Sewing Machine Problem

We have a problem. Our problem is this:

Singer Model 347

This is a Singer Model 347, built in the sixties (it looks like) and it seems to be a sewing machine that can do what we need. However, it has exactly three speeds:

  1. Off
  2. ON!
  3. Manual

The ON! is the problem, in the sense that there are times when you don’t want the sewing machine to go full blast through your project; sometimes delicacy and slowness is required.

Here is the root of the problem:

Singer Model 347 Foot Switch

You can see in the image, to the right, the switch which is actuated by the foot pedal itself. This pulls the contacts from the left to the right, bridging the gap and completing the circuit. Here’s a pic with some annotations.

Annotated Foot Switch

I do not see how, if no parts are missing, this switch was ever intended as a graduated speed foot switch for a sewing machine. There are only two cables. I’m assuming one is hot and one is return and therefore this translates to an on, off switch writ large. Where the gap is bridged and the copper contacts touch, there’s no room for “play” in the touching or not of the contacts. I screwed around with this by hand and while, yes, there was a tiny bit of speed control just at the interface of contact, it was so minuscule and twitchy that I don’t see how it would be useful to a sewing task.

Possibilities:

  • I have no idea what I’m talking about with respect to circuits. Quite possible true
  • There’s a part missing which does the speed control. Doesn’t seem likely, there’s no obvious room for something that isn’t there anymore
  • The foot switch is just so old and used that the functionality I’m looking for has given up the ghost. Well, yes, but then I should be able to fix it. This seems a really simple device

Any advice is appreciated.

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2 Responses to Sewing Machine Problem

  1. david hallas says:

    The capacitor is missing

  2. Adabhael says:

    I found this today attempting to solve a similar problem and figured I would share what I have learned. I believe the capacitor was installed to prevent interference with AM radio/TV, and possibly not required for operation. I could not find that authoritatively, but I did locate one person who stated that the capacitor is surplus, although no comment on speed control without it.

    With regards to speed control, when I first opened mine, I also thought it must be a single-speed controller because of there seemed to be only either open or closed. However, in using my Singer 347 I did have ON!, but also an EVEN FASTER, and I got a hum with small foot presses, both of which seemed inconsistent with a single-speed control.

    SewingKiwi’s blog, I think this should be variable speed control, and is probably just dirty/corroded/making bad contact. I believe the plunger that moves in and out of the the white porcelain part is making contact with an carbon pile to provide variable resistance inside that insulated ceramic. The screws posts that hold with wire contacts must also provide a set of contacts for the carbon pile. Once the plunger reaches the end of its travel, it closes the gap with the visible copper contacts, which bypasses the whole carbon pile completely, resulting in a full “on” for maximum speed. Based on SewingKiwi, I am planning to disassemble and clean my controller, and then measure the resistance to see what I find.

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