Making Slotted Nuts with a Grinding Disk

The carriage cheeks for the Armstrong 110pr cannon have 10 roughly vertical bolts which attach the wooden slides, and also bolt together the thick planks which make up the cheeks.

1. Some woodworking on the vertical mill, using a very sharp and scarey shell cutter. I used to do a lot of woodworking, but these days I use the metalworking tools at their highest speeds to do accurate cuts in wooden parts. Here milling the rebates which fit the carriage into the traversing platform of the Armstrong 110pr.

The nuts for the bolts are all at the bottom end, and are buried in the slides. In previous model cannons I have milled pockets for the nuts, and tightened the nuts with a socket spanner, but I was not happy with the large diameter of the pocket which was needed to accomodate the socket spanner.

So, this time I decided to tighten the nuts using a screw driver, having cut a slot in the surface of the nuts.

2. This is an M4 nut, with a slot cut into the surface, which will be tightened with a special screwdriver. How to cut such a tiny slot? (excuse my dirty finger. This photo was taken after several hours in the workshop.)

3. The screwdriver tip which has been modified with a Dremel, to drive the slotted nuts.

4. This is the setup for cutting the slot. the nut is screwed onto some sacrificial threaded 4mm rod. The slot is cut with a thin cutting disk, 1mm thick, mounted onto a shop made mandrel which fits into an ER40 collet on the vertical mill. A bit of fiddling with the height settings, but once it was set, making the slotted nuts was very quick and easy. The slot was 2mm deep in the 4mm deep nuts. Plenty of thread remaining to tighten the nuts.

5. Slotted nuts on the right. Ordinary unslotted nuts on the left, which cannot be tightened except by making bigger holes, or slotting the nuts, which is what I did.