Jump to content

Sewing Machine Motor to Drive Watchmaker Lathe


Recommended Posts

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 by measuretwice
Link to comment
Share on other sites

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.


Sent from my iPhone using Tapatalk Pro
Link to comment
Share on other sites

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.

 

  • Like 2
Link to comment
Share on other sites

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


Sent from my iPhone using Tapatalk Pro
Link to comment
Share on other sites

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.3c5c5d67bf23a6b90e0eceb1195e2a67.jpgc472f97f9f117de9ec758aec7fb694a5.jpg


Sent from my iPhone using Tapatalk Pro

Link to comment
Share on other sites

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.dc029d0ccdd8fc3b52993b2493f8b830.jpg&key=657679a54a8e9b5ce3be9ec9c93ae785960dae218f220184c1804b00d307417258460876e5e3ac61fcd714848871c19b.jpg&key=2304435ea8a5fa77774a9318c3dfe58e768c9eedd771f343b9f999e2e786d4b9c71813d87dce8a7fab30ecf6323868c8.jpg&key=224331507582697e020dc6e6c4463657f8e2c2607bfb58f6d30f8b2d18d141b5

 

 

Sent from my iPhone using Tapatalk Pro

 

Link to comment
Share on other sites

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 48d2b8ba3fe99753749f4ff80939e57c.jpg


Sent from my iPhone using Tapatalk Pro

Link to comment
Share on other sites

  • 2 years later...

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 by Ace864
Link to comment
Share on other sites

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)

B49C671A-C18A-4F8C-950F-19AD09259E72.jpeg

Link to comment
Share on other sites

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



Sent from my iPhone using Tapatalk Pro
  • Like 1
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

  • 1 year later...

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.

lathe_mot.thumb.jpg.9d5ffefe998ed6d191a11a803e643561.jpg

Edited by luiazazrambo
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.



  • Recently Browsing

    • No registered users viewing this page.
  • Topics

  • Posts

    • As you are looking for a solution, keep in mind that you can order (or salvage from old crowns) male split stems with different length shoulders - the cylindrical section between the threads and the split coupling. The shortest are less than a millimeter, which gives you another variable to exploit since that would seem to be shorter than what you have in the picture. In their repair kit Benrus sold male split stems in Tap 8 or 10, with shoulders from 0.33-0.085 inches.
    • Nicely done. Looks good. Be cheaper than a bought one. More satisfying as well.
    • Yes well the 6497 spec sheet did mention epilam but I don’t have either the product or the bottle for it.   
    • Hello from Nashville TN!!! I’m new to the watch repair world, but I’m nerdy and loving it! I’m helping a friend out and repairing his old Benrus Square Rigger. Basically the crown was damaged (the internal pipe was bent badly…I tried to straighten it and it broke.) Anyways, I’ve learned a lot about this watch but I need some help  it’s a split stem system and I was able to source the correct stem. What I know so far. It’s a split stem, male side screws into the crown. 5mm crown. Tap 9. 2mm tube on the case. I bought a random lot of vintage crowns and was able to make one of them work. It’s the crown on the left side in the pic. The problem is, I need a gold one! I need to find a crown with a recessed “pipe.” The gold one on the right, that has a flush pipe will not work…regardless of how much you trim the stem. It’s has to be recessed like the steel one. I’m just not sure how to search for that!
    • Yes, it's a problem if you're not familiar with them as a 3rd tier brand with 90% of the cases being monoblock, especially if you get one of their chromed cases with faux joints like you ran across. The Benrus and Belforte watches (1st and 2nd tier) more often than not had some opening instructions stamped on the front loading case.  It is easier to tell when you get one of the Sovereign anodized aluminum one-piece cases, especially in Hot Wheels purple!
×
×
  • Create New...