machining should square

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SteveM
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machining should square

Post by SteveM » Thu Apr 11, 2019 10:52 am

I picked up a Dayton 6" bench grinder and the washers hold the disks on were just plain stamped flat washers, so I swapped them for machined ones with relief.

Once I did that, there was a pronounced wobble in the wheel. When we loosened the nut, the wobble went away.

The wobble is caused by the shoulder on the inside of the wheel not being square.

I could take the armature out and machine the shoulders square on the lathe (there are centers in the ends), but I'd like to avoid pulling it completely apart.

Any suggestions on how I could square up that shoulder?

I was thinking that a tool that worked like a pencil sharpener with the cutting edge on the end would work, or if I had one of the right size, a hollow mill.

I could clamp a toolholder to the rest, but I'm not sure how rigid that's going to be.

Steve

chief
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Re: machining should square

Post by chief » Thu Apr 11, 2019 11:05 am

Well, the smart folks here will most likely tell you I'm crazy, but if it were me......

If your lathe has enough swing, I would just mount the entire motor, cover the cooling holes with tape, and turn it in place.

It would probably be best to run the lathe in reverse, with an upside down tool, so that the motor "want's" to rotate to the rear of the lathe.

Terry

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DianneB
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Re: machining should square

Post by DianneB » Thu Apr 11, 2019 11:07 am

I find it hard to believe that the shoulder on a turned shaft wouldn't be square - seems like it would be hard to make a shaft with an out-of-square shoulder. I'd be looking hard for something else!

Using a precision square, check that the face of the step is machined perpendicular to the shaft extension and that the extension is running true to the bearings.

What is your machined washer resting on - the extended shaft, against the shoulder?

I am inherently lazy but if I had a problem with the shaft, I would dis-assemble the grinder and turn the shaft between centres (which I presume is how it was made in the first place. Maybe it got dropped in transit and the shaft is slightly bent?

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SteveM
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Re: machining should square

Post by SteveM » Thu Apr 11, 2019 12:26 pm

chief wrote:
Thu Apr 11, 2019 11:05 am
Well, the smart folks here will most likely tell you I'm crazy, but if it were me......

If your lathe has enough swing, I would just mount the entire motor, cover the cooling holes with tape, and turn it in place.
I think the phrase "It's so crazy, it just might work" applies here.

I could just put a strap on the motor body to keep it from spinning.

Steve

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SteveM
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Re: machining should square

Post by SteveM » Thu Apr 11, 2019 12:33 pm

DianneB wrote:
Thu Apr 11, 2019 11:07 am
I find it hard to believe that the shoulder on a turned shaft wouldn't be square - seems like it would be hard to make a shaft with an out-of-square shoulder. I'd be looking hard for something else!
I pressed the washer against the shoulder and turned the other end of the shaft and I could feel and see the washer wobbling with each revolution.
DianneB wrote:
Thu Apr 11, 2019 11:07 am
Using a precision square, check that the face of the step is machined perpendicular to the shaft extension and that the extension is running true to the bearings.
The step is very small, probably between 1/32" and 1/16", so not much room to check with a square. I could clamp the washer down and check the washer surface.
DianneB wrote:
Thu Apr 11, 2019 11:07 am
What is your machined washer resting on - the extended shaft, against the shoulder?
It's on the shaft pressed against the shoulder. The face of the washer is a machined face, not stamped, so it's true (and we tried it with several to confirm).
DianneB wrote:
Thu Apr 11, 2019 11:07 am
I am inherently lazy but if I had a problem with the shaft, I would dis-assemble the grinder and turn the shaft between centres (which I presume is how it was made in the first place. Maybe it got dropped in transit and the shaft is slightly bent?
If you don't tighten it up (literally just a quarter turn loose) it doesn't wobble, as it is resting on the shaft and not on the shoulder. If you run the motor, the end of the shaft is not wobbling.

Steve

Mr Ron
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Re: machining should square

Post by Mr Ron » Thu Apr 11, 2019 1:52 pm

First I would check that the hole in the grinding wheel is concentric. If it is, check with a different wheel. If wobble still occurs, I would "mickey mouse" a setup to turn the arbor, using the motor itself as the lathe. Taking the grinder apart and turning the armature/arbor on a lathe, isn't a big job, but I would take the "mickey mouse" approach first.
Mr.Ron from South Mississippi

earlgo
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Re: machining should square

Post by earlgo » Thu Apr 11, 2019 2:09 pm

If you knew someone with a tool and cutter grinder, you could mount the motor on the table perpendicular to the wheel, turn on the motor and turn on the grinder and proceed to square up things.
Something like I did to the buggered up motor shaft and subsequent sleve.
Grinding the motor shaft.jpg
grinding motor shaft
Grinding the sleeve od.jpg
grinding sleeve.
Worked great.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

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BadDog
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Re: machining should square

Post by BadDog » Thu Apr 11, 2019 2:09 pm

Maybe make another inner washer that has a reasonably long bore and is a snug slip fit. That way it is shaft located and square, and the shoulder isn't responsible for squaring. If, like like with my 7" grinder washers, you are using a larger hole wheel anway, you should have plenty of bore length to locate the wheel well within the range of dressing true.

If not, and it still wants to misalign when snug, maybe rough up near the shoulder and apply some JB weld or the like. If you want to be able to remove the washer easily, apply some sort of release agent and install the washer by hand without clamping. The epoxy should level that surface and prevent the washer from tilting when you attach the wheel and nut.

Or, as previously suggested, just true it in situ. Maybe with a hand file with safe edge (ideally on the wide side) against the shaft and used on a support to square that shoulder.

Or, if all is exactly as described, the right fix is take it apart and true it up between centers. If it were a high grade grinder that I wanted to keep forever and use a lot, that's the right call. If it's like several cheap junk grinders I've got just for mounting things like various wire wheels, 3M deburr wheels, and other such things. And I wanted to use it for rigid wheels too, I would more likely go with option 1, 2 or 3 as the grinder itself isn't worth the time for a high quality fix.
Russ
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jcfx
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Re: machining should square

Post by jcfx » Thu Apr 11, 2019 2:20 pm

Is there enough room behind that shaft shoulder for a interference fit bushing ?
You could turn and bore one and heat the bushing to slip right in and have a true face for the washers.

I don't think Terry's idea is that crazy, if it's a small amount that you have to turn to get a square shoulder.

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SteveM
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Re: machining should square

Post by SteveM » Thu Apr 11, 2019 2:30 pm

BadDog wrote:
Thu Apr 11, 2019 2:09 pm
Maybe make another inner washer that has a reasonably long bore and is a snug slip fit. That way it is shaft located and square, and the shoulder isn't responsible for squaring. If, like like with my 7" grinder washers, you are using a larger hole wheel anway, you should have plenty of bore length to locate the wheel well within the range of dressing true.
I thought of doing that, and having it locate on the area behind the shoulder, but that area is a bit rough. Might just be some rust and hitting it with a file would level it off. Having it just on the part under the wheel would probably do it. The wheels currently on it are 1" bore with plastic sleeves.
BadDog wrote:
Thu Apr 11, 2019 2:09 pm
Or, as previously suggested, just true it in situ. Maybe with a hand file with safe edge (ideally on the wide side) against the shaft and used on a support to square that shoulder.
We tried that, thinking it might just be a burr, but the file just followed the contour.

Steve

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Re: machining should square

Post by Conrad_R_Hoffman » Thu Apr 11, 2019 2:59 pm

Maybe make a cast iron sleeve then use that with some compound to lap the step?
Conrad

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John Hasler
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Re: machining should square

Post by John Hasler » Thu Apr 11, 2019 3:01 pm

I'm with Dianne. There isn't much to taking one of those motors apart.

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