There's a right way to do this:
Some of the critical machining work will need to be done on the lathe itself - stuff like modifying the existing X axis (cross slide) leadscrew and perhaps machining up the housings for the ballnut and thrust bearing for the cross slide. It's a question of "physician heal thyself", something that can't be done while said physician is out of action.
What to do first? Seems to me I should get the cross slide assembly done first, then move on to the saddle. Rather like doing the Z axis on the Bridgeport conversion before the more straightforward X and Y drives, as that's where the tricky stuff lay.
Sequence of events:
- Clean up the cross slide and saddle bodies and machine the cavities for the encoder scale, limit switches etc. Ideally but not necessarily including the ballnut yoke fixing holes, if I can finalise them in time. This will be done on the mill.
- Reassemble the lathe (apron, cross slide, power feed shaft etc), so I have a functioning machine again. Obviously I will need to mount the modified motor and recommission the VFD at this point.
- Machine up the cross slide thrust/drive housing and the cross slide ballnut yoke. These will likely require boring in the lathe but otherwise is mostly milling.
- Bore out the Rotex coupling for the cross slide ballscrew drive and the driven pulley, then machine up the cross slide ballscrew. This needs to be done on the lathe.
- At this point, the old leadscrew can be chopped down and the new ballscrew, ballnut, yoke, thrust bearing and pulley fitted.
- The drive servo could be fitted at this stage, although it would mainly serve to show it assembles correctly.
If this goes well, I should have a functional manual lathe with a ballscrew cross slide (X axis) and a servo drive. I can then move to the more straightforward saddle drive (Z axis), glass encoder scale etc.
So first, before I can proceed much further, I need to make my mind up about the saddle and cross slide mods I will finally go for. Although I'm not shy when it comes to machining the original parts, I'd rather not end up making a pig's ear of it.
The cross slide itself is fairly simple - machine a shallow slot on the hidden underside of the body to receive the magnetic trip. Then drill and counterbore the fixing holes for the ballnut yoke. I may do that later, as removing the cross slide is fairly easy.
The saddle is a bit more involved. Requires cleaning up the rough cast leadscrew cavity and making some slots for the encoder body and the limit switches. Let's get those features finalised next....