Posted by Vic on 01/05/2023 12:53:51:
The MW lathe uses a fairly standard 72mm register and my WT chucks are threaded M33 x 3.5mm.
Please could you clarify the 72mm part.
Is that the spindle register?
If so, that seems quite large for a 14" lathe.
Is the lathe one that has, in effect, the chuck backplate integral with the spindle?
Reading JasonB's post above, I guess that it is so I think what you are looking for would resemble a backplate-mounted ER collet chuck, without the nut and having an M33 thread on it instead of the ER thread.
It may be that a standard backplate-mounted ER chuck could be modified (ER32 has M40 thread, but the wall might be too thin).
An alternative might be an ER20 one (M25 threads) and a bush which is M25 female to M33 male.
Edit:
One of these would work with the idea above:
https://www.ockenden-timber.co.uk/woodturning-chucks-accessories-nexus3r-woodturning-chuck-c-107_108_109_975/thread-adapter-insert-34-x-16tpi-to-m33-x-35-p-2908
just thread the inside to suit the ER thread.
The other option with that one is to surround it with what is effectively a thick washer so that its diameter matches the mounting holes in your backplate and then secure the two parts together (welding is easiest, any mechanical fixing has to resist axial and rotational forces).
Edited By DC31k on 01/05/2023 17:15:25