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.
Go with the grinder. It will be quicker and safer. Make the cut with the motor off. Then spin it up and use the grinder to dress it to your satisfaction. Should be able to get an almost lathe-cut finish.
One of our godfathers of phase converters, Fitch, now accessible only through google archive searches alas, cut off the excess shaft on his idler motor. I always got the impression he removed the armature from the motor, mounted one end in the lathe chuck, supported the other in the steady rest, and did a cutoff operation. That's certainly how I'd try it. Three phase motors are much easier than single phase motors to disassemble since there's no fiddly centrifugal switch.
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.
Don't forget to protect the bearings/bushings and seal off any openings into the motor housing. It will be difficult to stop abrasive dust getting past the shaft, particularly since you are trying to cut the shaft off flush. Try packing a piece of string soaked in heavy grease into the gap.
No matter what RPM the motor runs at under its own power, it will be WAY too fast for the proper speed on the hand hacksaw blade. Why not just hacksaw it off by hand, say over a couple of days with a couple of minutes sawing whenever you feel like it, and then,as another reply suggested, with the motor running, dress the end with the angle grinder.
If you're going to be making stuff out of steel, you will find this extremely useful. I have a Milwaukee, but Jeff W. sez this HF saw works great for him == for about 1/5 the price of a Milwaukee.
This would cut your 1-3/8" shaft in about 30 seconds. It'll go thru
2 x 2 x 1/4 angle a lot faster than that, leaving a clean cut with no burrs.
I think that I will buy it... Thanks... Incidentally, I was looking at it earlier this morning and was contemplating buying it, but was not quite sure.
Please give our best and congratulations to Fitch and his good wife (Ardra??? or something like that..I've "lost" my old who's-who list to find her name). Heck of a job for them both, I'm sure.
Love to see some pix of what it looks like, after the amazing description of a few years back. and when he's got time, a story or two about the fun he had doing it, as he was always good with the telling!
Her name is Nedra. I've forward y'alls good wishes. He may check in, who knows. I told Fitch the NG has kinda gone to hell with OT crap causing contributors like Jerry Martes and John Stevenson to check out. I also noted that Gunner has become a net contributor, must be mellowing some. Gettin' some gray in yer whiskers, Gunner? Humility (not craven submission) is not learned young, is learned by adversity. Wisdom is not possible without humility, not to say that humble men should not have arms as they might deem necessary.
No lack of soapbox OT crap (Cliff) to fill the void.
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