Productivity Science of Machining III - Industrial Engineering Research by Taylor Part 3

Lesson 4 of Process Industrial Engineering ONLINE Course (Module)

Lesson 47 of  Industrial Engineering ONLINE Course

IE Research by Taylor - Productivity of Machining  - Part 1 - Part 2  - Part 3  - Part 4 - Part 5 

Lesson 48 -  Productivity Science of Machining for Process Improvement Part 4.

Paper Published in the Proceedings of IISE 2020 Annual Conference.

Frameworks for Productivity Science of Machine Effort and Human Effort

Rao, Kambhampati Venkata Satya Surya Narayana. IIE Annual Conference. Proceedings; Norcross (2020): 429-434.

https://www.proquest.com/openview/5786c4e6edff56abf808b4db26f083b3/1.pdf

IE Research by Taylor - Productivity of Machining: Variables Discussed: Shape or contour of cutting edge and Cutting fluid (water)

(D) shape or contour of cutting edge: 1 to 6; 

282 (D) The shape or contour of the cutting edge of the tool, chiefly because of the effect which it has upon the thickness of the shaving.

Proportion is as  1 in a thread tool to 6 in a broad nosed cutting tool. , 

(E) copious stream of water on the tool: 1 to 1.41;

283 (E) Whether a copious stream of water or other cooling medium is used on the tool. 

Proportion is as 1 for tool running dry to 1.41 for tool cooled by a copious stream of water. 

(D) shape or contour of cutting edge: 1 to 6; 

282 (D) The shape or contour of the cutting edge of the tool, chiefly because of the effect which it has upon the thickness of the shaving.

Proportion is as  1 in a thread tool to 6 in a broad nosed cutting tool. , 

PRINCIPAL OBJECT IN HAVING THE CUTTING EDGE OF TOOLS CURVED IS TO INSURE AGAINST DAMAGE TO THE FINISHED SURFACE OF THE WORK

307 The above experiments described in paragraphs 293 to 303 upon the effect of thickness of shaving on cutting speed enable us to explain from the theoretical standpoint the well known fact that each properly designed roughing tool should have the line or contour of its cutting edge curved as it approaches the extreme nose of the tool or that portion of the tool which insures a good and true finish of the work. A tool whose cutting edge forms a curved line of necessity removes a shaving which varies in its thickness at all parts. The only type of tool which can remove a shaving of uniform thickness is one with a straight line cutting edge. The object in having the line of the cutting edge of a roughing tool curved as that part of the cutting edge which does the finishing is approached, is to thin down the shaving at this point to such an extent as will insure the finishing part of the tool remaining sharp and uninjured even although the main portion of the cutting edge may have been ruined through overheating or from some other cause.

310 It will be observed that the quality and accuracy of the finish left upon the work will depend upon maintaining sharp and uninjured throughout the cut that portion of the cutting edge of the tool which extends, say, from about point 0.005 inch to point 0.02 inch.

311 By examining the standard cutting speeds noted opposite each of the straight-edge shavings, Fig. 111, it will be seen that the standard or ruining speed at point 0.04 inch, for instance, on the curve of our enlarged tool, is 13 feet. From this it is evident, then, that if the tool enlarged in Fig. 112 were run at a cutting speed of 13 feet per minute so as to just ruin it at point 0.04 inch, the tool at point 0.01 inch would then be running at less than one-half of the cutting speed which would be required to ruin it. It would be, therefore, well within its safe limit of cutting speed, and would remain sharp and uninjured until the edge at 0.04 inch had entirely broken down. It is obvious then that a curved line cutting edge insures the finishing part of the tool from damage and for this reason the cutting edges of all tools should be curved, at least as that portion of the edge of the tool is approached which leaves the work of the proper size and with the proper finish.

TOOLS WITH BROAD NOSES HAVING FOR THEIR CUTTING EDGES CURVES OF LARGE RADIUS BEST TO USE EXCEPT FOR RISK OF CHATTER

312 Upon appreciating the increase in the cutting speed obtained through thinning down the shaving, as shown in our experiments with straight cutting edge tools, described in paragraphs 292 and 303, the tools shown on Folder 7, Figs. 32, 33, and 34, were made, and used on roughing work for years in the axle lathes of the Midvale Steel Company. The gain in cutting speed of these standard broad nosed tools over our standard round nosed tool, as shown in Folder 5, Figs. 24 and 23, is in the ratio of 1.30 :1.

313 This general shape of tool continues to be extensively used, but it is subject to the disadvantage that it is likely to cause the work to chatter, and so leave a more or less irregular finish.

314 Were it not for this difficulty, added to the fact that our standard round nosed tool has a greater all-round adaptability and convenience, the tools illustrated on Folder 7, Figs. 32 to 34, would undoubtedly be the proper shapes for shop standard. This matter will be further discussed in paragraph 665. A method is there described of using two or more broad nosed tools so as to be free from danger of chatter even upon work which is especially liable to chatter.

REASONS WHY CUTTING EDGE WITH COMPARATIVELY SMALL RADIUS OF
CURVATURE TENDS TO AVOID CHATTER

315 The avoidance of chatter in the tool plays such an important part in the design of the edge for standard tools that we quote in full from that portion of Dr. Nicolson's admirable experiments which appears to the writer to offer an explanation for one of the important causes for chatter.

316 Dr. Nicolson's experiments, which were made with special apparatus (of his own design) for weighing the pressure of the chip upon the tool, were described in his paper (published in Transactions, Vol. 25, pp. 672, 673, 674), as follows:

317 The experiments (numbered 725 to 732 inclusive), the results of which are given in Table 9 are of special interest in regard to: First, the variation of the cut ting force as the cut progresses at a very low speed; second, the variation of the cutting stresses with large ranges of speed variation.

318 These experiments were made with a tool having a 55 degree cutting and a 67 degree plan angle; a cut inch deep by inch wide being taken.

319 For numbers 725 and 726 the lathe was turned round at a cutting speed of about 1 foot in 5 hours, by means of a wire rope made fast round the large cone pulley, and hauled upon by a man operating a winch.

320 A pointer about 5 feet long was clamped upon the forging, and the four dynamometer gages were read at every half an inch of motion of the end of this pointer, i. e., at about six one-hundredths (0.0625) of an inch of the cut. The vertical force varies from 9080 to 8920 every of an inch of motion of the tool, the same wave length characterizing the variation of the surfacing and traversing forces. The observations have been plotted in Fig. 340 [see Folder 12, Fig. 86, present paper] on a base of actual relative tool motion.

REASONS FOR ADOPTING THE PARTICULAR CURVES CHOSEN FOR THE CUTTING EDGES OF OUR STANDARD TOOLS

325 Having explained the necessity for curved cutting edges in standard roughing tools, it is desirable to give our reasons for the adoption of the particular curves of our standard tools, illustrated in Folder 5, Figs. 20a to 25e, and Folder 17, Fig. 120. It will be noted that as the body of the tool becomes smaller, the radii of cur vature of the cutting edge also become correspondingly smaller. This change in the curve of the cutting edge is rendered necessary by the fact that the smaller tools are used in the small lathes, which, generally speaking, work upon small forgings, from which cuts are removed which are both shallow in depth and have comparatively fine feeds. Forgings which are small in diameter are quite as liable to chatter as the larger forgings which are machined in larger lathes, and in order to avoid this chatter, it is necessary that a curve for the cutting edge should be chosen which will give a variation relatively in the thickness of shaving even in small depths of cut. Thus, for the avoidance of chatter, the curve of the cutting edge should be small in proportion as

the depth of cut and feed which it it normally takes are small

326 As will be seen later, the smaller radius of curvature of the cutting edge involves a diminution in cutting speed. Therefore, with larger sized tools it becomes important, on the other hand, to take as large a radius of curvature for the cutting edge as is compatible with freedom from chatter. The coarser feed which usually accompanies the larger tool also calls for a larger radius of curvature at the nose of the tool, in order that the ridges left by the spiral path of the tool along the forging shall be as low as practicable.

327 The all-round adaptability of the standard tool to a variety of uses also calls for a smaller radius of curvature the smaller the tool, since standard roughing tools are continually required to run up against a shoulder or into a corner on the work, and the fillet in this corner is normally small in proportion as the forging or casting is small.

328 Generally speaking, also round nosed roughing tools of the type shown do not require the special care in adjusting in the tool post that would be demanded of tools designed with a straight line cutting edge for the purpose of producing a smooth finish, etc.

329 By comparing curves of the tools on Folder 5, Fig. 21a, with Folder 5, Fig. 21b, it will be observed that tools which are to be used for cutting cast iron and hard steel have slightly larger radii of curvature than those which are to be used for the softer steel and wrought iron. The reason for this change is that much slower cutting speeds must be used in cutting hard steels than for soft, and this is also to a less degree true for cast iron as compared with soft steel.

330 It is a matter of common experience that the slower the cut ting speed, the less the liability of the tool to chatter. It therefore becomes safe from the standpoint of chatter to use in cutting hard steel and also cast iron a larger radius of curvature than would be permissible in cutting soft steel. The fact has already been pointed out that the larger the radius of curvature, the thinner the shaving, and therefore the higher the cutting speed, and in the interest of economy, it is of course particularly desirable in cutting hard steels to increase the necessarily slow cutting speed as much as practicable.

331 For the following entirely different reason, also, the radius of curvature for tools to be used in cutting cast iron is made larger than in tools to be used in cutting soft steel. Cast iron is cut, as will be seen in paragraphs 491 and 512, with less cutting pressure or resistance to the tool than is required for soft steel. Therefore, in a given lathe a greater depth of cut and coarser feed can be taken on cast iron

than on soft steel; and, as explained above, the coarser the feed, the greater should be the radius of curvature of the extreme nose of the tool in order to leave an equally smooth finish.

332 In many machine shops a very considerable portion of the work consists of cuts to be taken upon pieces of cast iron; the depth of the cut being comparatively shallow and the strength and rigidity of the casting begin so great that in order to use even approximately the full pulling power of the lathe or planer, etc., broad feeds must be taken. In our standard shop tools, as illustrated in Folder 5, Fig. 21a, the extreme end of the noses are rounded with too small radii to take a very broad feed, and yet at the same time leave a reasonably smooth finish. It is therefore desirable in all such shops to have standard tools available which are especially designed for work of this character.

333 In Folder 5, Fig. 22, is illustrated a single size of the type of tool which we recommend ' this purpose. It will be observed that in form it corresponds exactly to our other standard tools for cutting cast iron and hard steel except that the extreme nose of the tool is widened out so as to have a curve of very large radius, approximating to a straight line.

(E) copious stream of water on the tool: 1 to 1.41;


COOLING THE TOOL WITH  HEAVY STREAM OF WATER  UPON THE CUTTING SPEED or POURING A HEAVY STREAM OF _WATER UPON  THE CUTTING EDGE OF  THE TOOL

593 Cooling the nose of a tool by throwing a heavy stream of water or other fluid directly upon the chip at the point where it is being removed by the tool from the steel forging enables the operator to increase his cutting speed about 40 per cent.‘  In spite of the fact that (as a result of our experiments) the whole machine shop of the Midvale Steel Company was especially designed as long ago as 1893 for the use Of a heavy stream of water (super-saturated with soda to prevent rusting) upon each cutting tool, until very recently practically no other shops in this country have been similarly equipped.

594 It is indeed a matter of wonder that this element has been entirely neglected.

595 The following are the important conclusions arrived at as to the effect on the cutting speed of cooling the tool with a heavy stream of water.

596 (A) On Folder 15, Table 110, are summarized the results of our experiments upon the gain in cutting speed through the use of a heavy stream of water on the tool in cutting different qualities of metals with varying types of tools, namely, modern high speed chromium-tungsten tools, heated to the melting point, the old fashioned self-hardening tools, and carbon tempered tools.

597 The results obtained with modern high speed tools are the only ones of great practical interest at present, since no well managed machine shop would use any other than high speed cutting tools. The other data, however, are given as a matter of record and historic interest. (See paragraph 631)

598 (B) With high speed tools a gain of 40 per cent can be made in cutting steel or wrought iron by throwing in the most advantageous manner a heavy stream of water upon the tool.

599 In designing slide rules or tables, etc., for assigning daily tasks to machinists a 33 per cent increase in cutting steel or wrought iron should be allowed for instead of 40 per cent, owing to the fact that workmen are more or less careless in directing the stream of water to the proper spot upon the tool.

600 (C) A heavy stream of water (3 gallons per minute) for a 2-inch by 2-inch tool and a smaller quantity as the tool grows smaller, should be thrown directly upon the chip at the point where it is being removed from the forging by the tool. Water thrown upon any other part of the tool or the forging is much less efficient. (See paragraphs 607 to 609)' .

601 (D) The gain in cutting speed through the use of water on the tool is practically the same for all qualities of steel from the softest to the hardest.

602 (E) The percentage of gain in cutting speed through the use of water on the tool is practically the same whether thin or thick chips are being removed by the tool. (See paragraph 630)

603 (F) With modern high speed tools a gain of 16 per cent can  be made by throwing a heavy stream of water on the chip in cutting CAST Iron. (See paragraphs 625 to 627)

604 (G) To get the proper economy from the use of water in cooling the tool, the machine shop should be especially designed and the machine tools especially set with a view to the proper and convenient use of water. (See paragraphs 610 to 616)

605 (H) In cutting steel, the better the quality of tool steel, the greater the percentage of gain through the use of a heavy stream of water thrown directly upon the chip at the point where it is being removed from the forging by the tool. The gain for the different types of tools in cutting steel is: a Modern high speed tools 40 per cent; b Old style self-hardening tools 33 per cent; c Carbon tempered tools 25 per cent.

606 This fact, stated in different form,is that: The hotter the nose of the tool becomes through the friction of the chip, the greater is the percentage of gain through the use of water on the tool. (paragraph 631) 

THE PORTION OF THE TOOL ON WHICH THE WATER JET SHOULD BE THROWN

607 A series of experiments has demonstrated that water thrown directly upon the chip at the point where it is being removed from the forging by the tool will give higher cutting speeds than if used in any other way.

608 As another illustration of the small value to be attached to theories which have not been proved, we would cite the following: After deciding to try experiments upon the cooling effect of water when used upon a tool, it was our judgment that if a stream of water were thrown upward between the clearance flank of the tool and the forging itself in this way the water would reach almost to the cutting edge of the tool at the part where it most requires cooling, and that, by this means the maximum cooling effect of the water would be realized. We, therefore, arranged for a strong water jet to be thrown, as shown on Folder 7, Fig. 40b, between the clearance flank of the tool and the flank of the forging, and made a series of experiments to determine the cooling effect of water with various feeds and depths of cut. So confident were we of the truth of this theory that we did not deem it worth while to experiment with throwing streams of water in any other way, until months afterward, when upon throwing a stream of water upon the chip directly at the point where it is being removed from the forging by the tool, we found a material increase in the cutting speed, and thus our first experiments were rendered valueless.

609 Practically, great difficulty will be found in getting machinists in the average shop to direct the stream of water on to the chip in the proper way as indicated on Folder 7, Fig.40a, because when a sufficiently heavy stream of water is thrown upon the work at this point it splashes much more than when thrown upon the forging just above the chip; and the machinists prefer slower cutting speeds and less splash. However, when they are managed under the “task system” with trained speed bosses who are accustomed to obeying orders, this trouble disappears. 

FORTY PER CENT GAIN IN CUTTING SPEED FROM THROWING A HEAVY STREAM OF WATER UPON THE TOOL IN CUTTING STEEL

610 It has been customary for many years to use under certain circumstances, a small trickling stream of water upon cutting tools (mostly on finishing tools, and with the object of giving the work what is called a “water finish”). For this purpose a small water can is generally mounted upon the saddle of the machine above the tool, and refilled from time to time by the machinist. Such streams of water, however, have little or no effect in increasing the cutting speed because they are too small in volume to appreciably cool the nose of the tool.

611 The most satisfactory results are obtained from a stream of water falling at rather slow velocity, but with large volume, at the proper point upon the tool; since a stream of this sort covers a larger area of the tool and is much freer from splash.

612 This water supply should be delivered through pipes fitted up with universal friction joints, so that the apparatus can be quickly adjusted to deliver the water at any desired point (the pipe being supported by a rigid bracket attached to the saddle of the lathe, preferably on the back side so as to be out of the way). In the case of short lathe beds the water supply can be delivered from overhead through a rubber hose, and in the case of long lathe beds through telescoping pipes attached to the saddle (smooth drawn "brass pipes telescoping inside of ordinary wrought iron pipes, with suitable stuffing boxes being used).

613 About three gallons of water per minute are required for adequately cooling a very large roughing tool, say, 2 inches by 2 inches section; and proportionally smaller quantities as the tool grows smaller.

 614 For economy, the same water should be used over and over again, and it should be supersaturated with soda to prevent the machines from rusting. Wrought iron pipes about 1- inches diameter should lead the water from beneath the machine below the floor to the main soda water drains at the side of the shop. These drains are made of pipe from 3 to 5 inches in diameter, with a chain extending through them from one end to the other, the chain being twice as long as the drain through which it extends. In case of sediment forming in this pipe or in case of chips passing by the double sets of screens and double settling pots which should be supplied at each machine, the drain can be quickly cleaned by pulling the chain backward and forward through it once or twice.

615 The soda water is returned through this system of underground piping to a large central underground tank, from which it is pumped through a small, positive, continuously running pump, driven by the main line of shafting, into an overhead tank with overflow which keeps the overhead soda water supply mains continually filled and under a uniform head. If the shop is constructed with a concrete floor, a catch basin for the water can be molded in the concrete directly beneath each machine. Otherwise, each machine should be set in a large wrought iron pan or shallow receptacle which catches the Soda water and the chips. In both cases, however, two successive settling pots—independently screened so as to prevent the chips, as far as possible, from getting into the return main—are required beneath each machine. 

616 The ends of the 1-inch wrought iron pipes which lead the water from the machines to a large drain at the side of the shop should be curved up with a sweeping curve so that their outer ends come Close to the top of the floor of the shop. The sediment and chips must be cleaned from these pipes from time to time by means of a long round steel rod from § to 1 inch in diameter, which, after removing the plug at the outer end of the drain pipes, is shoved through the pipe. Apparatus of this type has been in successful use for about 23 years with no trouble from clogging.

DETAILS OF TYPICAL EXPERIMENT FOR DETERMINING GAIN THROUGH HEAVY STREAM OF WATER ON THE TOOL

617 The following is a detailed description of one of our series of Experiments on the effect of water on the tool, made in this case for the purpose of determining the gain from the use of a. heavy stream Of water in cutting an exceedingly hard bar of metal, especially made and hammer hardened so as to be harder than hard steel of any of the qualities usually met with in machine shop practice. This experiment is given in detail as a type of our best method of experimenting in cases of this kind. The following are the physical tests and the chemical composition of the steel bar experimented upon. 

This bar was hammer hardened.

618 Tools of the shape shown on Folder 5, _Fig. 24, were made from tool steel of the following chemical composition, and were treated by the Taylor-White process (11. e., heated to the melting point, cooled down, and reheated to 1150 degrees in a lead bath): 

They were then all standardized to prove their uniformity by being run at a cutting speed of 16 feet per minute, duration of cut 20 minutes, feed ,1; inch, depth of cut T“; inch. The ruining speed upon this forging of tools of this type had been previously proved to be between 16 and 17 feet per minute. The following are the details of the experiments with water:




619 From the list given above are below extracted those experiments that show the highest speed at which each tool endured 20 minutes and also the length of time it endured before ruining at one foot higher speed.



EXPERIMENTS WITH WATER

620 In test No. 261 b tool V. had been ruined at a speed of 24 feet and thereby, owing undoubtedly to being overheated by the friction of the chip, as was afterward ascertained, suffered a marked deterioration. This accounts for the lower maximum speed at which it subsequently stood up.

621 In order to fully ascertain whether the ruining of these tools while running with a heavy stream of water to try to keep them cool had any marked injurious effect upon them, the following tests were made without the use of water on the second day of the experiments:

622 The average cutting speeds of the U tools (all of which were proved to be uninjured) were as follows: 22 + 22 + 23 ~ —3~ —~-=22.33 feet, which divided by 16 feet gives 1.416 to 1.0 as the gain made by using water on the tool.

624 Taylor-White tools similar to those described above, having been carefully standardized, showed a cutting speed when run without water of 60 feet per minute, and when run under a heavy stream of water of 83 feet, thus indicating a gain of 1.39 to 1.0 from the use of water. The average gain then through the use of water on the tool for hard and soft forgings is about 40 per cent.

SIXTEEN PER CENT GAIN IN CUTTING SPEED FROM THROWING A HEAVY STREAM OF WATER UPON THE TOOL IN CUTTING CAST IRON

625 In 1906 after the writing of this paper was well under way it occurred to us that we had accepted as true without verification through accurate experiments the fact that water could not be used in cutting cast iron. This is another of the many instances in which an absolutely erroneous opinion prevails throughout all of our machine shops without any foundation in fact. It is likely, however, that this opinion has become so firmly rooted in the minds of all mechanics and foremen from the fact that a water finish cannot be made on cast iron, while it is in many cases most desirable for steel.

626 To determine the effect of a heavy stream of water in cooling a tool cutting cast iron, experiments (similar to those described above) were made by us during the summer and fall of 1906 on a test piece consisting of exceedingly hard cast iron with cutting tools of three different chemical compositions. The piece of cast iron is the same as that marked “hard cast iron" on Folder 20, Table 138.

627 The chemical composition of three of the latest high speed tools experimented with was that of tools Nos. 2, 5 and 7 (Folder 20, Table 138). The following table represents the average gain made by these tools when they were run with a heavy stream of water as compared with running under exactly the same conditions dry. 

Depth of cut   fig inch, feed   fg inch, standard 20-minute cut; tools used, our standard 1"; inch (shown Folder 5, Fig. 24)

Cutting speed without water . . . . . . . . . . . . . . . . . .47 ft.
Cutting speed with heavy stream of water . . .54 ft. 7 ins.
Gain through use of water . . . . . . . . . . . . . . .16 per cent

628 Since writing the section of the paper covering the whole subject of the gain by cooling the tool with water, we have again met in our experiments with one of the strange. anomalies which characterize the laws governing the art of cutting metals.

629 When the best of the modern high speed tools, namely, tool No. 1, Folder 20, Table 138, was run with a heavy stream of water in cutting the hard forging referred to in the same table, it was shown that instead of a gain of 41 per cent through the use of water, as had been obtained with tools differing in their chemical composition, as referred to in paragraphs 610 to 630, there was a gain through the use of water of only 15 per cent. A lack of time prevented our going more fully into the effect of water upon high speed steels of the most modern composition with medium and soft forgings. It is, therefore, manifestly of the greatest importance to carry on thorough experiments in this field. Our experiments with tool No. 1 gave the following data: 

Depth of Cut 13; Inch. Feed 11; Inch." Standard 20-minute cut.

Cutting speed without water . . . . . . . . . . . . . .41 ft. 5 in.
Cutting speed with water . . . . . . . . . . . . . . . . . .47 ft. 8 in.
Gain through use of water . . . . . . . . . . . . . . .15 per cent


THE PERCENTAGE OF GAIN THE SAME WHETHER THIN OR THICK CHIPS ARE BEING REMOVED

630 When in the Midvale Steel Works the gain in cutting speed through the use of water on the tool was discovered in 1884, a thorough investigation was made with varying depths of out and thickness of feed—carbon tempered tools being used in cutting steel tires —and it was found that the percentage of gain in cutting speed through the use of water was the same whether the chips were thick or thin. These experiments have not been repeated by us with high speed tools, and it is possible that, owing to the very great difference in the heat of the high speed and the carbon tempered tools, there is a different ratio of gain for thick and thin chips with high speed tools. However, our slide rules have been in practical use in cutting chips of all degrees of thickness for years, using water on the tool, with the same ratio of increase in speed for thick and thin chips; and it would seem if any material difference exists between the gain in thick and thin chips, that this fact would have become evident through the failure of our slide rules to indicate the proper speeds. A careful experiment on this point is desirable.

631 In 1894—95 experiments were made with a carbon tempered tool containing 1.6 per cent chromium and with tools made from old fashioned self-hardening Midvale steel, of the following chemical composition:


632 The carbon tempered tools showed an average gain of 25 per cent in cutting a hard steel forging of the following physical and chemical properties:

The Mushet and Midvale self-hardening tools showed an average gain of 30 per cent in cutting the same forging. From these figures it will be noted that as the cutting speeds of tools grow higher, the percentage of gain through the use of water for cooling the tool grows greater. This would seem to be due to the fact that (taking the two extremes) the noses of the modern high speed tools are very much hotter under the great friction caused by the high speed of the chip than are the old fashioned tempered tools with their slow speeds, and that therefore the water acts in a considerably more efficient manner in cooling the high speed tools than the slow speed tools.


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Updated on 16 July 2021

Pub 2 July 2020