View Full Version : How does this pedal work?

tony ennis
11-24-2007, 03:20 PM
My wife has a foot pedal that is a speed control for a bobbin winder. It stopped working. The general idea is that the pedal pushes a flat spring-like contact against a captured round rod. The spring and far end of the rod are connected to power. The rod is captured in a ceramic case. I took off the capturing plate, and the "rod" was hundreds of thin graphite disks! What a mess! Only the end of the rod was a solid piece! How does this work? The more you squeeze them with the pedal the lower their resistance?

The reason it stopped working was probably a workmanship defect - the metal piece that forms a hinge for the spring is held to the ceramic case by two rivets. They were loose. The hinge separated, the springs escaped. While attempting to tighten the rivets I broke the ceramic which was remarkably fragile it seems. It was a clean break, the glue is drying now :(

Herm Williams
11-24-2007, 03:32 PM
That is a standard sewing machine speed control. Cost about fifteen dollars the last one I purchased, about a year ago. These work by compressing the graphite making it less resistant. Sewing center or ebay has them.