Traversing Platform Floor, and Carriage Recoil Stops.

by John

Firstly some woodworking to make the platform floor. Basic machining, drilling and screwing.

Quite pleasant to do some basic cutting on the bandsaw and thicknessing on the mill. HSS metal mills give a good finish on hardwood. It was finished quickly, and went so well that I proceeded to a task which I had been putting off, because I knew that it would be very difficult.

I made the carriage recoil stops, and installed them.

The problem was that the platform had been previously assembled, including gluing of the joints. And I was not going to break those joints for anything.

The recoilatop is on the inside of the platform slides, at the rear. Shown here above the bollard. It is recessed into the slide so only the actual iron stop is above the surface. Also, it is underneath the bracket which supports the gunner’s rear platform.

The stop bracket is about 30mm x 6mm x 2mm, and the stop protrudes about 5mm further. So the first question was how to make the rebate. The distance between the slides is only 53mm. Not much space to use chisels. And end mills could not be used. The metal surface of the slides is glued and screwed to the slides, so removing those was not an option either. I should have made the rebates BEFORE I glued up the platform. Oh well….

This is the setup which I used….

I bought some Woodruff cutters and T slot cutters at a sale some years ago. So I cut the slots with one of those. The cutter worked well, but it left sloping ends. One of the ends is hidden behind a bracket, but the other one is visible. Used the inspection mirror to watch the milling on the near slide.

So how to square up those ends. Not enough room to get a chisel into that space. Still wondering, I made the actual stops.
Making the stops involved some basic milling and silver soldering. The steel nut got a bit chewed up during the slotting. It will not be visible in the final assembly.

Then, rather than squaring up the recess, I rounded the hidden corner of the stop bracket. Easy!

Drilled the holes in the stop brackets for the screws, fitted the stops into position. Now, how to drill the holes in the wooden slides for the screws? The holes in the wood were only 1.4mm diameter. And a 1.4mm drill bit is not long enough for the drill chuck to miss the other slide. To avoid the other slide the hole would be excessively angled.

So I used another trick which I have used previously. I silver soldered the drill bit into some fine (2mm OD) copper pipe….

1.4mm, 1.6mm, and 2mm drill bits given substantial extensions. I used copper for the small sizes because I had some suitably sized pipe. I had drilled the hole in the brass rod for the 2mm extension for another model.
The extension meant that there was only slight angulation of the hole when drilled with a battery drill.

I will enlarge the countersink on the stops to bury the screws deeper, then file the screws flush with the stop surface. I doubt that the bit of angulation will ever be noticed. I used steel screws, because a brass one snapped off and I had to drill through the remnants. The steel screws are slightly bigger than intended, but not excessively. I had removed the gunners platform to improve the access. The area will look tidier when fully reassembled.

I am very glad that particular task is all but finished!!

ps. I have called them “stops” but that is probably not the correct term. The recoil of the carriage is reduced by the 5º slope of the slides and the braking from the compressor. The “stops” (or whatever they are called) are the final impediment in limiting the recoil of the carriage and its barrel.