There are occasions when it is necessary to stamp numbers on newly created index dials etc. and although giving a punch a clout with a hammer isnt rocket science, it is worth considering that the end result will be accurate and aesthetically pleasing.
Having used the following system to good effect, I thought I would pass on my findings which others may find interesting.
Punch Holder
I needed a means of presenting the punches to the job accurately.
I have made a Tapping/ Staking Tool from bits and pieces of available material, which has 1in. bores in the arms, photo 1. A piece of 7/8in. dia. bar was cut to length and a 1/4in. slot milled along its length, deep enough to bring the centre of the punch to the centre of the bar. Whilst still set up, another cut was taken with a slightly larger diameter cutter to a depth sufficient to trap the punch when a piece of square bar, a sliding fit in the second slot, was pressed down onto the punch.
This piece of bar was drilled with two pockets to accommodate two small springs. I happened to have a piece of 1in. dia. tube which was a tight fit on the 7/8in. bar and this was used to hold everything together. The square insert was given a generous chamfer on one end and the springs inserted. The slotted bar was pressed onto the tube followed by the insert and springs which were compressed as the insert was pushed in.
The end with the chamfer was marked to ensure that it is fitted the right way up and this also serves as a guide as to which way round the punches are inserted, photo 2.
When I purchased my set of 1.5mm Number Punches, I tried them all out to see if there was any discrepancy in the location of the resultant impressions, there was. As the lettering on the stamps faces the user to ensure the number is correctly orientated, any adjustments were made to the opposite face.
Although most were correct, a couple needed a small amount of metal removing on an oilstone, and one needed metal adding. This was achieved by soldering a piece of feeler gauge to the offending face, photo 3.
I had an angle plate with three vertical slots in one face and two horizontal slots in the other. The side with the two slots was marked in the centre of the face, with the vertical line extended deeply to the top, and this line carried across the top. A 3/8in. hole was drilled and reamed at the marked centre, photo 4.
As I was only making dials for a Cowells and a Prazimat lathe, the mandrel photo 5 was made with a turned shaft to fit the angle plate at one end and a shaft to fit the Cowells dials at the other. An additional bush was made to adapt the Cowells end to suit the larger bore Prazimat dials.
The angle plate was secured to the work table with an M8 coach bolt which was held captive in the table slots. This was used because there is little room to fit and swing a spanner under the table, photos 6 &7. Also the plate has to be held in position with one hand while the nut is tightened with the other.
VDH Micro Drum
As the Versatile Dividing Head is the current project, the stamping of the Micro Drum will serve to illustrate my method, photo 8.
A new mandrel was made from a piece of 3/8in. dia. Rod. It was threaded M8 at one end and turned down to a snug fit in the Drum at the other. The Drum was secured with an M4 cap screw, and the assembly mounted on the angle plate with a knurled nut, as finger tightening only is required, photo 9.
The dial was set with one of the long tens lines aligned with the scribed vertical line on the angle plate, and the 1/4in. dia. pin seen in photo 2 inserted into the holder with the point aligned with the tens line, photo 10. It is set by eye to position the number laterally. When all is set, the pin is replaced with the No.1 punch, ensuring it is correctly orientated and the punch set with a square against the angle plate and one of its sides before locking the punch holder. The springs hold the punch in position.
With feed-screw dials, the single numbers are indexed at each long line, placing the numbers at the top of each line. In this case there are double digits placed upside down to the normal orientation. With the dial tightened by hand so it is just possible to turn it with the fingers, it is aligned with the first unit line to the right of the tens line with the punch touching the work, and the No.1 stamped. As the dial is to be turned clockwise, it should remain quite tight as it is advanced to the first unit line to the left of the tens line where the 0 is stamped. The dial is turned to the subsequent unit positions and the rest of the numbers stamped finishing on double zero, photo 11
With numbers of this size, the left and right single unit spacing worked well for the number spacing. With larger number stamps, use two unit lines each side, or it is possible to sight one and a half.
Cleaning Up
The numbering could follow the graduating with the piece still in situ in the lathe with the graduation indexing system still in place, and this used to index the number positions. I dont follow this method, as it is difficult to see what is going on and I dont like the idea of subjecting my chucks and headstock bearings to hammer shocks.
If a suitable mandrel is turned to accept the dial, then following the clean up of the graduation lines with a fine finishing tool, the tool is left set and the dial removed.
Following the stamping by the above method, the dial is returned to the mandrel and another cut taken at the same setting. This should result in the tool missing the graduations and just removing the raised material around the numbers. If necessary, a further very light cut could be taken over the whole surface.
Unfortunately, I was unable to practice what I preach, as my mandrel was removed long before I stamped the numbers and wrote this. Although with a lot of fiddle the mandrel could be reused, any run-out at all would show in the fine graduation lines.
The dial was held in the bench vice with some cardboard softening, photo 12 and with the finest needle file, the burrs were removed with a few light strokes following the curve of the surface. Stop filing just clear of the main surface.
These files are formed with handles, but I find them uncomfortable to use and have made a small handle with four slits in the end which are closed slightly to grip the file. The handle is easily transferred from file to file, photo 13.
The mandrel can now be used, as any run-out will be followed by the file, which is given a dose of soluble oil after a thorough cleaning. The file is allowed to float all over the surface and the end result should be a smooth, silky finish.
After wiping off the oil, the surface is rubbed all over with a chinagraph pencil and rubbed in with an oily finger. Another wipe over and the job is done, photo 11.
For hitting all types of punches, I find the right hammer helps. I like to use an 8oz Warrington hammer with a rather short (10 inch) handle. It is ergonomic, as the hands are closer together and the weight is such that it requires very little striking force to be applied.
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