Using a drilling jig can be for one of a number of reasons, typically if access to
the area to be drilled is limited making it difficult to mark out the position of
the hole to be drilled. Photos 1 and 2 being examples where a simple drill bush made
the task easy. The task in photograph 2 also required the hole being drilled to
line up with a hole in the final assembly.
Close examination of Photo 3 shows that recesses have been made on the jig, rather
like a round tee nut. The recesses sit between the channel in the workpiece ensuring
that the hole drilled is central. The diameter was chosen so that if it were aligned
with the edge of the workpiece the hole will be the correct distance from its edge.
The larger diameter also ensures that there is more for the clamp to grip. The holes
were for the fixings for the arms on fixed and travelling steadies, the jig therefore
having been used five times. LINK
Another purpose is where holes in two or more part have holes that must line up in
the final assembly. Photo 4 shows a jig for achieving this in the case of a cylinder
and end covers. Photo 5 shows the end of the cylinder being drilled with the jig
positioned and secured by using the larger part in photograph 4. Photo 6 shows it
being used for one of the end covers and Photo 7 the end result. LINK
A third example is where a number of identical parts have to be made and a jig will
speed up the task. However, for the parts in Photo 8 (12 being made) there is an
additional reason. Even a slight error in the position of a hole to the edges, or
to the end, would be very apparent on something so narrow and not visually acceptable
in the final assembly, Photo 9.
The jig for these is seen in Photo 10 and was made using the X and Y dials on the
milling machine to accurately position the 9 holes required. The task of drilling
the 12 parts was then very easy.
Photo 11 shows a very special jig. In this case the component being made (the round
item in the photograph)required a partial thread on its outer edge. The hole was
therefore drilled as the photograph shows and then tapped.
The component can be seen in Photo 12 but after further operations had been carried
out. The partial thread in the workpiece and the jig can be clearly seen in the larger