Hi All

I have just joined so thanks for having me, first off I must come clean and say that I am not a model engineer. My interest is riding motorbikes, general messing around with motorbikes and motorbike restoration. I have a Boxford VSL lathe circa 1972/76 which is a sort of a Boxford AUD with a variable speed drive and a L00 taper chuck mount. I put the lathe to good use making bits for my bikes and tend to mostly use stainless of one sort or another.
I am currently making a backplate for a 4 jaw independent chuck, I have machined the receiver and after much measuring, worrying and remeasuring it has come out good. I cut the receiver as close as possible to the same depth as the recess in the chuck which is 2.5mm It is a second hand chuck which came with a back plate for a different lathe that I have removed. On measuring the cut for the receiver on the old back plate it is 3mm in depth. This would obviously give a much more positive fit of the inner part of the backplate to the part of the chuck were the locating bolts fit , but leave a 0.5mm gap between chuck and back plate at the outer edge. My question is what is the correct or best way for a backplate/chuck to fit. I do not feel I see any chucks with a gap between them and the backplate. Thanks for any help

Hi

Thanks for everyones advice, So obviously the old back plate was incorrect. I will get the job finished off now, I left everything set up in the lathe so will make sure I have a slight clearance between spigot and rear of the chuck recess. Then on to the drilling of the 4 holes for the location bolts, I think I am going to try the grub screws turned to a point method, but will see once I get to it.

Also does anyone know where I can get a Hexagon chuck key for a Pratt chuck, I would say the size is around 17/64

I have looked at quite a few sites but they only seem to have square chuck keys.

Thanks Kevin

Hi

Big thanks for your interest and all the helpful advice that has been given, such a good response.. Thanks Chris for your generous offer to make a chuck key if required.
I have now taken a very fine skim off the face of the back plate spigot and now have a good fit with no gap at the edge, so that’s that bit done. The back plate is now out of the lathe and so the drilling of the locating bolts to think about now. I Have had to order the bolts (5/16 UNC) as I need to use socket head bolts because the holes are going to be very close to the sides of L00 mounting boss on the back plate.
Re the chuck key, the size is as suggested between sizes at around 6.5mm. The hexagonal sockets in the chuck are a bit worn, probably from someone using a 1/4 or 6mm Alan key i the past. I will give rotagrip a call and if they do not have a key I think I will give grinding part of a 7mm Alan key to fit then make a T holder to hold the resized part of the Alan key..

It’s all good fun and as you say, and good experience. Plus as the choice of L00 backplates is limited the one I got was quite large so I have made lots of Swarf getting it to size. 😅🙈
I will post an update with finished job hopefully in a few days.