF CUT ON CUTTING SPEED
For important conclusions on this subject, see paragraphs 729 to 736
Effect of varying the feed and depth of cut upon the cutting speed . . . . . . . . . . 729 Importance of the study of effect of feed and depth of cut upon cutting speed and the difliculties attending these experiments . . . . . . . . . . . . . . . . 737 Practical tables giving cutting speeds corresponding to different depths of cut and thickness of feed on hard, medium and soft steel, and on hard, medium and soft cast iron, when best modern high speed tools of our standard shapes are used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743 Experiments showing effect upon cutting speed of varying the thickness of the shaving, a tool with straight edge being used, removing a shav- ing in all cases exactly one inch long . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 761 Experiments showing the effect of cutting speed of varying the depth of the cut, a tool with straight edge being used, removing in all cases a shaving 0.03 inch thick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765 Effect of varying the thickness of feed and depth of cut upon the cutting speed when our standard round nose tools are used in cutting steel . . . . . . 767 l-‘ormulm, etc _ _ _ _ . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 773 Experiments with § inch standard round nosed tool (shown on Folder 5, Fig. 24) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 782 Experiment with standard 1 inch tool (shown on Folder 5, Fig. 25a) . . . . . . . . 787 Experiment with standard } inch tool (shown on Folder 5, Fig. 25d) . . . . . . . . 787 Effect of varying the thickness of feed and depth of cut upon cutting speed when our standard round nosed tools are used in cutting east iron . . . . . . 795 Experiments with a i inch standard round nosed tool (shown on Folder 5 Fig. 25b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 804 Influence which the quality of metal being cut has upon the effect of vary- ing the feed and depth of cut on the cutting speed . . . . . . . . . . . . . . . . . . . . _
815
Chemical composition and heat treatment of tool steels . . . . . . . . . . . . . . . . . . . 934 Brief historical reference to the development of steel for cutting tools . . . . . . . . 935 Ordinary tool steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 940 Hardening and tempering ordinary tool steel . . . . . . . . . . . . . . . . . . . . . . . . . . 941
Difficulties in hardening and tempering ordinary tool steel . . . . . . . . . . . . . . . . 943 Mushet or self-hardening steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 950 Four epochs in history of steel tools: (1) carbon tool steel era; (2) self-harden- ing steel era; (3) discovery of high speed tools; (4) modern high speed tools with analyses of tools of these eras . . . . . . . . . . . . . . . . . . . . . . . . . . . . 952 Experiments comparing Mushet and other self-hardening and carbon tools . . . 956 Nature of the invention of modem high speed tools . . . . . . . . . . . . . . . . . . . . . . 954 Quality of "Red Hardness” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 965 General comparison of the ingredients of carbon tools, self-hardening tools and modern high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 969 Addition of vanadium in small quantities improves quality of high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 972 General treatment of high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973 No improvement made in the heat treatment of high speed tools since their ~ discovery by Messrs. Taylor and White in 1898-99 . . . . . . . . . . . . . . . . . . . 973 First or high heat treatment for high speed tools; heating tools close to the melting point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 979 Cooling high speed tools from the high heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 982 Brief description of first or high heat treatment . . . . . . . . . . . . . . . . . . . . . . . . . . 989 Second or low heat treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 991 Brief description of second or low heat treatment . . . . . . . . . . . . . . . . . . . . . . . . 994 Uniformity the most important quality in cutting tools . . . . . . . . . . . . . . . . . . . 996 Little attention need be paid to the special directions given by makers of high speed tool steels for their treatment. All good high speed steels should be treated in the same simple way . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1001 Best method of treating tools in small shops . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1007 Coke fire preferable to soft coal for heating tools close to melting point in average smith shop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1010 Importance of not overheating high speed tools in grinding _ , . . . . . . . . . . . . .1016 Chemical composition of tool steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1020 Important characteristics of high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1021 Folder 20, Table 38, giving the analyses and cutting speeds of many of the latest high speed tools, and acomparison of these tools with Mushet self- hardening tools, and the original high speed tools as developed by Messrs. Taylor and White . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1020-1094 Chemical analysis and cutting speeds of the best modern high speed tools . . . . 1030 Recent comparison of cutting speed of best modern high speed tools with. that of former typical tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1033 Best chemical composition for modern high speed tools . . . . . . . . . . . . . . . . . . .1034 Carbon tool steels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1035 Table giving the analyses of self-hardening tools and ordinary carbon tools as used before the discovery of high speed tools . . . . . . . . . . . . . . . . . . . . . . 1035 Tools which are not self-hardening and yet contain tungsten or chromium . . .
1036
Psnaoaarri Table giving analyses and cutting speeds of various tools experimented with by Messrs. Taylor and White in the discovery and development of the high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1042 Discussion of the effect of each of the following elements upon high speed tools as originally developed ; tungsten , chromium, carbon , molybdenum , manganese, silicon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1045 Molybdenum as a substitute for tungsten in high speed .tools . . . . . . . . . . . . . . . 1053 Best modern high speed tool compared with original high speed tools developed by Messrs. Taylor and White . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1058 Features of improvement in high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1064 Principal chemical changes made in best modern high speed tool over origi- nal high speed tool developed by Messrs. Taylor and White . . . . . . . . . . .1079
Discovery by Messrs. Taylor and White that small quantities ofpvanadium improve high speed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1088 THEORY OF HARDENING STEEL For data concerning Theory of Hardening Steel, see paragraphs 1095 to 1128
QUALITY OF METAL BEING CUT
Efiect of the quality of the metal being cut upon cutting speed . . . . . . . . . . . . .1129
Systematic classification of steel forgings and castings according to their cutting speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1141
Efiect of the quality or hardness of steel forgings upon the cutting speed . . . . . 1133
Best guide to hardness as it affects cutting speed lies in the physical proper- ties of steel as indicated by the tensile strength and percentage of stretch and the contraction of area of standard tensile test bars cut from the body of the forging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 . .1143 Effect of the quality or hardness of cast iron upon the cutting speed . . . . . . . . 1157 Quality of red hardness in tools plays a much smaller part in cutting cast iron than in cutting steel. Therefore with high speed tools there is a much less percentage of gain in cutting cast iron than in cutting steel . . . . . . . . 1159
Cutting speed of castings as found in the average machine shop . . . . . . . . . . . . 1165
LINE OR CURVE OF CUTTING EDGE
Effect of line or curve of the cutting edge on the cutting speed . . . . . . . . . . . . . . 1169 Tr,-ol with cutting edge having a curved outline produces a chip varying in thickness at all points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1171 Large curve for cutting edge. Thinning down the shaving produces faster cutting speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1172 Cutting speeds of our standard tools of different sizes compared when using the same depth of cut and feed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
iii-Xperiments upon the cutting speeds of parting tools and thread tools . . . . .1175 Practical rule for finding proper cutting speed for a parting tool when high speed steel of quality of tool No. 1, Folder 20, is used . . . . . . . . . . . . . . . . .1181 Practical rule for finding proper cutting speed for a thread tool when high speed steel of the quality of tool No. 1, Folder 20, is used . . . . . . . . . . . . . . 1184 Cutting speed of broad nosed tools with straight line cutting edge compared with standard Q inch round nosed tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1186
For data regarding Slide Rules, see paragraphs 1188 lo 1197
ADDITIONAL EXPERIMENTS AND INVESTIGATIONS For data conceming additional experiments and investigations, sec pamgmph 1108
Paragraphs
Object of Part 2 of the Paper
130 There are three principal objects in writing this section of the paper.
131 (A) To record and make public the results of our experiments to date as embodied in laws, etc., and the incorporation of these laws in slide rules for practical, everyday use.
132 (B) To describe the methods, principles and apparatus which should be used in making investigations of this type, and warn future experimenters against the errors into which we, as well as most other investigators in this field, have fallen.
I33 (C) To indicate the additional experiments which are needed to perfect our knowledge of the art, in the hope of inducing others to join us in carrying on and completing this work, both in the interest of science and of the many users of machine tools the world over; and to warn others against a certain class of experiments which are alluring. appear to ofler great opportunities, but which, in fact, are fruit- less.
134 The writer wishes to emphasize the fact that, while many of our experiments have a certain scientific value, and while it has been our effort to conduct all of our work upon scientific principles, yet the main object of this investigation has been the thoroughly practical one of enabling us to get more, better and cheaper work out of a machine shop.
135 The problem before us may be again briefly stated to consist cf a careful study of the effect which each of the twelve following variable elements has upon the selection of the CUTTING SPEED or THE root: “The subjects treated in this section of the paper are from their nature so dependent one upon another, and so interwoven, that the writer has had difficulty in treating them consecutively and logically. He therefore trusts that a certain amount of repetition and the necessity for referring frequently from one part of the paper to another will be pardoned.
a The quality of the metal which is to be cut, i. e., its hardness or other qualities which affect the cutting speed;
b The diameter of the work;
c The depth of the cut, or one-half of the amount by which the forging or casting is being reduced in diameter in turning;
d The thickness of the shaving, or the thickness of the spiral strip or band of metal which is to be removed by the tool, measured while the metal retains its original density ; not the thickness of the actual shaving, the - metal of which has become partly disintegrated;
e The elasticity of the work and of the tool;
f The shape or contour of the cutting edge of the tool, together with its clearance and lip angles;
g The chemical composition of the steel from which the tool is made, and the heat treatment of the tool ;
h Whether a heavy stream of water, or other cooling medium, is used on the tool;
j The duration of the cut, i. e., the time which a tool must last under pressure of the shaving without being reground; '
k The pressure of the chip or shaving upon the tool;
l The changes of speed and feed possible in the lathe;
m The pulling and feeding power of the lathe at its various speeds.
136 It is of course superfluous to call the attention of those who have given much thought to the subject of cutting metals as an art, to the fact that the ultimate object of all experiments in this field is to learn how to remove the metal from our forgings and castings in the quickest time, and that therefore the art of cutting metals may be briefly defined as the knowledge of how, with the limitations caused by some and the opportunities offered by others of the above twelve variable elements, in each case to remove the metal with the highest appropriate cutting speed. And yet a walk through almost any machine shop will convince anyone that if those in charge of the shop are aware of the effect of speed upon economy, they are acting upon this information only in a few sporadic cases and by no means systematically.
137 Before entering upon the details of our experiments, it seems necessary to again particularly call attention to the fact that “standard cutting-speed” is the true criterion by which to measure the effect of each of these twelve variables upon the problem. The writer therefore repeats what he has before said in paragraph 64 (Part 1): “THE EFFECT or sacs vxnraann oron THE 1>noa1.r-11.1 rs assr DETERMINED at rrsnrrqo THE nxxca" nun or corrrno srann (ear, IN FEET ran MINUTE) WHICH wnx. cause THE TOOL TO an COMPLETLY numnn arrsn nxvmo sass aux son 20 armuwss UNDER rmrsorm CONDITIONS."
138 To give another illustration of our practical use of this standard. If, for example, we wish to determine which make of tool steel is the best, we should proceed to make from each of the two kinds to be tested a set of from four to eight tools. Each tool should be forged from tool steel, say, 5- inch x 1§ inch and about 18 inches long, to exactly the same shape, and after giving the tools made from each type of steel the heat treatment appropriate to its chemical com- position, they should all be ground with exactly the same shaped cutting edge and the same clearance and lip angles. One of the sets of eight tools should then be run, one tool after another, each for a period of 20 minutes, and each at a little faster cutting speed than its predecessor, until that cutting speed has been found which will cause the tool to be completely ruined‘ at the end of 20 minutes, with an allowance of a minute or two each side of the 20-minute mark.
139 Every precaution must be taken throughout these tests to maintain uniform all of the other elements or variables which affect the cutting speed, such as the depth of the cut and the quality of the metal being cut. The rate of the cutting speed must be frequently tested during each 20-minute run to be sure that it is uniform throughout. For further details in making tests, see paragraphs 175 to 262.‘
140 Throughout this paper, “the speed at which tools” give out in 20 minutes, as described above, will be, for the sake of brevity, referred to as the “standard speed.” ~
141 After having found the “standard speed” of the first type of tools, and having verified it by ruining several more of the eight tools at the same speed, we should next determine in a similar manner the exact speed at which the other make of tools will be ruined in 20 minutes; and if, for instance, one of these sets of tools exactly ruins at a cutting speed of 55 feet, while the other make ruins at 50 feet per minute, these “standard speeds," 55 to 50, constitute by far the most important criterion from which to judge the relative economic value of the two steels for a machine shop. ‘For the advantage of completely ruining a tool in experimenting as 8- standard method see paragraph 151.
142 Other properties of the steels, as mentioned in paragraphs 934 to 1094, must of course be considered in choosing a tool steel. But if the steels are in other respects equal, their maximum cutting speeds then represent the exact measure of their values.
143 Perhaps the best criterion by which to judge of the value of any standard or test is the ability to duplicate the results which have been once obtained. We have repeatedly been able to reduplicate the results obtained through this standard within an error of 2 per cent. For our reasons for adopting the 20 minute period as our standard running time see paragraphs 175 to 184. “STANDARD SPEED" BEST TEST FOR DETERMINING VALUE or TOOLS, ETC.
144 It seems necessary early in this paper to emphasize the importance of the “standard speed” as being the true test for the relative value of tools as well as for the other elements involved in the art of cutting metals——the more so since the accuracy and delicacy of this standard are but vaguely recognized.
145 Among those commonly referred to, the most deceptive and unreliable standard as to the relative value of tools is THE LENGTH or TIME A TOOL WILL RUN BEFORE REQUIRING GRINDING or before being ruined. So many people are continually being misled by this standard that its inadequacy can scarcely be over-emphasized.
146 To illustrate: Let us assume, for instance, that three tools have been proved to be uniform within, say, 2 per cent by our standard method, described in paragraph 138, and to have a “standard speed” of 60 feet per minute for a run of 20 minutes. If then the cutting speed of each of these tools is increased, say, to 63 feet per minute, THE LENGTH OF TIME wmcn THEY WILL RUN at this slight increase in cutting speed will be almost sure to vary greatly. One of the tools will be ruined, say, in six minutes, another in nine minutes, while the third may last 15 minutes. Thus if tools which are uniform within 2 per cent are run only slightly beyond “standard speed,” they are likely to vary to the extent of more than 2 to 1 in time which they last before ruining or requiring regrinding; and so the misleading nature of the standard becomes apparent.
147 The great variation in the time which carefully standardized tools will last when run at an increase in cutting speed of only one foot per minute will be seen by examining table {in paragraph 619. In this case it will be seen that an increase of only one foot in cutting speed causes standardized tools to vary in their running period, in the two extreme cases, between the periods of 1.5 minutes and 17.5 minutes. A study of this table will show that the value of the tools is closely given by standard cutting speeds, but that it is in no sense proportional to the time which the tool runs before being ruined. This matter will be further discussed in paragraph 619. etc.
148 The inadequacy of this standard is, however, so little recognized that even as able an experimenter as Dr. Nicolson, after having written the record of the “Manchester Experiments,” and then made his own admirable “ Dynamometer Experiments, ” falls into the error of adopting this false standard in his “Experiments on Durability of Difierent Cutting Angles,” described in his paper in Tabla 5, 6 and 7, and in paragraphs 38 to 44 inclusive, pp. 657 to 661. Yet in these very experiments the misleading nature of this standard will be seen. Note that in Table 7, for instance, a 75 degree angle tool at a cutting speed of 74 feet per minute lasts only 2 minutes 10 seconds, while the same tool when run only one foot per minute slower at a cutting speed of 73 feet per minute lasts 10 minutes and 37 seconds.
149 For many years it has been usual for salesmen of tool steels to give detailed accounts of the number of hours which tools made from their steels, would cut metals without the necessity of regrinding. In fact, tool steel literature abounds in statements of the long life of tools with one grinding, implying that this is the proper standard for measuring their value. By referring, however, to paragraphs 693 and 710 it will be seen that for ninety-nine one-hundredths of the work of a shop, this criterion is of no value whatever, and that the man who boasts of having run a tool without regrinding, say, for a longer period than one and one-half hours on ordinary shop work, is merely boasting of how little he knows about the art of cutting metals cheaply.
150 The writer has already referred in paragraph 92 (Part 1) to another error into which all experimenters in this art fall sooner or later: namely, that of concluding that the effect which the size, shape and angles of the tool has upon the problem of cutting metals can best be determined by a careful investigation of the effect which each of these elements has upon the pressure required to remove a given sized chip or shaving. The reasoning used is that that tool is the best which is so shaped as to remove a given chip or shaving with the least amount of pressure or cutting force. The utter fallacy of this as a measure of the value of the tool has already been referred to in paragraph 92, and will be again referred to in paragraph 135.
151 In paragraph 59 (Part 1) the writer has described several false standards which were adopted by us, one after another, for determining when a tool had been run at its maximum cutting speed. Even with these defective standards we obtained most useful results. Broadly speaking, however, our reason for successively abandoning each of these standards was the impossibility of accurately reduplicating the results obtained. And this after all remains the best gage of the value of experimental methods. In all cases the earlier standards adopted by us required very close observation and judgment on the part of the experimenter to determine when the tool had reached that state of deterioration which was appropriate to its highest cutting speed. The advantage of our present standard, namely, that of completely ruining the tool, lies in-the fact that it is an unmistakable, clear-cut phenomenon which calls for a minimum of judgment on the part of the operator, and thus eliminates one of the sources of human error in the experiments, and enables us to reduplicate our results with accuracy.
152 On Folder 3, Fig. 17b, are shown two views of a tool which has been completely ruined according to this standard.
ACTION OF TOOL AND ITS WEAR IN CUTTING METALS THE ACTION OF THE NOSE OF THE TOOL
153 On Folder 8, Figs. 42, 43 and 44, is illustrated in enlarged views the action of a tool in cutting a chip or shaving from a forging at its proper normal cutting speed. It may be said in the case of all “roughing cuts ” that the chip is torn away from the forging rather than removed by the action which we term cutting. The familiar action of cutting, as exemplified by an axe or knife removing a chip from a piece of wood, for instance, consists in forcing a sharp wedge (11. e., one whose two flanks form an acute angle) into the substance to be cut. Both flanks of the wedge press constantly upon the wood, one flank bearing against the main body of the piece, while the other forces or wedges the chip or shaving away.
154 While a metal cutting tool looks like a wedge, its cutting edge being formed by the intersection of the “ lip surface” and “clearance surface” or flank of the tool, its action is far different from that of the wedge. Only one surface of a metal cutting tool, the lip surface, ever presses against the metal. The clearance surface, as its name implies, is never allowed to touch the forging. Thus “cutting” with a metal cutting tool consists in pressing, tearing or shearing the metal away with the lip surface of the “ wedge” only under pressure, while in the case of the axe and other kinds of cutting, both wedge surfaces are constantly under pressure.
155 After the cut has once been started, and the full thickness of the shaving is being removed, the action of the tool may be described as that of tearing the chip away from the body of the forging and then shearing it up into separate sections; the portion of the chip which has just been torn away, and which is still pressing upon the lip surface of the tool, acting as a lever by which the following portion of the chip is torn away from the main body of the metal.
156 It may be of interest to analyze to a certain extent the nature of the forces to which a chip and the forging from which it is being removed are subjected through the tearing action of the tool. The enlarged view of the chip, tool and forging, shown in Folder 8, Fig. 42, represents with fair accuracy the relative proportions which the shaving cut from a forging of mild steel (say, 60,000 lbs. tensile strength and 33% stretch) finally assumes with relation to the original thickness of the layer of metal which the tool is about to remove. It is, of course, impossible to accurately determine the extent to which various parts of the chip and forging close to the tool are under compression and tension, but in general the theory advanced is believed to be correct.
157 Referring to Folder 8, Fig. 42, the forging being cut and the nose of the tool which is removing the chip are shown on an enlarged scale. The thickness of the layer of metal about to be removed is indicated by L between the dotted line and the full line which represents the outside of the forging. It will be observed that the chip is in process of being torn apart and broken up into three sections: Section 1, which is adjoining the forging; section 2, which comes next to it, and in which rupture or cleavage has started and proceeded a a little way up from the bottom of the chip and on the left hand side, the shearing action having progressed as far as T,; section 3, in which shearing has progressed about two-thirds of the way to the top of the chip and is taking place at T,. Section 4 has been entirely sheared from its adjoining section, and has already left the lip surface of the tool.
158 On examination of the proportions of the chip it will be noticed that the width of the sections into which the chip breaks up is at their base about double the thickness of the original layer of metal which is to be removed, and that their upper portions are not enlarged to the same extent. These sections are about three times as high as the original thickness of the layer of the metal to be removed.
It should be clearly understood that the dimensions of the section of the chip will vary with each hardness of metal which is being cut, and also to a certain extent with the side and back slopes of the lip surface of the tool. The harder the metal of the forging, the less will each section into which the chip has been broken up be found to be enlarged. In other words, if the same shaped tool be used in each case the chip from soft metal enlarges or distorts very much more than the corresponding chip from hard steel. This will be referred to in paragraph 506, in explaining the reason why the total pressure on the tool has but little relation on the one hand to the cutting speed, and on the other hand to the hardness of the metal which is being cut.
159 The chip bears on the surface of the forging, say, from point H to point G, and throughout this distance is under constant compression from the lip surface of the tool. This compression is transmitted through each of the sections 1 and 2 of the chip, in the direction indicated by the small arrows, to the upper portions of these sections, which are still unbroken and act like a lever attached to the upper part of section 1 to tear‘ section 1 away from the body of the forging, as indicated at point T,. The tearing away of section 1 is also assisted by the pressure of the tool upon its lower surface.
160 After this tearing action has started, the further breaking of the chip into independent sections would seem to be that of simple shearing. It should be borne in mind that in shearing a thick piece of steel the whole piece is not shorn or cut apart at the same instant, but the line at which rupture or cleavage takes place progresses from one surface of the piece down through the metal until within a short distance from the other surface, when the whole remaining section rather suddenly gives way. '
161 In shearing steel, the metal at the point of rupture is pulled apart under a tensile strain, although on each side of the shearing line the metal is under heavy compression.
162 As each of the sections of the chip successively comes in contact with the lip of the tool, its lower surface is crushed, and the metal flows and spreads out laterally until it becomes about twice its original thickness. As in all shearing, when the full capacity for flowing of the metal has been reached, it tears apart under tensile strain from the body of the adjoining metal of the forging. The compression on the chip from the tool still continues, however, and the chips continue to flow and spread out sideways at a part higher up; i. e., farther away from the surface of the tool, at the portions marked F. In the same way shearing continually takes place at the left side of the portion of the chip which is flowing or spreading out sideways.
164. Dr. Nicolson’s dynamometer experiments show that the pressure of the chip on the tool in cutting a chip of uniform section varies with wavelike regularity, and that the smallest pressure of the chip is not less than two-thirds of the greatest pressure. From this it is evident that shearing must be taking place along at least two lines of cleavage at the same time; since if each of the sections into which the chip is divided were completely broken off before the tool began to break off the following section, it is evident that there would be times when there was almost no pressure from the chip on the tool.
165 It is at first difficult to see how it is possible for the chip to be shearing at two or three places at the same time. It should be noted, however, that above the points T1, T2, T3, the metal of the chip is still a solid part of the forging, and moves down at the same speed as the forging in a single mass, or body, toward the lip surface of the tool; and with sufficient force to cause each of the three sections of the chip to flow or spread out at the same time at the parts indicated by the three letters F. According to the laws which govern shearing, rupture or cleavage in each case must take place as soon as the maximum possibility for flowing has been reached, and in each case shearing must occur at the left of the zone where the metal is flowing.
166 It is probable that after the shearing action has progressed in section 3 to about the point indicated by Ta, that the whole of this section gives way or shears with a rather sudden yielding of the metal from T, , to the upper surface of the chip. It is this rather sudden shearing point which undoubtedly causes the wavelike diminution in the pressure of the chip indicated in Dr. Nicolson’s experiments, referred to in paragraph 316.
167 By suddenly stopping one of our standard tools when cutting at full speed, we have clearly seen this shearing action taking place at two sections of the chip at the same time, and rupture had not completely taken place at the extreme upper part of the third section. In making an observation of this kind great care must be taken before stopping the lathe to be sure that in the tool to be observed there is not the slightest tendency to chatter, and the lathe driving parts should be massive in proportion to the sized cut being taken, as other- wise the elasticity left in the driving shafts causes an abnormal action of the tool at the instant the work stops, and produces a chip, of thicker section than the normal, which is completely severed from the body of the metal.
168 While the proportions of the chip and the section into which it is broken are fairly true representations of fact, yet it must be borne in mind that the lines illustrating the strains to which the chips are submitted, as well as the progress made in the shearing of the chip, are merely submitted as illustrating a theory advanced by us to explain the facts. We are, however, more or less suspicious of all theories, our own as well as those of others.
169 Throughout this paper the important facts stated by us have been verified by many and carefully made experiments; and we therefore trust that our readers, if unable to accept our theories, will at least have respect for our facts.
ACTION OF CUTTING EDGE OF TOOL IS THAT OF SCRAPING - CUTTING EDGE NOT UNDER HEAVY PRESSURE
170 It would appear that the chip is torn off from the forging at a point appreciably above the cutting edge of the tool and this tearing action leaves the forging in all cases more or less jagged or irregular at the exact spot where the chip is pulled away from the forging, as shown to the left of T1. An instant later the line of the cutting edge, or more correctly speaking, the portion of the lip surface immediately adjoining the cutting edge, comes in contact with these slight irregularities left on the forging owing to the tearing action, and shears these lumps off, so as to leave the receding flank of the forging comparatively smooth.
171 Thus in this tearing action, particularly in the case of cutting a thick shaving, while the cutting edge of the tool is continually in action, scraping or shearing off or rubbing away these small irregularities left on the forging, yet that portion of the lip surface close to the cutting edge constantly receives much less pressure from the chip than the same surface receives at a slight distance away from the cutting edge. This allows the tool to run at higher cutting speeds than would be possible if the cutting edge received the same pressure as does the lip surface close to it.
172 There are many phenomena which indicate this tearing action of the tool. For example, it is an everyday occurrence to see cutting tools which have been running close to their maximum speeds and which have been under cut for a considerable length of time, guttered out at a little distance back of the cutting edge, as shown in Folder 3, Fig. 17e. The wear in this spot indicates that the pressure of the chip has been most severe at a little distance back from the edge.
173 Still another manner in which in many cases the tearing action of the tool is indicated is illustrated in Folder 3, Fig. 17a, in which a small mass of metal D is shown to be stuck fast to the lip surface of the tool after it has completed its work and been removed from the lathe. When broken off, however, and carefully examined, this mass will be found to consist of a great number of small particles which have been cut or scraped off of the forging, as above described, by the cutting edge of the tool. They are then pressed down into a dense little pile of compacted particles of steel or dust stuck together and to the lip surface of the tool almost as if they had been welded. In the case of the modern high speed tools, when this little mass of dust or particles is removed from the upper surface of the tool, the cutting edge will in most cases be found to be about as sharp as ever, and the lip surface adjacent to it when closely examined will show in many cases the scratches left by the emery wheel from the original grinding of the tool.
174 With roughing tools made from old fashioned tempered steel, however, and which have been speeded close to their “standard speeds," in most cases after removing this “dust pile” from the lip surface, the cutting edge of the tool will be found to be distinctly rounded over. And in cases where the tool has been cutting a very thick shaving, the edge will be very greatly rounded over, as shown in the enlarged view of the nose of a tool in Folder 7, Fig. 41.
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‘For further evidence that the chip is torn away from the body of the forging somewhat as shown at T,, see paragraphs 170-174.
Updated on 28 May 2020, 30 June 2019
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