[E-Revonut]

depending on the amount of torque that will actually be required to get the train moving you may not need to grind a flat spot for the set screw, it will still bite into the round shaft and stop it from spinning. However if you wish to make a flat spot there are a few ways to do it. Start by getting yourself a plastic bag such as a sandwich bag. put the motor in the bag and poke the shaft through, this keeps any metal filings from getting in the motor. If you have some quality files and the shaft isn't to hard you can do it that way. Or you can use a dremel tool with a grinding stone on it to grind a flat spot.