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I have recently acquired a Lorch LL instrument maker's lathe for which I need to source a motor.  I am planning on using a 3 Phase motor so that I can use a VFD inverter and hence be able to control the motor speed.

https://drive.google.com/file/d/1yoLJcPEZeQh8ueS-70Qw4jPmdtadtdf4EA/view?usp=sharing

My question is, what size of motor do people typically use on these small lathes?  It is a little bigger than a watch makers lathe with 65mm centre height.  It uses 10mm collets.  The lathe will be used in a clock repair workshop.

Thanks

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Sewing machine motors are popular. You could rig up a Unimat 3 motor. I used that lathe for Clockwork. It will take all long case clock wheels including the barrels and the motor will not idle. These motors are about on ebay.

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Thanks that helps.  I've looked at Unimat 3 motors and they are rated at about 100 Watts.

I was looking at the spec of a 4pole 3phase motor of a  similar rating and with a speed controller I'd be able to get between 130 and 2000 rpm.  Does that feel correct?

 

The alternative is a 2pole motor but the speed range would be between 300 and 4000 rpm which feels too fast.

Edited by mbhorology

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   a sewing machine will be too small (un less it is a leather sewing machine).  it looks like the pulley is made  for  a "round leather belt"?  I  would buy a variable speed motor with more horse power,  - better to control "belt slippage".  vin

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that is a very nice lathe, congrats.

I just looked at several watch makers lathe motors, they are all around 1/10 - 1/8 hp (say 75-100 watts) and speeds range from 6000 - 10,000.  Looking at the size of the pulleys they are likely a 3:1 reduction to the spindle.  There are Chinese made sewing machine motor for $30 but I agree 100 real or hopeful watts is not enough for that lathe.

A key thing with electronic speed control ( by a VFD or DC PWM) is that it might be constant torque, but that means HP drops as the speed drops.  If the motor is 1/4 HP at 3000 rpm, and you slow it down to 300 rpm electronically, you end up with 1/40 of a HP!   Constant torque is  great with say conveyors;  with a machine tool you ideally want constant power - speed goes down, torque goes up.   This is why mechanical speed reduction is always superior in everyway….but cost lol.  The ideal is a 3P w/ VFD or DC motor and use the OEM belt speed reduction.  I've a couple of Schaublin 70 and that’s what I did, best of both worlds - variable speed and full hp available

If you get the oringal stepped pulley on the motor all the better.   Nevertheless, if you want get electronic speed reduction, the idea is you put a much larger motor on it so it'll still have umph at low speeds.

VFD 3P is an excellent way to go.  A really cost competitive alternative is the 3/4hp Consew motor which I think is excellent (they are all over ebay/amazon).  It’s fairly cheap, just over $100 US, and is a DC servo drive that max's at 4500 rpm.  Given the pulley dia it seemed ideal to spin a small lathe at 4000 or 5000 rpm down to a few hundred.  As a servo, the controller gives it more amps if the servo feedback shows its slowing down - it keeps the same rpm with a varying load.    Some might think 3/4hp is too much buts not given you're using it for speed control, i.e low rpms it will deliver a fraction of 3/4 hp but still enough to do work on a little lathe.

I've an extra unimat 3 that I'm readying for departure and it didn't have a motor.  I put a Consew 1000 on it and am really pleased, so much so I've bought a second for my U3.  That lathe was underpowered imo but not any more, irrc it was 1/10 of a hp. 

The Consew motor is intended for an under bench mount for an industrial sewing machine and has a lever to connect to a treadle for speed on/off.   That I think is really important for watchmakers lathes, I currently use a miltifix but I dislike not having foot control and am thinking of getting a Consew and mounting it under the bench to drive watch makers lathes.  For larger lathes like yours or the U3, mostly used with a slide rest (instead of a graver), I think  speed control knob preferred.  Fortunately its an easy mod to convert the lever speed control into a knob control.  The black knob shown I added; its speed control and the lever just sits there disconnected.

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Edited by measuretwice

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