Hacking an industrial sewing machine by adjusting the clutch motor

A few years ago, after my plastic portable machine broke, I bought a Singer 20u73, light industrial sewing machine. I was pretty tired of slow, weak machines with low torque. Going through 4 layers of fabric was a struggle so of course I went all out and got this nice machine.

[flickr 1907644244 ]

Unlike little portables which turn on the DC motor when the foot-lever is pressed, industrials use a clutch motor. The motor is running the moment you turn it on, and when the foot-lever is pressed, it moves the clutch towards the motor, engaging it. This means higher torque when you turn it on, thus getting rid of the frustrating “have to help the machine along” stuff necessary with small sewing machines. Great. only problem is that the motor runs at a perky 1750 RPM and the clutch is very sticky. This means it requires some practice to get used to the foot pedal: instead of being linearly related to stitch speed, its much more ‘exponential’. Seems like either nothing is happening or its going at a ridiculous 2000-2500 stitches a minute — much too fast for someone out of practice.

The solution? Basically everyone says “you’ll get used to it with lots of practice.” Which is another way of saying “this design really sucks”. (There’s DC servo motors that have no clutch because they can give high instantaneous torque but I’m not 100% sure they solve the speed-control issues)

Another solution is to change the pulley, which will bring the max speed down, and tweak the clutch setup for better response. For $20 it’s a nice simple fix. I spent a few days figuring out how the hell one does this. I figure if I post all of this now it will possibly save someone else the hassle.

p.s. You could screw this up and hurt yourself – 1/3 HP motors don’t stop for you or your hands. If you aren’t comfortable with this sort of mechanical assembly and disassembly, maybe have your sewing machine repairman do this for you?

Click “more” for the full article

[flickr 1907811366 ]

Step 1. Go to this website on pulleys and belts. Its the best thing ever. My motor is 1/3 HP and 1750 RPM. The center distance on my machine (the distance between the center of the pulley on the motor and the center of the pulley on the sewing head is about 16.5″. Pulley 1 (on the motor) is about 3.8″. Pulley 2 (on the hand wheel of the sewing machine) is 74mm according to the manual, which translates to 2.9″
Plug this in and press Calculate. Look for “R.P.M. Pulley 2″ which is basically stitches-per-minutes. On my machine it was 2200 spm. I’d like to crank this down a bunch. By getting a smaller pulley you can change the gear ratio to your favor. Change Pulley 1 from 3.8″ to 1.75” and press Calculate. Stitches-per-minute goes down to 1000, more than half the speed!

[flickr 1906984363 ]

Step 2. Buy a pulley. You can get a 1.75″ pitch diameter one at Sailrite. Basically make sure its a pulley for a motor with 3/4″ keyed shaft and a 3L size v-belt. Should be able $8-$10. I was lazy and spent more money for an adjustable pulley from mcmaster-carr (they didn’t have a fixed pulley in the right size). Having an adjustable pulley is probably not what you want but it is kinda neat. You can separate the plates of the pulley to get a different pitch.

[flickr 1907830572 ]

Anyways, if you get an adjustable one, just set it to max width, and tighten the set-screw. Make sure its not -too- wide that the v-belt binds. The two halves should be ‘flush’ with no threads showing on the outside or inside of the outer edge.

[flickr 1907834652 ]

Step 3. Remove old pulley. Take the guard off, remove the pulley and make sure you don’t lose the tiny metal key.

[flickr 1907815838 ]

Step 4. Install new pulley. I had to put this one backwards, but if you get a non-adjustable pulley like the one from Sailrite it should go on just like the old one, with the key to the right. Make sure the key is in. I had to file mine down just a bit to make it fit. My setup is not ideal (its less safe), but it works for illustrative purposes:

[flickr 1907839964 ]

Step 5. Get a new v-belt. Look on the pulley calculator page, under belt length it says “40.3” which is the ideal length. You can only get then in full-inch lengths so get the closest value. Say 40″ in this case. Note that you’ll have to measure your setup’s center-to-center length to get the right number here! Mcmaster has these too, they’re 3L sized fractional-HP v-belts, $5 each.

Step 6. You’ll probably have to adjust your motor to get good tension. The way to do this is to screw/unscrew the nuts on the long, vertical bolt shown in the center this photo:

[flickr 1907845344 ]

Move the motor up or down so that your new belt is well-tensioned. Not knowing the best way to verify this I guessed that the belt should be able to wiggle 1/2″ at the center when tensioned right. YMMV.

Once the tension is good you can adjust the rest of the clutch motor. First of all, make sure the belt has clearance, and move the motor on the mount to get this right. I doubt it’ll be a problem if you just get the non-adjustable pulley.

If you want max-control, put the foot-pedal bar on the left-most mounting hole. Adjust the length of the bar so that the pedal is pretty much at the angle you want to use it (you’ll adjust it again later).

Now adjust the 5/8″ bolt that is right in front of the pulley, it has a nut that you’ll have to loosen first. This bolt sets where the clutch sits. Basically you can use it to eliminate ‘deadspace’ in your pedal travel. I found that the ideal setup has it so that when then pedal is not pressed at all, its a bit hard to turn the hand wheel. This means the ‘brake’ is engaged. When you lightly press on the pedal it should release and you can turn it easily. This way you can use your heel to brake the machine. There’s also a wingnut to adjust the spring return of the clutch.

I don’t have a magical formula for adjusting these but basically mess around with the pedal-rod length, the clutch adjust bolt and the spring adjust bolt until you have a comfortable pedal angle (rod length), amount of travel (pedal rod mounting holes), break-release-engage capability (bolt) and its not too hard or two easy to press the pedal (wingnut). Do all of this with the machine unplugged, for crissakes.

When you’re done, make sure the pulley setscrew is tightened, the clutch bolt nut is screwed on all the way to prevent the bolt from vibrating loose and you have v-belt clearance. Put the pulley guard back on and power up your machine. Mine hums along at a nice pace and once I get better at dealing with the clutch I may move back to a large pulley. Have fun!

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  1. Even with a consumer level machine, I find the pedal’s sensitivity irritating. There should be a way to dial in what scale you want the pedal to run at. For that matter, at times (embroidery) I’d prefer to have a hand controilled dial I couuld just set the speed to.

  2. yeah, dc clutchless servo motors pretty much do this in an intelligent fashion.

    on ‘home sewing machines’ the pedal is just a rheostat, just a potentiometer with 2 pins connected. the harder you press it the lower the resistance and more power to the machine. hacking your pedal so that you could switch in and out extra resistance (use 1W-5W resistors of course) is probably all you need. Or maybe just wire up ANOTHER rheostat box next to your sewing machine in line with the pedal and then use that to set “max speed”

    you could also see its possible to change the pedal rheostat from exp to linear or if its linear, to log (inverse exp). Lots of fun stuff. of course you should not do this with an industrial as a resistor is not going to cut it when regulating a 1/3HP motor!

  3. I have a Husqvarna machine which gives essentially full power from a dead stop. Works great for sewing over that huge hump of a side seam when hemming blue jeans. The foot pedal feels nice and linear, and is fairly light. I’m guessing it is a control pot in the pedal with a solid-state servo’ed motor controller on the other end. Works like a charm and once the machine punches through and get some inertia going, it doesn’t rev up like crazy (unlike my old Singer home unit from the 60’s).

  4. ‘on ‘home sewing machines’ the pedal is just a rheostat, just a potentiometer with 2 pins connected. the harder you press it the lower the resistance and more power to the machine. hacking your pedal so that you could switch in and out extra resistance (use 1W-5W resistors of course) is probably all you need. Or maybe just wire up ANOTHER rheostat box next to your sewing machine in line with the pedal and then use that to set “max speed”’

    HarborFrieght.com has router speed controllers for $9.99, I have a pair that I use for similar situations out in the shop. It’s a rheostat in a box with on/off/on bypass switch and belt clip.

    Thanks for the hack, I’m a sewing impaired maker that has been thinking about buying a machine to stitch teepee/yurt covers.

  5. You could always replace the motor with a DC motor and controller. You’d probably have to rework the motor mount but you could set your motor speed to whatever you want. I use a similar setup cobbled together on my lathe so avoid having to change pulleys for speed control.

  6. Another trick taught to me by a Parachute Rigger was to place a nerf type ball under the foot pedal to provide some resistance which helps with control.

    The author mentioned a Servo motor, many of these come with an adjustment to control the speed. They aren’t too expensive either usually $100 to $150.

  7. you don’t need a servo motor or servo controller,
    servo implies controlled Position.

    You need a Speed controller.

    there are many on the market. google it.

    for 1/3 hp it should be pretty cheap to find one.

  8. A sticky motor is surely the sign of wear. Yes, you will get used to it is a catch-all, but it’s rather true. Within a week I was used to my machine and was able to have complete control of it including slow stitching and full-speed as well. If you are happy with the pulley/belt change, then that’s awesome.

    I also wanted to say that I have installed and tried a servo motor on my own industrial machines and I have to honestly say that they really suck. If you feel like you have no control with your clutch motor, then you’ll most likely hate the servo motors even more. They sound like they are falling apart all the time and there is no smooth start. I found myself re-installing my clutch motors after a frustrating evening of trying to sew with them, and then promptly sent them back to the warehouse.

    With all that said… this is a great tutorial.

  9. Well, this may be an ignorant comment, but what about a pulse width modulation controller? It’s a common solution for smaller motors and I was under the impression that it was also used for motors of this size and larger. All you need is a 555 IC with a 2K ohm variable resistor and a 1K ohm ceramic resistor with the trigger going to a solid state relay.

    It’s quite simple. Just look up 555 breadboard on YouTube and look in Google images as well. It’s a very simple beginners circuit and it’s mainly used for controlling motor speed or strobing lights.

    The 555 can’t directly control a motor of this size obviously, but it can be used to trigger a relay that can handle far more power than this motor. The whole thing costs less than ten dollars even with a very high voltage and high current relay and it can be done on a breadboard without soldering. In fact, the solid state relay is optional. You could use a regular relay if you don’t mind a clicking noise.

    This may be inappropriate though. In theory it would work, but some motors cannot practically be controlled in this manner.

  10. The easiest, and cheapest, way to get some sensitivity in the foot control is something that professional upholsterers taught me many years ago. A few thicknesses of foam under the pedal for resistance is plenty to do the trick, and costs around a dollar.

  11. (Unrelated to sewing…) If only more people read Norman’s book.

  12. richfiles (Richard)

    I work for a company called Motion Control Group that builds various types of motors and controllers. I work specifically with DC Brushless motors (often called DC servo motors). These are not to be confused with stepper motors, which are a purely position based motor While it’s true that they are often used for precise position controlled applications (using a digital motion controller and an encoder), the motors can often be used for simple torque or speed controlled applications. For a sewing machine, you would want a velocity based controller, Possibly with a tachometer input from the motor. This is the same setup ised in DC brushless lathe and mill conversions.

    Speed is VERY EASY to control with a quality brushless DC motor and a velocity amplifier. You will NOT need a motion controller (unless you want to be able to say, have it wait 3 seconds, run at an exact numericaly entered speed, stop after “X” number of stitches and stop with the needle in the up position-but that’s way overkill).

    Serioulsy, all you need is a brushless DC (servo) motor and an amplifier to drive it. An amplifier can typically be electrically tuned to adjust the linearity of the speed. I work on some rather high end brushless dc motors and amplifiers that can support my full weight against the motor shaft with no gearing, when the motor is at a dead stop! Smaller motors and amps are available and can provide you with easy speed control. We have one product line that’s fairly new that has a small motor with an amp built right into the end cap. The controls are simply, a pot to control speed, and one switch to enable or disable, and another switch to set direction. That’s it. While new prices can cost a bit, ebay often has good deals. I went to a local surplus store last year and found a brushless DC motor and amp, made by the very company I work for no less, that looked like it had never been installed, but the pair set me back only $50. I think that set new would have been 10 times that price.

    Surplus and ebay auctions can definitely be the hobbyist’s friend. Just research… Know what you need before you spend money. Most manufacturers now a days have thier manuals online. If you see a brushless motor and and amplifier or controller on ebay, or at a surplus store, you can usually look it up on their website for free. In the example with the surplus store, I pointed out where they could find the manual. They printed out copies and included them with the motors and drives. They sold out in no time. Makes it much easier for hobyists and do it yourselfers when there are manuals. Get aquainted with the technology and the requirments of your application. It’s quite wasteful to run a motor constantly just to clutch it into opperation. I think that’s another reason brushless DC motor have gained such a popularity in the industry. No complex mechanical clutches, a wide range of fully electrical control options (everything from preset speeds, to analog pot controlled speed, to full out digital computer control), and the reliability of having no brushes to wear out, have all contributed to the use of thse types of motors.

    I myself am hoping to build an electric scooter using a brushless motor in order to eliminate some of the noise associated with the cheap electric scooters on the market today. I also plan on retrofitting brushless motors to my lathe and mill.

    In regards to the guy who suggests PWM. That is possible when done right, but a relay is absolutely not feasible. When switching a motor of that size, you’ll burn up your relay’s contacts in no time. You should be switching using at best a FET, or at worst, a transistor. FETs are the industry standard these days, and can switch motors at 20000 plus hertz on a high end drive. Most cheap brushless DC drives use PWM, but a few high end ones actually output a Simusoidal (sine wave) output that perfectly matches the motor’s position. Sine drives are expensive. PWM are fine for your application. They can be had cheap too.

    Most of the products made by my company are beyond the price range of most hobbyists and do it yourselfers, but the used, surplus and ebay markets are filled with options.

    Good Luck!


  13. question for chris thorp: what model is your Husqvarna?

  14. I have two industrial sewing machines. My Juki 5550 came with a DC servo motor. It is a dream. Totally quiet except when running, and then almost totally quiet. Smooth as glass. Speed control is smooth from a slow crawl to blazing fast with total control. My Pfaff 345 walking foot machine had a clutch motor, but I changed it to this one: http://www.allbrands.com/products/abp10568.html plus I bought the $10 extra-small pulley. It is super smooth, quiet and easily controlled from very slow to semi fast. I found the servo DC motors much easier to control than any clutch motor. And it fits the same holes in the table that the clutch motor used.

  15. It seems to me that some sort of motor controller with a feedback loop for speed control is essential, no matter what kind of motor is used.

    Also, I have to second Necoro’s recommendation of Mr. Norman’s book. I read that book a few years ago and enjoyed it a lot.
    It isn’t sewing related, per se, but it does certainly have a bearing on the design of a good user interface for the sewing machine.

  16. I have an industrial Singer from 1913. It too uses a clutch motor although the clutch and motor are separate pieces and there are no belt guards. I have to say it was a challenge at first controlling the machine, but it does get easier with practice. There is nothing wrong with the basic design. They have sold millions of these machines.

    Putting a smaller pulley on is a perfectly good idea if you want to slow things down. It is a gas to kick it into full speed on occasion but I do like the foam idea since the pedal is touchy.

  17. Along with what DIY Tactical said, you can also string a piece of shock cord from one stand upright, to the treadle and over to the other upright. This acts like a giant return spring and gives you mush better pedal control. Same basic principle as the nerf ball/ foam rubber but with adjustable tension.

  18. I bought an old singer 241-11 to repair some sails and make a bimini top for the sailboat. this article is just what i was looking for. my problem is i have a 3450 rpm motor and need to reduce to a 1750 rpm one so i have feed control for the heavy stuff. so i plan to buy an ac clutch motor but one supplier says this is not recomended for single needle machines with 3450rpm motors. why not/ i have to do something because i have no control when motor runs, its just too fast.

  19. HMX-1/MV-22 Osprey test team in Pax River had a machine just like this one. It was a really nice machine for small work. You use a machine like this, and you will never go to plastic. I’d go with what Duane said, but when I was in, we just used our hands on the pulley as a brake. Crazy, but we did it and did that often. Regards.

  20. Carl.. you can absolutely change out your clutch motor to the 1750 rpm model.
    I would like to add some comments on the mechanical adjustment of a standard clutch sewing machine motor. Please make sure that the belt tension is not too tight since this will cause the clutch arm to stick. The belt tension is adjusted using the two nuts on the vertical threaded rod at the front of the motor. You should have about 1/2″ play in the belt when adjusted correctly. The clutch arm has to move freely. Any mechanical binds in the tredle bar, tredle or the clutch arm itself can also cause control problems. Sometimes lubricating the area where the clutch arm pivots will help. The spring located under the tredle arm with the adjusting nut at the end is for controlling the return pressure on the clutch. After checking to make sure the belt tension is not causing a bind, adjust the return spring pressure as light as possible while still maintaining its ability to return the clutch arm to the highest position when the pedal is released. You should make these adjustments with the motor off. Check for binds by pushing on the tredle or pulling the clutch arm down with your hand and then releasing it.

  21. A little off the subject…Does anyone have any experience with soldering a motherboard for a computer machine? I have a Husqvarna 980 (over 25 years old) which I love. It has stopped working because an
    electrical connection on the motherboard has broken. I want to solder it back but I have never tried such a thing. The Husqvarna dealer says that it is not worth fixing, but I really love the machine. Any suggestions?

  22. evelyn: im sure its fixable, why dont you post to the http://forums.ladyada.net forums and ill take a look there? (its too difficult to do in post comments 🙂 )

  23. Hello. I have tried several of the servo motors that are on the market for industrial machines. The only one that has good control and power a low speeds is the reliable model mentioned above by DuaneB. also changing the drive pulley size will not help much. If you want to do this with pulleys you will need two more pulleys and another belt. You then can fashion a speed reducer. At one time these contraptions were available for purchase from industrial machine suppliers. good luk

  24. I have an “at home” sewing machine and do a lot of craft type sewing, including light upholstry work. My machine is not equiped to handle heavier fabric so I am interested in buying an industrial machine and am looking at the Juki du 1181. One site offered it with either the “standard clutch” or the DC servo motor – why do I want one over the other?????? From what I’ve read, I’m thinking the servo is what I want. Thanks for any information!!

  25. Unicorn Leather Saddlery-Traditional Hand made English Saddlery
    Great thread, I have learnt a few tips about speed control too!
    Doing most of my leatherwork by hand and having a old treadle 1930’s Singer 45k for 1/2″ leather as a back up now and again and various industrial and domestic singers without power for materials like cottons and nylons I upgraded to a new Industrial Yamata PF5318 RRP £1100.00 (you can get them on ebay new for £279.95 GREAT price and very good afterservice and guarantees) to bring me in to the real world as my machines couldn’t cope with new equestrian items I have designed and made. They were going in to clinical shock from all the work I was trying to give them.
    Having not used an industrial electric machine for at least 11 years it was a bit of a shock, as others have said, it’s full power or nothing(0 stitches to 2500 in less than one second-wish my motorbike could start as fast as that!) but I do think it’s my clutch control and not the machine and will shove foam under the footplate as others have suggested to give it some resistance.Given practice of about a month I am sure I can beat it, thanks to you all for ideas and suggestions.
    Caterham on the Hill

  26. Found this page last night. I was tearing my hair out, making a mess of a storm jib. Breaking threads, speeding and stopped, wiggley stitching. Had to do something. 3/4 horse slipping clutch motor has a huge pulley. Can’t get a smaller one tonight – no children, no dogs, so no squishey ball to put under the foot peddle. Aah! Shockcord! Got some! So I’ve rigged up the springy shockcord as suggested by Diz (thank you so much), and slacked the belt a bit (thank you Jim) did a load of lubricating, adjusted timings…Sail is finished now, just a little smaller where I got rid of the evidence. It worked for me.

    Bless the web.


  27. Hello everyone,
    I’m so greatful to find this site but still comfused. I have juki ddl 888, 3450 rpm, 1/2 H.P., industrial sewing machine. I too have speed controll problem to sew simple dresses. Is there ways to avoid having to change smaller pully or changing cluch motor by only i adjust knots & bolts in the machine? S.O.S. BEFORE THE SEWING MACHINE REPAIR MAN COMES

  28. We got Servo Motor from Keystone Sewing. It is excellent one better than our junk servo motor from ebay. Check at http://www.keysew.com/

    Stay away from cheap servo motor: See picture

  29. Hi I have a slight problem! I have a sunstar from Needles eye it is similar to the one on e the pic up top justlonger gap to swing heavy stuff around.anyway My needle broke and the shaft of the needle is up the bolt hole(convenient hey?)it broke at the top so its kinda stuck up there. I took the end of the head off and I can see where to undo a shaft but it won’t let me do it – apart from maybe using a strong magnet to pull it out, I’m not sure what to do next. I’m not good at mechanical stuff but it looks so obvious but it wont let me undo it.I live in a coastal toen so we don’t have a sewing machine guy anywhere. I’m thoroughly pissed at this as it broke on a cheap crappy horse rug I was fixing for someone I didn’t even know(I nearly chucked the thing out instead!) Hows that for karma Jocelyn

  30. Hi, I have a Bernina industrial sewing machine with a clutch motor. The timing was off on it and I just had it in for service. The dealer just wanted the machine, not the motor. They supposedly repaired it and tested it with their store motor. Today I tried it out for the first time and it still has problems. They tested it and said it was fine – stitch sample to show for it. Could the problem be my clutch motor?

  31. Thanks so much! I’ve installed a smaller pulley but I did not know about the bolts adjusting clutch travel. Thank you!

  32. I tried the shockcord idea and the ball idea on separate machines, a 491 Singer and a 260 Pfaff. Both ideas worked a treat!!! With the shockcord on the Singer I got down to 22 stitches per minute, which is far slower than my home machines. Thanks for the info.

  33. I’ve been looking all over for info on how to adjust the clutch motor. Thank you for taking the time to do this and post it for us.

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