Thread: automatic lead screw disengage

Hey, thats not a bad idea!

I have now used it in anger and have to say it works a treat.
I had to screw cut a thread into an under cut up against a shoulder,
I was quite nervous but the half nuts dropped out right on cue every time.
Normally I would have screw cut the thread in back gear to give me heaps of time,
but with this set up no problems at normal turning speed.
It's also easy to adjust the drop out point using the compound slide.

Nick.

PS I think Fred Hercus would have been well pleased

Good thinking.

Never thought of doing it like that. I can see myself making something similar.

It's going to take a bit of guts to let it do its thing the first few times though

Well done.

VERY novel way of disengaging, I must say!

I have been thinking of something along similar lines, but not as novel as your method, kudos to you!

The one thing that has stopped me, is not long ago, I replaced my half-nuts, got a set from Hercus here in Adelaide, and wondered, how did they ever get so worn out...

With your system, I understand that there is always going to be a passage, where the half-nuts are either fully engaged, and not, and this small area of partial engagement worries me, as the tool, and carriage are still under cutting pressure, yet the half nuts are only partially engaged for that brief period of time, which makes me wonder, if you would be accelerating the wear on the half-nuts.

I was thinking of something, whereby maybe a trigger - sear arrangement could be utilised, making the disengagement an instant affair. Problem is, that is only a half way work around, as I still wanted my cross slide to retract as well.

Anything electrical, would still be fraught with peril, as there is the hysteresis factor, depending on speeds, loads, etc... I discounted it as too hit and miss.

Mechanical is the way to go, but I think I've been looking at the wrong parts... lead screw, carriage, half nuts, etc. I still think, because my Hercus is belt driven, and the belt tensioning lever is in reach above the lathe, that maybe I should experiment with that. I am sure I could machine something, that either slowly, or quickly, allows the belts to slip, and maybe, on the unpowered side of the drive train, puts a brake on the belt, so the job stops at the same point. Then withdraw the cross slide, reverse the motor, re-engage the belt clutch, and repeat, without ever having to disengage the half nuts.

Just some ideas at this stage, there are also some viscous clutch pulleys out there, which can be electronically controlled, which would mean I could ramp down the contact - drag speed near the end of the cut as well, whilst leaving the motor alone.

Just my two cents worth!

Cheers


Ian