Harold Hall


For a small batch, say 10 to 25 off, then making basically the same part but out of thicker material should enable the 10mm hole to be drilled through the template directly. A plate thickness equal to, or greater than, the largest hole diameter should be aimed at.


At what stage you start to used hardened bushes will of course depend on many factors and is therefore impossible to give a precise ruling. Typically, with the jig having a 10mm thick plate, 200 or more holes at 4mm diameter may be perfectly acceptable. However, at 10mm anything in excess of the 25 mentioned above may be a problem. This would certainly be the case if the drill chuck was not that accurate and the end of the drill did not run true, in this case the soft jig plate would soon be opened up.


The above methods do of course depend on the number and position of the holes being such that adding clamps can be done without blocking out the position of some of the holes. You could of course drill some holes and then move one of the clamps to enable more to be drilled but this is rather messy and only acceptable for a very small quantity of parts.


A useful form of clamp for the process are the non standard form of toolmaker’s clamp, Photograph 4 and in use in Photograph 5. The process shown does rely on the hole sizes being small enough for the assembly to be safely hand held. However, this form of toolmakers clamp does enable table clamps to be applied as Photograph 6 shows. I used the term non standard for these clamps as to my knowledge there is only one company that makes them available commercially, that is, Arrand Engineering, UK (no website).


The flat plate jig approach is particularly appropriate where large (say wider than 75mm) flat components are to be drilled in smallish quantities. In this case, making a more complex jig would be expensive and only appropriate where large quantities are involved.


A variation of this type of jig worth considering is to make a larger plate and fit pins or screws around the edge to locate it onto the part being drilled, see Sk. 2. Clamps, such as those in Photograph 5 would still be necessary.


Two Part Jigs

I use the term two-part loosely meaning a jig with top and a base, locating posts, clamps and bushes, would add other parts. These have considerable benefits over the top plate only jig but are of course more complex to make and in most cases only applicable where larger quantities are to be made. However, this may not always be the case and necessity may dictate otherwise.


Workshop Processes

Toolmakers clamps
Toolmakers clamps, using
Toolmakers clamps using