Lathe Build - Disengaging Motor From Lead Screw - HELP !

[Naboo]

Not far from a functioning lathe, but ran into some issues with the drive motors if anyone has some alternative ideas please ?
Bit of a head scratcher... Turns out I'm not great with physics

I am running one motor to get nice smooth running and precision, but it's speed range is very slow. so incorporated the cheap fast motor to handle the machine rewinds.
Originally I tried this setup and incorporated a one-way bearing on each motor, hoping it would allow the other motor to slip while one's running.. but have realized that's definitely not going to work.

Lead Screw Example.png

I have scratched my head for days and came up with a couple ideas, but they're over-complicated, and potentially very expensive, especially involving electromagnetic clutches.....

Average Ideas.. You Can Do Better.png

Does anyone have any ideas they could throw my way please ? or maybe some components I could look up that I may not have even heard of before ??
Have also thought about dog-clutches, and claw-clutches but am struggling to make this work

Cheers
B

[misjah]

just use 1 motor...you can also just disengage the carriage from the leadscrew and move by hand as on VMS70.

[dubcutter89]

I have made similair systems with just one motor - Not crazy fast but unless you have to cut 3 LPs per hour it's ok..
Good motor and good electronics needed. Not the cheapest, but as usual you get what you pay...

just disengage the carriage from the leadscrew and move by hand as on VMS70

Standard if you have a VMS32,62,66,70 or a lathe with a HALF nut, not useful advice if you have something without like a VMS80...

Lukas

[dubcutter89]

...or you clone Souri system by using a nut to engage the motor to the (hollow) leadscrew and a handcrank to move manually...

[misjah]

I have made similair systems with just one motor - Not crazy fast but unless you have to cut 3 LPs per hour it's ok..
Good motor and good electronics needed. Not the cheapest, but as usual you get what you pay...

just disengage the carriage from the leadscrew and move by hand as on VMS70

Standard if you have a VMS32,62,66,70 or a lathe with a HALF nut, not useful advice if you have something without like a VMS80...

Lukas

yes of course you need a halfnut...that goes without saying...i have both systems here.

[Naboo]

Unfortunately I don't have a half nut setup. It's an igus positioning table. And the main motor I'm using is the same as VR, so far too slow to use to drive it back to the start

I thought originally about the VR style hollow lead screw setup.. souri's a genius there.. but far too tricky to machine and couldn't find an existing hollow lead screw. Maybe a similar "nip up" kind of thing could be implemented by each motor

As is it will still work, I just want to avoid back driving each motor while the other runs. All the prototype electronics are done to get all the right speed ranges

[Naboo]

Agh, turns out most electromagnetic clutches don't actually mount the second shaft to the outside of the body.. only some.. which would require the slip ring etc !!

Found some tiny electro clutches with a 6mm internal, and a large gear or plate on the other end. with some small adapter shafts this will be nice and simple.
one switch on the motor controller can simultaneously flick a voltage from one clutch to the other


If anyone else is going some odd setups and needs these;

https://www.aliexpress.com/item/1005003278133098.html?spm=a2g0o.productlist.0.0.5c4176c8eluUug&algo_pvid=c9553899-c606-4251-8f2c-ad042f1d508f&algo_exp_id=c9553899-c606-4251-8f2c-ad042f1d508f-7&pdp_ext_f=%7B%22sku_id%22%3A%2212000024990489967%22%7D

[dmills]

What's the problem with a couple of spragg bearings?
You could drive the leadscrew via a flat belt and just have a lever and idler that introduces slack in one position, let it backdrive the high speed motor when cutting?
Same idea, but with two belts, two idlers and a pair of stacked pulleys each end of the belts, gives you a 'gear' lever that has a low and high speed position and lets you get away with the single motor.

I went for a servo motor driving thru a 50:1 strain wave gear, not horrible when the servo can wind up to a few thousand RPM at full shout, and you still get ~100um per turn at low speed in incremental positioning mode which works down to only a few rpm.
Yaskawa seem to make decent gear that has speed as a first class citizen (Some servo motor manufacturers have a bad habit of treating position as being the thing and not providing useful speed modes).

[Naboo]

I tried a spragg bearing on each motor, but as they're facing each other, the opposing motor still gets back-driven unfortunately

That sounds like a good idea also. I'm not very good with gearing and ratios though hahah..
Bit of an experiment, but will try these clutches. means all clutch and motor control is from a single desktop console that will sit beside the lathe


A local electronics wizard has made me some circuits that make the main motor run from 1-12 rpm for cutting, then with a push/hold button moves power onto another pot to set a leadout (Boost) speed on the same motor from 12-28 rpm. then another circuit running the other motor to rewind at around 200 rpm