Notes From
Jigs and Fixture Design by Franklin D. Jones
1920
CHAPTER XIV
PROVIDING FOR UPKEEP IN DESIGNING JIGS
AND FIXTURES
It is important to include features for upkeep in the design of the various types of fixtures used in manufacturing work.
In many cases provision for upkeep can be incorporated in the design without increasing the first cost of the fixture to any great extent, while in some instances considerable extra outlay may be necessary. Much depends upon the accuracy required in the finished product and the number of pieces which are to be machined. For example, in gun work, when great quantities of parts are to be produced, no expense is spared in making the fixtures in as durable a manner as possible, and in making provision for the replacement of worn locating points, etc. On machine tool work,
however, discretion must be exercised, so that the expense of fixtures may be consistent with the required rate of production and accuracy of the work.
Many factors influence design in this regard. The size and general character of the work determine the type of machine on which the fixture is to be used, and, therefore, the need for stability and strength. The number of pieces to be machined is a factor which must be considered, for it is apparent that a small number does not require any special care to be taken in regard to the matter of upkeep.
In drill jig work, the locating points, bushings, and feet may be made so that they can be
readily replaced when abuse or wear of these parts tends to cause imperfect work. The probable necessity for replacements is naturally determined by the rate of production that is required.
Jigs and fixtures are often handled roughly and they should be constructed to withstand such usage.
Milling fixtures are frequently required to stand very heavy cutting so that great rigidity is an important feature in their construction. In the case of horizontal turret lathe fixtures or others which revolve about a fixed center, it may frequently be found desirable to make locating rings, points, or surfaces in such a way that adjustment can conveniently be made about this center.
Points Pertaining to Upkeep. A few noteworthy points of
construction are given herewith:
1. Location of the work.
This is of primary importance and the various fixed points
provided in the fixture should be made in such a way that they
can either be readily replaced or adjusted, according to cir
cumstances.
2. The number of pieces to be machined should
receive proper consideration in the design, both in regard to
cost of the fixture and in regard to probable necessity of replacements.
3. Weight and rigidity of the fixture. This point
is naturally somewhat dependent upon the class of work for
which it is intended, and the convenience of handling.
4. Gibs.
In the case of indexing or sliding fixtures, suitable provision
should be made for adjustment by means of gibs or straps, in
order that natural wear may be taken up.
5. Revolving fixtures.
Fixtures which revolve about a fixed center, if subjected
to hard usage or if used for a great number of pieces, may be
advantageously provided with means of adjustment about the
center of revolution. This is a refinement that is very infrequently
used, and it is not necessary in the majority of cases
unless extreme accuracy is required.
Jigs and Fixture Design by Franklin D. Jones
1920
CHAPTER XIV
PROVIDING FOR UPKEEP IN DESIGNING JIGS
AND FIXTURES
It is important to include features for upkeep in the design of the various types of fixtures used in manufacturing work.
In many cases provision for upkeep can be incorporated in the design without increasing the first cost of the fixture to any great extent, while in some instances considerable extra outlay may be necessary. Much depends upon the accuracy required in the finished product and the number of pieces which are to be machined. For example, in gun work, when great quantities of parts are to be produced, no expense is spared in making the fixtures in as durable a manner as possible, and in making provision for the replacement of worn locating points, etc. On machine tool work,
however, discretion must be exercised, so that the expense of fixtures may be consistent with the required rate of production and accuracy of the work.
Many factors influence design in this regard. The size and general character of the work determine the type of machine on which the fixture is to be used, and, therefore, the need for stability and strength. The number of pieces to be machined is a factor which must be considered, for it is apparent that a small number does not require any special care to be taken in regard to the matter of upkeep.
In drill jig work, the locating points, bushings, and feet may be made so that they can be
readily replaced when abuse or wear of these parts tends to cause imperfect work. The probable necessity for replacements is naturally determined by the rate of production that is required.
Jigs and fixtures are often handled roughly and they should be constructed to withstand such usage.
Milling fixtures are frequently required to stand very heavy cutting so that great rigidity is an important feature in their construction. In the case of horizontal turret lathe fixtures or others which revolve about a fixed center, it may frequently be found desirable to make locating rings, points, or surfaces in such a way that adjustment can conveniently be made about this center.
Points Pertaining to Upkeep. A few noteworthy points of
construction are given herewith:
1. Location of the work.
This is of primary importance and the various fixed points
provided in the fixture should be made in such a way that they
can either be readily replaced or adjusted, according to cir
cumstances.
2. The number of pieces to be machined should
receive proper consideration in the design, both in regard to
cost of the fixture and in regard to probable necessity of replacements.
3. Weight and rigidity of the fixture. This point
is naturally somewhat dependent upon the class of work for
which it is intended, and the convenience of handling.
4. Gibs.
In the case of indexing or sliding fixtures, suitable provision
should be made for adjustment by means of gibs or straps, in
order that natural wear may be taken up.
5. Revolving fixtures.
Fixtures which revolve about a fixed center, if subjected
to hard usage or if used for a great number of pieces, may be
advantageously provided with means of adjustment about the
center of revolution. This is a refinement that is very infrequently
used, and it is not necessary in the majority of cases
unless extreme accuracy is required.
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