You probably need to ring round steel stock holders to see if they will cut a slug of BMS or Cast Iron of approximatly the right size for the back plate.

regards

RDG do them but currently out of stock. Maybe a phonecall could shed some light on when available.

Me, can you confirm if you just want an unmachined casting or billet to make your own from scratch or a L00 backplate that is part machined eg thread and taper cut so you just need to cut the register. Until you cut the taper it does not become an L00 backplate and could be used for anything though you will need one with a larger boss than the usual Myford blank castings.

If it's just a billet, M-machine will cut you grey or SG Iron or you could get EN3 from someone like Steelcitygav on e-bay.

That looks about right Dave. The L00 thread is i believe 3-3/4 x 6 so it looks as though there is enough meat there. It may be a little bit tight on the taper length though after cleaning up.

regards

It's not a backplate that I would like to tackle making. To get the taper right, I would get a dti set exactly on the centre line and run it against the nose taper of the spindle to set the compound. That is the most critical part, the threads are easier. Google for drawings of the L00 size. You will probably have to get a cut length of cast iron of slightly bigger than your chuck diameter and drill and tap it to hold it on a faceplate.

Every source of this size seems to be very expensive wherever they come from. I would check out the backplate listings on ebay every day, you could be lucky.