You may be able to punch (for example) a nice even ring of numbers on a vernier dial freehand, I'm afraid I don't have that skill. So I made this little guide to help keep the punch aligned and square to the work. Construction is obvious from the picture (I hope) which shows that I use a standard magnetic base to hold the guide. This is particularly useful because it can be set up on the lathe or milling machine bed in just the right position - and it stays there.
Clamp the bushes in place using a toolmakers clamp in the 3/4" section bms, and at the point shown in the diagram drill and ream the 1/2" diameter holes for both the column and the punch guide. The clamp will hold the bush firmly whilst the 1/2" hole is cut partly into the bms and partly into the brass bush. Remove the bushes and saw (or part in the lathe) in the middle of the semi-circular cut-out made by the 1/2" hole. Mark the parts so they go back in the same place. Use either a 1/4" BSF allen screw or make t-bolts to fit the bushes. Only light tightening will be required to clamp the 3/4" firmly in position using this method.
To make the punch-guide you need a round piece of brass (5/8" is fine), again leaving a collar full diameter. Problem is that you need a neat 1/4" square hole (size of the punch) in the middle of it. Easiest way of achieving this is to mill a 1/4" slot all the way along the 5/8" brass rod, then silver solder a piece in to fill the gap but leaving the 1/4" hole. Turn to shape after this has been done.
That's all there is to it. Now there's no excuse for un-even number punching!
(c) Chris Heapy 1996.
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