GH1440 Lathe Bed Conversion

[Valfar]

Hello,

New guy here and glad to be part of this forum.

I'm in possession of a GH1440 Lathe Bed + Headstock + Tailstock (a quite rigid base I would say) and I'm willing to convert it into a CNC lathe + 4th axis Router/Mill. Will be used for Al alloy, steel and perhaps some plastic, for hobby and prototyping (max 50mm O/D parts, but occasionally bigger O/D parts as well). Ideally, I'm willing to achieve 0.01mm tolerances.

I've got a lot of unanswered questions as you can imagine, but at the moment I cannot decide how to proceed with the lathe spindle, which will be the 4th axis as well. To make it simpler, I was thinking to design it to be able to mechanically switch between the lathe and the 4th axis mill. So the first question is what motor should I use for the 4th axis / lathe spindle? I was thinking to go for a high torque NEMA34 hybrid stepper (servo stepper) but I calculated it wouldn't give me much RPM for the lathe spindle (about 300RPM). How much RPM would I need anyway, given the parameters? Would I need 2 different motors instead, one dedicated for the 4th axis and another one dedicated for the lathe spindle?

Anybody who finds a free minute is more than welcome to suggest/advise anything.

Many thanks!