All right. Progress is being made. We hacked the Bosch using Dag83’s excellent tutorial, and printed @ned 's bushing and bracket.
Unfortunately, my 3D printed parts were not strong enough. Just the bushing, the bracket is ok so far.
The first bushing let go of the tube, so we decided to drill a hole in it and the tube and put a grub screw in. Unfortunately this weakened the bushing and it split at one of the printed layers.
So I printed another one, this one I designed myself and included a hole for a grub screw. Unfortunately when we stuck it on the tube it split again. My tolerances were obviously too tight.
So, being a Men’s Shed with a well-equipped metalwork shop we turned one out of nylon on the lathe. It is now indestructible and we can move on to the next step.
In case anyone else needs to know the dimensions to make your own:
Outer diameter 22mm
Centre hole for threaded boss diameter 10mm
Counter bore for tube diameter 15.5mm to depth 15mm
The four screw holes to attach the boss can be drilled by hand. There is 5mm of material to play with. A hole can be drilled through the side as required. We drilled a 3.2mm hole all the way through the bushing and the tube, then threaded the bushing for an M4 grub screw. The tip of the grub screw sits in the hole but doesn’t go through the tube.
Next step, calibration.