Ignoramus26153 wrote:
I have a 7.5 HP electric motor, with what looks like a 1 3/8" shaft
(213T frame). I will use it as an extra idler on my phase converter,
to be spun up when the main idler starts.

I would like to cut the visible part of the shaft off completely.
Cutting the shaft off would allow me to put the motor into any corner
of my garage without any enclosure, without worrying about things
wrapping around the shaft etc.

The question is how to cut off the shaft. A couple of possibilities
come to mind, one is to spin up the motor and use a hacksaw, another
is to use a angle grinder. The first seems more fun but also more
dangerous (hacksaw getting caught up in a powerful motor), the second
is less fun and may not get a cutoff as clean, leading to vibration.

I wouldn't try the first one. The blade will probably jam when the teeth
catch on the keyway, or it may jam because the chips aren't being
released. Either way it is quite possible that the blade will break and
become embedded in your arm, leg etc. :-D

To be honest, I wouldn't cut the shaft off because it makes the motor
useless for anything else. I'd probably make a cover from a disc of
steel plate and a length of pipe welded together and attach it to the
threaded rods which hold the motor together. Or attach the guard to
whatever you mount the motor on.

If you do feel the need to cut off the shaft, the angle grinder is a
better bet. Depending on the design of your grinder, you may be able to
guide the grinder by resting the guard against a heavy wooden board. In
this case you would need to find a way to securely clamp the board to
the motor at 90 degrees to the shaft. You'll also need to prevent the
shaft from rotating. I know it seems obvious, but remember to use a
cutting disc for cutting and a grinding disc for grinding.

If I had to do this I might use a hand hacksaw. I'd mark the position of
the cut using a scriber, then remove the rotor and clamp it securely.
Then I'd wrap a strip of paper around the shaft as a guide to help me
keep the cut square. I'd then cut slightly to the side of my mark so as
to give me room to clean up the end using a file.

If you have access to a huge lathe you might be able to remove the
rotor, hold it in the chuck and shorten the shaft using a parting tool.
This would probably give you the neatest cut.

Best wishes,

Chris