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Electric motor endbell machining

Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
I was reading the thread about old VS new electric motors and it got me thinking about some work I do.

I sleeve motor endbells occasionally for a rewind shop when they get real busy. A lot of the time the bores probably aren't any worse than what they were when they left the factory that made them. The shop always gives me the bearing fit specs and I can usually hit them fine, but what bothers me is how flimsy the endbells are and how tight the fit tolerances are. I don't think the shop can actually measure what they ask of me.

Sometimes I have to get pretty creative to hold onto the endbells without distorting them too much. I think any distortion will effect the bore job and I'd wager that the whole mess distorts when the motors are final assembled because the housings and frame aren't true.

How do other's handle this kind of work? I'm fine with just doing what they ask of me, but are there other steps that should be done- Like truing up all the mating surfaces- Before endbell bearing bores are cut/sleeved?
 
The mating surfaces of the end bells ought to be quite true. There is a spigot for alignment, and an adjacent surface that contacts the end of the body. Those should be the reference for fixturing the end bell for working on the bores. Motors have some self aligning in the bearings, but the rotor has a fairly close fit inside the stator, with a few thou clearance, so overall tolerances are reasonably close to avoid rotors dragging on the stator core.

naturally, that may be different between cast motors and motors with stamped and rolled bodies. The cast frames would likely be a bit better tolerances. I think just about all end bells are cast, even for the stamped body case motors. Some are cast alloy parts, and very thin, I bet those move around like crazy.
 
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I have watched how it is done, ( I work for marathon) and we measure in the machine for the bore and frame step. Take it out, it moves. Bolt it up, it moves. Don’t tell the Design or quality guys, they can’t get their mind around it.
Joe


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Pi tape.

Oh how I hate the ^%$#@! things.

As far as checking concentricity to the bearing bore (from the rabbet fit)
You'll have to put it on the motor frame, or a rabbet ring.
 
Pi tape.

Oh how I hate the ^%$#@! things.

As far as checking concentricity to the bearing bore (from the rabbet fit)
You'll have to put it on the motor frame, or a rabbet ring.

hah... great idea.... the "rabbet ring", kinda like a torque plate, make to fit the bell, hold by that, with the bell screwed down to it. Worth it if you get a bunch of them of the same size.

I was figuring the rewind shop would not mess with little motors, so you would pretty much only get cast iron frames, but maybe not.
 
I don't know the HP sizes, but yeah, they're bigger. I'd guess 15-50HP sizes. All cast. All different, but the bearing sizes are pretty standard- As in there aren't many different bore sizes.

The motor shop has cast sleeve material they provide or I make a sleeve from steel. They say no loctite. I do a heavy press for the sleeve and bore it for the bearing fit.

I guess The "Rabbit plate" or "Torque plate" was what I was thinking, but I don't think the motor shop gets it. They don't want to pay for that.
 
The "rabbet plate" would be more hassle for the bells that have the bearing fit on the inside. My old motorss have the bearing in a housing that goes on from outside.

I suppose the plate would have to be a bit oversize, and shorter for convenience, to hold the bell in position to work on the inside as in the video. The video has the bell held by the shaft hole, which seems to have worked, but that hole is clearance, and might not be concentric. The casting was wobbling, but the rabbet was steady, so it was at least visibly centered.

What does that have to do with motor end bells?

In the first part he is sleeving an end bell for a new bearing, the recess got wallowed out oversize.
I
 
Where might a few sets of soft top/pie jaws fit in to keep the machining costs down.

The price of a lathe large enough might be an issue ;-)

I've got a set of "electric motor reamers", but they are for align reaming of bronze plain bearings.
 
How do other's handle this kind of work? I'm fine with just doing what they ask of me, but are there other steps that should be done- Like truing up all the mating surfaces- Before endbell bearing bores are cut/sleeved?

I would just make sure there were no burrs or raised dings on the pilot diameter & the clamping face. As mentioned above, these end bells move around easy. Large end bells in a regular engine lathe can be frustrating to dial in. Machining with the boring bar really far out from the toolpost isn’t much fun either.

For a while I was getting bells from a company contracting railroad refrigeration car repairs for the diesel to genny setups. At 2+ foot diameter & 12”ish flange to bearing bore depth they went better with my devlieg (horizontal boring machine) and clamping the flange face up to knees while setting on a 123 block on the table. The knee’s side and back faces were square to the table (machined as a set).

Setting up that way you have to pull from the top some to make the bell pilot round. I used a 500# dillon scale clamped to the top flange pulling 30-35#’s & when the pilot diameter was right in “Y” and the pilot bottom still loading the 123 block on the table I’d push the pilot hard to the left knee & clamp the flanges.

Takes longer to type than to do it after the setup is made, as the bells were all the same. Those guys did allow locktite, and sleeve OD’s were pre-machined in A-B-C sizes. Using 680 bearing locker you could bore 5 minutes after the sleeve fixture’d and I’d usually do 3 bells per hr without having to run hard.

If they’d were shrink or force fits then I could have pulled a sleeve in bells having a hole in the end. The blind end bells however would likely have had to come out & go in the press if I stuck the sleeve while assembling… No way I’m trying to use the machine tool for pressing.

Good luck,
Matt
 








 
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