Drill Jigs Principles of Design Machinery ... - Evenfall Studios

CHAPTER V
USING JIGS TO BEST ADVANTAGE*
It may be deemed proper, in the closing chapter, to review, in general
outlines, the principles of jig design, and to give some directions
for getting the full value out of jigs.
Competition and the growing demand for machinery have necessitated
the introduction of improved tools to reduce the cost. Jig and
fixture designing has come to be a trade by itself; undoubtedly there
is no branch of the mechanical business which requires so much practical
experience as this particular line. A poorly designed tool is a
very costly thing; hundreds of dollars can be wasted in a short time
with an inferior one. On its accuracy, simplicity and quickness depend
quality and quantity, hence cost of product.
There are a number of obstacles to be overcome in accurate jig and
fixture designing. The clamping must be done quickly and without
springing the jig or the work; then provision must be made for easy
cleaning out of chips, and another very important thing is, that it
must be so constructed that it will be impossible to get the work in
the wrong way. It is important to make drilling jigs as light as
possible. To obtain lightness, just as little metal must be used as is
necessary to sustain the strain brought to bear upon the part. All
metal should be so placed as to be in line with the strains exerted
thereon; therefore, jigs should be box-shaped. The advantages obtained
are manifold, for, while they are light, they are also easily
cleaned. Some of the older manufacturers still advocate the use of
heavy drilling jigs large, cumbersome things, and slow to handle.
Their reason is that a light jig will not stand the rough handling.
While that is true in a way, there ought not to be any necessity for
such rough usage. A proper system in the shop would overcome this.
It is customary in a good many of the large shops in the Eastern
States particularly to hire green men and boys to operate the jigs and
fixtures. If it is a drilling jig, especially a small one, the gang drill is
set up for that purpose; each spindle in rotation is set up for its
respective operation. The men that set these machines are competent
machinists, and they always keep one or more machines set up for
the first one who gets out of a job. They are also responsible for the
quality and quantity of work turned out. For instance, a drill or
reamer may get roughed up and in this manner spoil the work or a
drill bushing. Therefore, it keeps the machinists in charge on a con-
stant outlook. 'The operators are provided with a gage and a sample
piece which is correct. They are instructed how to use it; also to try
every few pieces to see that they are coming like the sample. In this
manner one good man can direct the work of a dozen cheap ones.
MACHINERY, August, 1904, and February, l