After not using my Nichols Lathe for an extended period, I plugged it in. I typically use the speed control to operate the lathe. By chance I happen to use the on/off switch the turn the lathe off. The switch failed to turn off the motor. Removed the switch, and the motor ran.
Several Years ago I had a pdf of the manual, but that went with a crash hard drive. I won't be able to get the controller box until this weekend(it's up against a wall.
Are there any ideas?
I'm sorry for being kind of slow, but I am not quite sure that I am following what happened.
Switch contacts certainly can weld together when used with an inductive load (motors and other electromagnetic devices). It happened to me once with my old Delta lathe. I flipped the power switch to turn it off and it kept on going. So, I just unplugged it. I did an autopsy on the switch and found that the contacts had stuck together and then everything inside the switch basically fell apart.
Your last sentence is confusing me -- "Removed the switch, and the motor ran". Obviously, there is more to the story, but I would only be guessing at what it is. Would I be right in guessing that you disconnected the wires to the switch and then jumpered them together so that you could run the motor? If my guess is right then I suppose that you want to repair the lathe with a new switch.
You can't use just any switch -- well, actually you can, but if you would like one that is more reliable then make sure that the replacement is one that is rated for inductive loads and twice the maximum current of the motor. Switches that are designed for use with motors are different internally than switches used for ordinary applications like lighting. They have larger wider spaced internal contacts that have a much faster snap action in order to minimize arcing. Arcing is what welds the contacts together. Somebody took note of that fact many years ago and invented the arc welder.
Here is my guess on why the switch failed when you changed the way that you turned the lathe off. If you normally ran the speed control down to minimum and the turned it off, the motor is not drawing much current so there is not much arcing going on between contacts. This last time, the motor was running at high speed and you flipped the switch to turn the lathe off. When the motor is running fast, the current is much higher -- also one other very important thing -- there is a LOT of stored energy in the motor's magnetic field. When you flipped the switch to OFF, that stored energy has to go somewhere -- that "somewhere" would be to keep the current flowing through the motor's wiring -- the collapsing magnetic field will produce whatever voltage necessary to bridge the gap in order to maintain current flow through the contacts so that the motor is able to dump its stored energy. All of this happens almost instantly from a human perspective, so the gap is still very small when the arcing occurs -- and, sometime there is enough molten metal on the contacts to form a weld.
