I'm building a grinder, which consists of a shaft on which the grinding wheels sit, and the shaft is driven by a universal motor out of a washing machine via a belt and a pulley.
I'm using an off-the-shelf SCR speed controller. What I'm finding on the first test run is that the motor slows down a lot when I, e.g., try to sharpen a chisel on the grinding wheel. I can turn the knob on the speed controller up to get it up to the speed I want while sharpening, but then as soon as I take the chisel away, the motor starts to spin up and I have to turn the speed controller down to stop it spinning out of control.
I realise that this is probably the expected behaviour for such a motor, and you may very well tell me that I'm using the wrong motor for the job, and that a motor such as those in my bandsaw, sander, and drill press is what I need (I don't know what that type of motor is called). But this is what I have, and I like using things that I have already, unless it really turns out to be too complicated.
So, is there a simple (or less simple, but not ridiculously complicated) way to make the motor run at a more or less constant speed regardless of the load? I'm open to mechanical or electronic solutions (the motor has a tacho coil), either off-the-shelf or DIY.