Old Singer Sewing Machine - No Variable Speed

On 4/22/2009 1:17 PM snipped-for-privacy@gmail.com spake thus:

That sounds like a real old-timey one.

They're just rheostats. If you're intent on fixing the one you have, rotsa ruck: that's a restoration job that may require materials (e.g., graphite discs) not easily available anymore. It sounds like there should be some intermediate contact points between the ends of the ceramic tube that make for variable resistance; see anything like that? Obviously, the ceramic, which is an insulator, isn't going to allow any such contact.

If you just wanted to get it working you could use a more modern foot control, which is also just a rheostat but usually using resistance wire instead of carbon objects.

Have you tried poking around the graphite pieces with an ohmmeter? You could see if maybe there's a break in continuity (electrical) somewhere that's making it go all-or-none.

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The contact resistance between the carbon discs is varied by the pressure on the stack (in a similar way to the action of a carbon microphone). There will be some sort of compression spring between the operating lever and the top of the stack (it might be a leaf spring). When the spring is almost fully compressed, a contact by-passes the resistance stack and gives full power.

It sounds as though the compression system isn't functioning or the by-pass contacts are closing too quickly. You need to identify an adjustment screw somewhere in the linkage to the compression spring and set up the pressure on the stack so that the compression is minimal when contact is first made with the stack and increases until the motor is nearly at full power before the by-pass contacts close.

I can supply a photograph of the inside of the controller for a 1950s Model 201K (for 150 to 250 volt operation) if that would help you.

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It may also be possible to simply buy a replacement foot-pedal rheostat but it would have to be matched up in terms of resistance range.

Of course, if you want authenticity, you'll have to repair it!

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Yep. Two types. Carbon pile and wire wound rheostat. Both act as a series resistance between the 117VAC and the motor. They both have a slider that moves back the forth along the pile or "coil" to vary the series resistance. You'll also find an identical control inside the foot pedal found in old pully driven dentist drill motors.

I was my fathers sewing machine mechanic when he was in the lingerie manufacturing biz.

Any particular model number Singer sewing machine? All their machines were not created equal.

Not a very useful article, unless you want to buy the book:

Methinks a new pedal is cheaper.

That's the carbon pile variety. Duz it look like this?

or this one?

Yep. It varies the resistance. I could probably measure the resistance of some of the dental drill foot pedals I have hanging around, but there's no guarantee that it's exactly the same as what Singer expects.

Forget the motor and drag out the ohms guesser. Unplug the power so that you don't become a statistic. Measure the resistance and make sure it's fairly proportional to the foot pedal depression. If it jumps abruptly at one point, look for a crack in the carbon pile.

Ummm... you might also try asking in one of the antique sewing machine collector forums.

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No one has said anything about replacing the pot with an SCR or triac controller.

Sacrilege! It's probably an antique Singer sewing machine. Trends towards modernization of antiques are highly discouraged by convention among collectors. The desecrations of cherished antiques never seems to end. The slippery slope of modernization and evil upgrading will soon lead to the total replacement of the entire sewing machine. Such things cannot be tolerated. Maintaining an old machine is an art. Doing the same to a modern plastic equivalent is often a waste of time. Best to restore the old Singer to its original condition than to butcher it into some manner of hybrid contrivance.

It's a marginal idea anyway. Small sewing machine motors use solid carbon brushes. That's fine for low duty cycle, variable speed, and minimal load motors. Add an electronic speed control and the brushes now see a higher frequency component in the wave form. The result is a slight increase in arcing of the brushes, which causes increased wear of the copper commutator sections. Modern brushes are a sandwich of graphite (for lubrication) and carbon (for conductivity) to prevent this type of wear. My guess(tm) is that an electronic speed control will take about 25% off the life of the motor.

Some instructions and clues on rebuilding sewing machine motors:

"The next step is to clean the armature commutator. This is where the carbon brushes make contact. 90% of motor's troubles comes from a bad commutator. Heat, oil, carbon accumulation and dirt are the ideal mix to provocate(sic) sparkling when electricity is applied to the motor. Under load, the sparkling will increase and some motors will start smoking..."

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Wow - nice to see there's still activity on this list, and thanks for all the replies!

KISS is my driver. I'd like to keep it simple, and cheap. Fixing the existing part (if possible) is nearly always my first choice. Besides, I no longer have access to my bench and most of my equipment - all I have here is an old Weller soldering iron, some solder, my favorite Tek scope, and a box full of parts I needed to fix something recently. All the rest is in storage :(

Anyway, here's a shot of the pedal's guts, with some labels to help clarify.

1. Spring and Linkage. This is pressed downward when the pedal is depressed.
2. Brass Linkage/Contact. This moves to the right via linkage 1 when the pedal is depressed.
3. Copper Contact. This moves to the right and toward the graphite contact on the left end of the Carbon Pile when the pedal is depressed.
4. Carbon Pile. This is a long ceramic tube filled with ~100 graphite discs and a graphite contact on either end.
5. Bypass Contact. When the pedal is fully depressed, the Brass Linkage touches this contact and bypasses the Carbon Pile.

Now - here's what I didn't mention previously... I got this thing in pieces at a garage sale, along with the sewing machine. The previous owner had dropped the pedal, cracking the bakelite and spilling its innards all over. He assured me nothing was missing, and when I fiddled with it, it all seemed to fit into place (as shown). BUT, I'm not 100% sure I'm not missing something, and I'm also not 100% sure I have it assembled correctly. The Copper Contact was as shown (nearly straight) when I got it - it doesn't make contact with the Carbon Pile until the Brass Linkage is nearly touching the Bypass Contact. Also, the slot where the Copper Contact and Brass Linkage tie together is held together very tenuously - I'm afraid it's going to fall apart every time I fully-depress the pedal.

So what I could use here is an evaluation of the parts and placements

- do I have everything? Is it all in the right place? I can't figure any other way to set it up. Any other thoughts?

Thanks all!

-Pete

On 4/23/2009 10:12 AM snipped-for-privacy@gmail.com spake thus:

Pretty clear how it works now; as someone described up-thread, the pile of carbon discs gets compressed, reducing their resistance. So obviously this happens when the spring on the left (3) pushes on the metal stud at the left end of the ceramic tube.

So apparently the problem is either that the carbon discs aren't making enough contact with each other inside the tube, or are contaminated, or that there's not enough pressure being exerted on the left end of the tube by that spring. Which could mean that either it's not put together correctly, that there's a part missing (though I can't see where), or that something needs bending or some other adjustment to work correctly.

--
Save the Planet
Kill Yourself

- motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/)

[...]

It looks as though you hve got everything in the right place

[...]

That's why you aren't getting a gradual start-up, the resistance isn't coming into play until too late in the operating sequence.

Gently curving the 'copper' (more likely phosphor bronze) strip towards the pile would cause it to make contact earlier and would also change the angle of the fork so that it held the brass linkage more positively. Perhaps the fork should be angled more sharply to make sure it is well hooked into the strip (be careful not to crease the metal and snap it).

Have you checked the carbon discs to make sure that some of them aren't shattered - or some might be missing?. That would make the pile too short to touch the 'copper' strip properly.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

I would try adding some (conducting) padding at the centre of the bronze spring (around the "3" area) to make contact with the carbon. Is it possible a copper/brass disc is missing around there?

--
Geo

Just fixed one of these and found this ancient thread. Thought I might put this up for people finding this thread. The carbon discs get burned, so go through the stack and discard any that have broken, then take a very fine s and paper (600 grit)and lightly sand both faces of each disc. Make up the s pace for any discards or accidentally broken while sanding discs with some small washers. It is important that the gap be filled with something strudy , not foil or steel wool. We don't want springinees to the stack. The discs are poor conductors and need to pushed very hard together to decrease the resistance, therefore increasing the motor speed. You don't want the little metal nub at the end of the tube that engages the arm to be mobile. Do not bend the leaf spring unless you think it has been changed, it's tension is set to not break the discs. Good luck.

Good on you.

I went to an open day with these people

they have a room , with expert retirees , repairing hand and powered sewing machines as well as all the carpentry and engineering tool repair/reconditioning

just noticed this resource on their site

Very interesting. I started with my mother's treadle machine, and I have a barely "portable" from about 1950, but I mostly use a White rotary that 35 years ago my girlfriend's roommate found on the sidewalk being thrown away in NYC and managed to squeeze into the back of her VW bug, even with the table. She was gay and said that I was the only guy she liked at all.

But I'm posting because, in my search for zig-zag, I came across a Singer that depended on vacuum to control the speed. The person who gave it to me had lost the foot pedal, but I could test it by putting a hose on the connector and sucking on it. The harder I sucked the faster it went!!! Eventually I found a used pedal that wasn't too much money.

I wonder if that uses the same carbon discs. I sort of doubt it, but to find out I'd have to take apart the machine, not just the pedal.

My wife has a 35 year old Singer with the same type of speed control. Hers developed the same problem several years ago and increasing the disc tensio n slightly fixed the problem. If yours is unserviceable how about an old ti me sewing machine store? We have a guy around here that's been in the vacuu m cleaner business since Columbus came over. He has a supply of old vacuums from day one. Perhaps you might be able to find someone like that who may have one of these just collecting dust. I would have to agree with Jeff abo ut not using a PWM type of speed control. For the same reason I never put o ne on my 1953 Lionel train set. Lenny