To avoid tool crashing it helps to have an undercut at the end of the thread. I wonder if the leadscrews been changed. What lathe is it?
Is the 60 meshing with the tumble reverse?
I'm embarrassed to say that it was the other end I ran into (the tailstock end)! Must have been too ambitious in how much I turned in the top slideYes a runout groove is a good idea. Without one you stand a very good chance of digging the tool in at the end of the cut.
Would have thought so yes. Can you show a pic of the rest of the plate and the change gear set up? Is there a lever to select power feed or screwcutting on it?It's a Colchester Master 6" (probably 1930s).
Ummmm.... dunno - when I had the other set of gears on the tumbler was definitely engaged cos it was in the wrong direction initially. But that's worth checking, yes.
And my next dumb question is: Should it mesh with the tumble reverse?
Got 15 minutes in the garage tonight so had another shot.
Seemed to go much better (before I crashed the tool into the end of the piece!):
View attachment 231541
Today's problem (which was actually Sunday's problem, too!) is that the gearing / pitch seems way off. I'm going by the gear combos stamped onto the gear housing, and they are either out by around 40% or I am, once again, doing it wrong.
That thread above is supposed to be 4.0mm but seems to be closer to 2.5mm. When I was playing on Sunday I had it geared for an alleged 1.5mm but it was much finer than that.
This is the appropriate part from the table on the cover:
View attachment 231543
I put the 60 tooth on the main drive out of the gearbox, 50 on the banjo, and 63 on the leadscrew - that's correct, huh?
Plate above. I'll need to head into the garage tomorrow and get the rest of the pics - there is a single lever that powers the top slide, carriage or nothing depending how it's set.Would have thought so yes. Can you show a pic of the rest of the plate and the change gear set up? Is there a lever to select power feed or screwcutting on it?
Groovy - will measre the screw's tpi tomorrow, tooWhoops! Yes you gotta go easy on the infeed when threading.
Your machine plate suggests it has a 6tpi screw. If it does, then a 60 on the stud gear and a 63 on the screw gear should yield 4mm pitch (or near as dammit). If it has for instance a 8tpi screw you'll need to re-figure the gears.
Plate above. I'll need to head into the garage tomorrow and get the rest of the pics - there is a single lever that powers the top slide, carriage or nothing depending how it's set.
I'm embarrassed to say that it was the other end I ran into (the tailstock end)! Must have been too ambitious in how much I turned in the top slide
Same problem as another poster a few days ago. That's for surfacing and facing, not thread cutting.
It would certainly explain the too-fine 'thread' and the tool crash.
Scotl - the drop-out lever is for turning only. It basically engages a power feed to the handwheel to drive the carriage along by the rack and pinion. You have to leave it disengaged and use the other lever (the half-nut lever) to engage the half nuts on the leadscrew for cutting threads. The leadscrew is more accurate and repeatable for making multiple passes for cutting threads.
Since you're cutting a metric thread, you have to stop the motor and back it up to wind the tool back to the start without releasing the half-nuts.
Oh look... a single handle for sliding and surfacing. What a plank...
View attachment 231634
So my guess, being 25ft away from the garage, is that the circled chappie is the half nut engaginator...
The thread-dial-indicator is just to the left of it, so that makes sense.
Oh look... a single handle for sliding and surfacing. What a plank...
View attachment 231634
So my guess, being 25ft away from the garage, is that the circled chappie is the half nut engaginator...
The thread-dial-indicator is just to the left of it, so that makes sense.
- Don't do what I did when I started out and reverse the motor without retracting the tool thinking it would follow the cut back to the start - it won't, it just trashes the work by chewing up all the bits you don't want cut. Always retract the tool.