Turning Down a Motor Shaft

[EdK]

I have a 3-phase motor that has a shaft size of 24mm and would like to turn it down to 19mm. Has anyone done that and if so is it hard to do? I don't want to ruin the motor, obviously.

Thanks,
Ed


  2799.jpg (Size: 19.01 KB / Downloads: 167)

[November X-ray]

Ed - I had to reduce the shaft size on a motor last year when I could not find the exact replacement for my A/C unit. I took the shaft out of the motor and placed it between centers on the lathe, drove it with a lathe dog and used my tool post grinder to reduce both ends as the shaft was very hard (it has squirrel cages on both sides). I wrapped a couple of plastic grocery sacks around the armature and taped it up with masking tape to keep the grinding dust out. It's working well right this very minute as it is the main blower motor for my main air conditioner!

Good Luck!

[stevec]

I may disregard "Extreme" precision more that I should but I have several times just removed the armature, chucked the other end in the three jaw supported the "driver" end with a tailstock centre and turned the shaft to the desired dia.
Most times I've only had to mill or file down the key but once I needed to re-cut the keyway in the mill.
The KISS principle rules in my shop.

P.S. I'm still trying to think of a way to run the lathe in reverse in order to increase the dia. of a motor shaft (could make bearing changes dicey. LOL)

[f350ca]

I'd try Steve's method, but would look at boring the pulley first.

[Mayhem]

I'm with Greg, I'd look to modify the pulley first. You didn't say if it was a new motor but if it is, turning down the shaft would void your warranty.

[Tony Wells]

The second shop I worked in did all the machine work for a nearby electric motor shop, so we got a lot of metalizing and shaft repair /replacement. If you wanted, for any reason, to maintain the original shaft, they are pressed in and can be removed and replaced with a newly made shaft of whatever size you want. Otherwise, a 4 jaw with pads, and a good bearing center is sufficient to turn it down. Watch that you don't reduce the seal area if the motor has a live seal on the shaft, and be sure to leave a 1/32" minimum corner radius where you shoulder out. And you may have to recut the keyway, or at least need to make a non-standard key.

If possible, boring the sheave/pulley would be preferable.

[EdK]

Guys,

Boring the pulley is not an option. There is not enough meat in the smallest step of the cone pulley to allow it to be bored out to 24mm.
The motor is new but it's been sitting around waiting to be installed so the warranty has run out on it.

Ed

[jhovel]

Have a go at the motor shaft with a file. Chances are that it is soft, in which case you can turn it down between centres. Also, if your lathe is big enough, you only have to take the fan cover off and let the motor frame just hang there - it has bearings. At a few hundred rpm you won't hurt anything.
Cheers,
Joe

[stevec]

(06-07-2012, 06:27 AM)jhovel Wrote: Have a go at the motor shaft with a file. Chances are that it is soft, in which case you can turn it down between centres. Also, if your lathe is big enough, you only have to take the fan cover off and let the motor frame just hang there - it has bearings. At a few hundred rpm you won't hurt anything.
Cheers,
Joe

Have you ever come across an electric motor shaft that is too hard to turn down on a lathe?

[dallen]

have seen a lot of electric motors in 30+ years of working on Asphalt plants from 1/2 HP all the way up to 300 HP ones never seen one that a file wouldn't cut the shaft to file nicks and burrs off of.

me I'd take it apart and turn the shaft down.