Gloster Tooling shows semi finished 120 mm ones for £44. Dunno about tax and postage. Only dealings I've had with Gloster were for 5C collets which were decent quality and value.

Rotagrip site doesn't give me prices for semi finished ones. Bought a semi finished D1-4 for a PB chuck from them many (15+?) years ago which has been fine. Not cheapest, about 1/3 rd price of official PB one, but decent value from folk I trusted after previous dealings. Bottom price feeding on tooling those days could be very, very risky.

Surprised that Warco supplied you with some that flat out did not fit.

Clive.

They're not that difficult to make – assuming you've got one to fit a chuck to! I made two and fitted studs from RDG. I can't now recall whether or not they were some funny UNF size or M10 x 1, but probably best to get the studs first. Yes you can make those too, but for the price, I thought buying them the best option.

As far as pin threads for DIY are concerned perm one from 7/16" UNF, 7/16" BSF, 10mm x 1 or 10mm x1.25.

RDG usually have them around the £20 – £25 mark for a set of three would make sense to buy at that price if you only needed one set. Getting spendy for four though. However other common suspect suppliers want around £20 each!. Allegedly not that tricky to do but needs a decent jig and proper set-up to machine the cut out. When I looked into it, for D1-5 pins which are hard to find, plan A was to screw the cylindrical blank into a suitable chunk of metal held in the milling vice so all the cut outs were timed the same relative to the thread.

Main issue with making backplate is getting the taper depth relative to the flat back just so. Tolerances are pretty tight for Home Shop Guy. My plan was to make a gauge with an over length taper and measuring reference flange a suitable distance from where the backplate surface ought to be. Idea was to start off with an over thick bang for the backplate and machine the taper a bit too deep. Comparing the measured distance between the gauge flange on a known good backplate with the part made one would tell you how much to face off the backplate rear surface for proper fit. Ought to work provided the gauge were presented dead in line. I imagine pushing on a centre hole in the rear of the gauge with a dead centre in the tailstock should ensure alignment.

A plausible alternative would be to make the taper in a separate plain diameter part loctited into a matching bore in the home made backplate. Pushing the taper carrier into place with everything assembled onto the machine ought to get the longitudinal position right.

One thing I never did figure out was how to ensure that the tapped holes in the backplate for the studs had the threads in correct rotational tolerance. Thought that if the threads started at different angles the cut-outs could end up at the wrong distances from the back so the locks could never all pull up. Never figured the geometry out though so perhaps a 1 thread pitch error isn't enough to take the camlock out of the 1/4 turn safe range.

Clive.