Hands-free threading is a provocative claim, but my investigations suggest it's doable with no other electronics than a VFD, and at minimal cost, and the crucial enabling element is the swingup concept.
I'd have to say this is the single most game-changing idea I've come across since I first made a curly chip.
I feel a major debt of gratitude to those who took the trouble to share their discoveries, and make the brilliance of the idea so plainly evident. I wanted to repay that in some small way, and recognise this forum as a key incubator, and I thought the best way would simply be to try and keep that discovery and disclosure and discussion process going, in however small a measure, for the greater eventual benefit of the entire manual lathe-using community. I personally think the idea is good enough to spread virally, given the right initial conditions.
Like most people I've tried to interest in the idea (in conversation or by email), I was stuck on the notion of backlash in the leadscrew drivetrain being a potential problem.
Even once the early adopters here had reported, entirely convincingly, that it wasn't, I still wanted to understand why it wasn't.
The thought experiment which finally made this clear to me was to imagine the round workpiece 'unrolled' to a flat workpiece under a planer or shaper, with long pre-existing V grooves at a slight angle to the travel of the toolhead. This angle would correspond to the thread's helix angle.
It's pretty evident the clapper box (unless it's really stiff) would happily actuate if the feed were reversed. If necessary, the V tool could presumably even 'bump' its way over several grooves, if the travel corresponding to backlash being taken up in reverse was long enough.
This explained the observation on this forum that even if the lathe were slack enough to require several turns of the spindle (ie several grooves of the thread) to take up the lash, the tool would simply pass over several crests and troughs in succession.
For me the major barrier to understanding had been feeling in some rather vague way that the V tool flank will be pushing sideways against the thread flank during the backlash takeup period. This, I now realised, was an illusion caused by the operator sharing the frame of reference of the tool, and discounting the frame of reference of the rotating workpiece, perhaps because, unlike the tool, the silhouette of the workpiece is not 'going anywhere'.
In the planer analogy, it's clear that the work is almost pushing tangentially to, ie "in line with", the clapper rotation, with hardly any side component, so there is little friction to defeat the clapper clapping.
Anyway, I set about trying to come up with a way of incorporating the concept onto my (biggest) lathe, a slant-bed Willson, which would automate as much as possible of the single-point threading process.
Here's a couple of shots (if I can work out how to attach them) of the finished tool.
If there's any interest I'd be pleased to write up some of the learnings from building and using this, and outline how I set about making the operation hands-free for several passes at a time.
I can see there's potential for making it almost entirely hands-free, but I'm not sure there's much to be gained, except perhaps that it sounds good. However a degree of 'hands-free'ness is beneficial 'cos you can reapply cutting compound with one hand while the other works the speed control (it sometimes being beneficial to slow down at the ends of the auto reverse cycle)
