Sewing Machine Motor to Drive Watchmaker Lathe

[measuretwice]

1 hour ago, jdrichard said:

I thought the voltage stayed the same but the current was reduced in the windings. I am an EE but i hated machines

What Marc was referring to is PWM - pulse width modulation.  DC is on 100% of the time.  PWM powers a DC (or universal) motor by picking a frequency (say 1kHz) and then varying the % of a cycle that the power is on.   I don't think PWM has better torque properties than varying the voltage, but for sure its better when changing speeds, much smoother.  The cats meow is a encoder on the motor so the controller will vary PWM to maintain a constant speed - take a heavier cut, the controller senses things slowing down and gives it more juice to maintain speed.

Constant torque is great for say a conveyor belt where you only need X amount of torque regardless of speed, but on machine  tools, we very often want increased torque as the speed is reduced - i.e. constant power.  There is no electronic way (VFD, PWM etc) I know of to maintain constant power which is why mechanical transmissions are the best way to control speed.  Don't get me wrong, I have variable speed on most things for convenience, but also the pulleys and counter shafts do an excellent job of lowering speed and raising torque.   It may be a bit moot as so little power is needed on a watchmakers lathe, and you can lick the problem by over powering.  For example, a 1/4 or 1/2 hp at full RPM will still have lots of torque for watchmaking at 1/10 the speed..... however a much smaller 1/10 hp motor at 1/10 its speed at full DC (either by voltage drop or PWM) will only give you 1/100 hp. (rounded, ignoring losses and all other things being equal )

 

On 10/30/2017 at 6:12 PM, StuartBaker104 said:

I bought a new sewing machine motor specially for my lathe and it works perfectly. See here http://www.ebay.co.uk

 

Stuart, does the switch control speed, or just on/off....i'm guessing just on off?

 

Edited November 1, 2017 by measuretwice

[jdrichard]

Stuart, does the switch control speed, or just on/off....i'm guessing just on off?
 

So the power from a sewing machine motor is basic AC motor Magnet, stator and armature and a current draw on .9 Amps across a drop of 110 volts. The Foredom foot pedal i think is a VCM in a chip. It still has a hard time producing smooth power and makes the motor jittery when running. The old resistor based ceramic discs still have a very smooth transition in speed as in controls the P=IsqrdX R, where R is varied.


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[StuartBaker104]

20 hours ago, measuretwice said:

Stuart, does the switch control speed, or just on/off....i'm guessing just on off?

No, it has a foot pedal which gives a smooth control of speed from 0 to 7000 rpm. I don’t use a countershaft pulley system, just a single belt (long rubber o-ring) onto the lathe pulleys. I’ve never struggled for torque from the motor but have had the belt slip.

Sewing machine motors vary in power output. This one is 120W which is about 1/6HP, although I suspect the rating is the electrical input with only 75% of that converted to mechanical output. I’ve not dismantled the controller but it’s presumably just a rheostat.

 

[jdrichard]

No, it has a foot pedal which gives a smooth control of speed from 0 to 7000 rpm. I don’t use a countershaft pulley system, just a single belt (long rubber o-ring) onto the lathe pulleys. I’ve never struggled for torque from the motor but have had the belt slip.
Sewing machine motors vary in power output. This one is 120W which is about 1/6HP, although I suspect the rating is the electrical input with only 75% of that converted to mechanical output. I’ve not dismantled the controller but it’s presumably just a rheostat.
 

How many amps is your motor. (V x A)/746 = Horsepower


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[jdrichard]

Update. Drilled two holes is a L bracket lined up with the slots in the lathe base stand. Then i drilled one hole in the tom of the bracket for a nut and another lower for a turning handle and nut, for belt adjustment. See pics. Now i still need to make a belt for the large pulley. Plus i used washers and wing nuts for hand tightening.


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[StuartBaker104]

8 minutes ago, jdrichard said:

How many amps is your motor. (V x A)/746 = Horsepower

The rating plate says 0.5A, so 230*0.5/746 =0.15 HP,  which is pretty close to 1/6HP as convrted from 120 watts.

[StuartBaker104]

JDR’s motor above is 0.9A at 110V and therefore 0.13HP, or 90W if you prefer.

There will be more losses through the additional belts, but I'm sure this will work fine.

[jdrichard]

I have finished the assemble. I melted the green belt together and used a drumel tool with a sanding disk to smooth out the area where the belt is melted together. I have attached a video of it working. Not sure if the sewing machine motor is working too hard or not.

 

 

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[jdrichard]

I am now the proud owner of five sewing machine motors. I added the plugs and tested them all and they worked fine. The PCM of the SCR component on the Foredom and Lowboy pedals cause a bit more slight roughness than a analogue plain resistor type pedal, however, they will not damage the motor and work fine. Here are the last three motors


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[Ace864]

I also heard that the sewing machine might work on a lathe, but probably not each model is suitable. Lathe needs a more powerful motor, so you need to find the closest that can fit, and also modify it a bit.

[Ace864]

By the way, I can recommend you to try using an overlocker sewing machine. My friend used to take overlockers' spare parts, and after modifying them, placed them in other equipment. He did it with old unused machines instead of searching for spare parts. The overlocker motors are more powerful compared with the regular sewing machines, and their work speed is faster. Check here for more info http://sewingmachinebuffs.com/7-differences-between-sewing-machine-and-overlock-machine/. In case you won’t be able to find the required spare part, probably an overlocker machine’s motor will be more suitable.

Edited September 29, 2020 by Ace864

[marcoskaiser]

Interesting topic!

I just finished mounting the same setup, but was worried by the big jump in speed that a few millimetres of pedal action give, and the variation.  So I installed instead a variable knob to be operated by the left hand. 
other issue is the ratio between wheels. The 7000 rpm speed seems overkill. 
What is the maximum speed experienced turners use? 
 

(I obviously must learn how to weld a belt as well)

[jdrichard]

I also heard that the sewing machine might work on a lathe, but probably not each model is suitable. Lathe needs a more powerful motor, so you need to find the closest that can fit, and also modify it a bit.

Works well if you use a Countershaft


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[jdrichard]

Interesting topic!
I just finished mounting the same setup, but was worried by the big jump in speed that a few millimetres of pedal action give, and the variation.  So I installed instead a variable knob to be operated by the left hand. 
other issue is the ratio between wheels. The 7000 rpm speed seems overkill. 
What is the maximum speed experienced turners use? 
 
(I obviously must learn how to weld a belt as well)
http://d1v6dnm22vfd7d.cloudfront.net/monthly_2020_09/B49C671A-C18A-4F8C-950F-19AD09259E72.jpeg.547197aa8dde2da1810041958fc1dd28.jpeg

You should make a leather lathe belt and rid of those crappy plastic type belts. Here is the video I mans in doing this:

Making a Watchmakers Lathe Belt

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[jdrichard]

Making a Watchmakers Lathe Belt

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[nickelsilver]

Nothing wrong with leather belts but good quality round "rubber" works great if joined correctly. It's used all over the place industrially. I have belts that have seen many hundreds of hours of run time that show no sign of breaking or wear.

[transporter]

I use big O rings, I buy a couple at pennies each, fit both at the same time and have the one hanging loose just in case the other snaps halfway through a job, I can then slip the other on straight away. I’ve had one snap which came with my lathe. I had used it weekly for a couple of years before it gave out so I’m happy how long it lasted.

[luiazazrambo]

The Watchmaker's and Model Engineer's Lathe: A User's Manual by Donald De Carle

It says that 1/16 or 1/20  HP is enough for most general work and the max power you will ever need for clockwork is 1/4 HP which is about 185 Watt.

Edited June 15, 2022 by luiazazrambo