Most applications for a drilling jig will of course be more complex than the single
bush shown above but will range from the quite simple to the very complex. They will
also come in very many forms with two factors particularly having an impact on this.
Obviously, the greater the number of parts to be made using it the greater is the
justification for making a more complex jig that will better achieve the aims, typically,
productivity and accuracy. Secondly, and the one that cannot be covered in detail
here is the very wide range of workpiece shapes that exist. Because of this, only
some pointers in their use can be covered.
Having chosen to consider a drilling jig for the part being made there are three
factors that have to be decided upon.
First, will the jig simply be a flat plate requiring external devices to position
and hold it in place, or will it be complete with provisions for locating and clamping
the part into the jig.
Secondly, will the jig just mark out the position of the holes using a smaller drill
than the holes ultimately required, or will it enable the holes sizes required to
be drilled directly.
Thirdly, is the drill to be guided just by the plate with which the jig is made or
are hardened bushes to fitted.
Whilst the above cover the basic design of the jig there is a forth decision that
needs to be addressed, that is, what level of precision is required in the hole placing?
I should add at this stage that my comments relate to drilling what are essentially
flat items, beyond that workpieces could range from a simple bracket to complex shaped
Flat plate jig
The simplest form of flat plate jig will be to use the first one of a batch of parts
being made as a template to position the holes in the remaining ones. This is relatively
straight forward but if the part is quite thin and has large holes, say 10mm diameter
into 4mm thick, then it should be used solely to mark out the hole positions using
a smaller drill, say 3mm diameter.