Saturday, 14 November 2020

Bantam CNC - sequence of events

 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:

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. At this point, the old leadscrew can be chopped down and the new ballscrew, ballnut, yoke, thrust bearing and pulley fitted.
  6. 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....

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Bantam CNC - sequence of events

 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...