Fixing a Foredom Footpedal
Q: I’ve got an older Foredom flex-shaft, but the foot pedal doesn’t work well anymore. It’s basically either on or off now, and the top speeds seem to have disappeared. Can these be fixed, or should I replace the whole thing?
A: If your old Foredom is one of the old simple CC models, then perhaps the foot pedal is the old cheap “carbon pile” type. Those are a simple design that does not last forever, but unlike the more recent electronic controls also sold, it can be tweaked sometimes to get a bit more life out of them. Whether it’s worth doing is another question, perhaps mostly one of budget. The Lucas control you can buy is so far superior to others as to be seriously worth your attention, but of course, it’s not free. If you’ve the budget for one, you won’t regret it. But if you’re forced to try and revive the old one, then here’s the method.
These old pedals consist of a ceramic block with a hole down it, a contact at one end, and a spring loaded contact, attached to the pedal, at the front, the other end. Taking up the distance between them, stacked in the hole, are a whole bunch of disks of graphite. When you press on the foot pedal, you compress that stack, improving the electrical contact between each disk, and thus the conductivity of the whole stack, and this provides the variable resistance that changes the motor speed. Over time, friction and wear and tear and electrical arcing reduce the thickness of some or all of those disks, making it hard to fully compress the stack enough to get full speed again. If you had multiple bad pedals, you’d then take some disks from one, and add them to another, increasing the thickness of the stack again. Not as good as new, since the disks are still worn, but it works for a time. If you don’t have an extra pedal to sacrifice, then do the same, but use disks cut from sheet copper. Add a couple, reassemble the control, and try it. If it doesn’t yet give full speed, repeat. If it only gives full speed, without the lower speed range, remove a disk to loosen the stack a little. If the problem is just that the pedal sticks, then a bit of oil at the appropriate pivot points helps.
In testing the pedal, do be sure to fully reassemble the thing before plugging anything in. Remember that you’re working with full 110 volt current here, so play it safe. All in all, it’s a bit messy, but it does work for a while. Now, if the control is one of the electronic types, including the feedback types used with series R motors, then the cure amounts to replacing the inner guts of the pedal. The parts can be ordered from Foredom. If that’s the situation, then look closely at the Lucas pedal again. it’s more costly initially, but they are so much more durable that the increased initial cost will be paid back in greater life span, as well as giving you a better pedal. It’s simple enough to open the pedal up and see, since if it’s dead now, you’ve nothing to lose.
If, inside the thing, you find any electronics components, transistors, resistors, and that sort of circuitry, then toss it. If it’s that ceramic block with the carbon pile, then if you like you can try rebuilding it. The foot pedals are not generally made to be frequently dismantled, which is why there are no obvious screws. It’s been a while, but as I recall, there’s a tab at the back edge of the bottom which you bend out of the way, and then slide the bottom off. At least that’s my memory.
At the same time, also pay attention to the motor itself. Sometimes, an apparent bad pedal is also due in part to a worn motor. That is often due to overly-worn motor brushes. When they get worn down too much, the motors can become balky. Those parts, fortunately, are cheap to order and easy to replace. Just look down into the end openings when the motor is running. Check for excessive sparks and arcing, or an electrical “burning” smell. Then unscrew a brush and look to see how much length is left—if it’s down to a nub, you need new ones. When replacing it, pay attention to the direction of the curve in the end, putting it back as it was before.
Sometimes, the problem is more serious, with the commutator itself being overly worn and grooved. That’s harder to see and diagnose without taking the motor apart. That portion too can be replaced, but frankly, when the motors get that far gone, I find they don’t have much life left in the bearings or other parts either. So at that point, it’s time to replace it. But if you want good slow speed control, then you really want the Lucas pedal; it excels at that. The carbon controls are OK when new, but after being rebuilt they get less sensitive. You might as well try it, since doing so will cost you just a little time and effort, but I’m betting you’ll not be totally satisfied with the result if you really want good slow speed sensitivity. But try it. Who knows, you might get lucky.
by Peter W. Rowe M.F.A., G.G.