Threading on a Boxford TCL lathe

Spindle revs is increasing by one at each rev, and increases continually when running.
Spindle at speed stays false and and spindle index stays at false .
I cant get the true speed to match the speed called for because they stay in ratio so I would seem to need to alter the ratio to bring the two into line .

And Yes G21 is active

Looks like I have got there . a bit of trial and error to find a suitable figure


the pwm scale figure was 4627. Trial and error got me to 1100, the spindle at speed in hal meter fell true and all began to happen.
Somehow i suspect that I will have to change this figure for every belt ratio though.

I suspect I will use only two belt positions ,
One for speeds up to say 2500revs , and one low speed option like a back gear , ( I doubt if my motor will reliably produce enough torque at low speed, so I will probably have to manually change belt position along with a tool change for threading. Then suppose I can add a simple switch to say I am in back gear mode to prompt the software selection.

The lathe does not have a back gear , only belts,, but I do find that for most turning operations one belt ratio, along with the Sprint electronic drive unit (which varies the spindle speed quite effectively under pwm control) covers the speeds needed for most turning operations.
A change of belt ratio only therefore becomes necessary for high torque demands like threading.
The TCL is not a sophisticated machine . It is by definition a Training school lathe , and I see it my introduction to lathe CNC. As such it is unlikely to be producing complicated components.
It is probable therefore that I will only need two ratios .

I am guessing therefore that a much simpler piece of code to that outlined in the thread above would suffice for me. My problem is that with my current experience , that piece of code is beyond my capability..

Is it possible that such automatic speed detection will be added to linuxCNC?

Meanwhile I may try to find a single belt ratio which covers my current needs yet still provides enough torque at low speeds to permit threading with lighter cuts . (along with of course a suitable pwmgen scale number)

Thanks for your assistance on this problem so far.

Hi Andy and thanks
I have chosen a ratio which gives me speeds of 50 to 2000 rpm and I have found a pwmgen . scale figure which suits this, and gives me pretty close control in the low end of this range . It is nearly spot on at around 300 - 400 revs and does not impede the threading cycle ,
This gets me going for now (until the next snag comes along)
I will bookmark this thread so I can come back the the above links .
Thanks again