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David Nebenzahl

On 4/22/2009 1:17 PM spake thus:

Anyone know how these old singer foot pedals work? There's not much
to this thing, but I can't for the life of me figure out how it's
supposed to work!

The one I have contains a long ceramic tube filled with a stack or
maybe 100 graphite disks. One end connects to the sewing machine
motor (I assume), and at the other end there's a contact that's
brought closer to and eventually touching the contact on the end of
the tube as the foot pedal is depressed.

The foot pedal was dropped and I'm trying to repair it, but so far I
can't get any variable speed out of it - I get either off (when the
contact isn't touching the end of the graphite-disc-tube) or ON-HIGH
when the contact touches the end of the graphite-disc-tube.

Sorry for the miserable description - it's been about a month since I
had the thing apart - just figured I'd post here to see if anyone had
any suggestions.

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.

--
Save the Planet
Kill Yourself

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

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