Cup Grinding Wheel Imbalance

[Jon GibbsParticipant @jongibbs59756]

Hi All,

I've just bought a 100mm flared cup grinding wheel from Midland Abrasives to put onto my offhand grinder.

I'm following the procedure Harold Hall suggests in his two books "Milling a complete course" and "Tool and Cutter Sharpening" and have made up a new set of reducing bushes. The bushes run true and are within a gnats of being in-balance.

…but when I mount the wheel it runs way out of true with one side noticeably thicker than the other. I've tried dressing the inside of the cup to make the sides more or less the same thickness but the grinder still vibrates like heck.

Is this normal for cup wheels?

Jon

[Jon GibbsParticipant @jongibbs59756]

[not done it yetParticipant @notdoneityet]

Is this normal for cup wheels?

It should not be. Vibration is likely to shorten the life of the whole machine. Not good, and extra stresses could eventual (sooner or later) failure

[Andrew TinsleyParticipant @andrewtinsley63637]

I would have returned it to Midland Abrasives, but probably to late now that you have tried to make it balance. A cup wheel should not have these defects. I would not even run it in the state you have it. Far too dangerous, I have had one wheel explode on me and it isn't a pleasant experience!

Best of luck,

Andrew.

[Chris Evans 6Participant @chrisevans6]

Does your bench grinder shaft have a decent register/step between wheel fit and main shaft diameters ? I had to strip my grinder and correct the shaft to get the wheels running well even with new flanges, the run out gave the impression of out of balance.

[Jon GibbsParticipant @jongibbs59756]

Hi All,

Thanks for the comments and suggestions.

A new 125mm saucer wheel I bought at the same time and using the same style bushes runs beautiful and smooth.

Chris, I have added a new 1" diameter step trued up in situ on the shaft and the shafts run true within 0.001".

Jon

[Jon GibbsParticipant @jongibbs59756]

Well last night I spent some time with the DTI and realized that the inside and outside mounting faces of the wheel and the blotters were not parallel. The outside face was flat and more or less on-axis with the outside but the inside face sloped around 0.015" – 0.020" across about 2.25". So, I cut some paper annular shims, trimming and stacking them to take up the misalignment – finally trapping them between the blotter and the inside bush. It was a real fiddle to get them as close as possible.

Anyway, the upshot of this is that the wheel is now running much better. The outside rim has a TIR of about 0.005". Still not perfect but the vibration is within reasonable limits for me and I am able to dismount and remount the wheel fairly repeatably without too much trouble. I also ran the wheel for several minutes at full speed standing out of line and finally plucked up the courage to do some grinding. It worked ok.

I think that the dressing I did on the inside face helped even things up but there is still some difference is wall thickness around the outside of the cup which is responsible for the vibration.

Thank you for the comments

Jon

[not done it yetParticipant @notdoneityet]

That item was clearly not fit for purpose. The vendor would not like to hear of an accident with one of their products that was so poor that it needed shimming to run even close to balanced. "Better" is subjective – I would not accept it being anything other than true and vibration-free..

Contact them and get it changed is my advice. Any half-decent company will change it. Midland Abrasives are far better than half-decent, I would think, and would be pleased to replace that dodgy cup wheel.

[colin branniganParticipant @colinbrannigan54160]

I bought a taper cup wheel 100x40x31.75 5A 60JV from Midland a few weeks ago and having read thread prompted me to check mine and it had same problem, the other plain grinding wheels I ordered were okay.

Colin

[mark smith 20Participant @marksmith20]

I would have thought they would get into trouble with H/S etc… for selling things like this that aren`t safe to use.

[peak4Participant @peak4]

Posted by mark smith 20 on 03/10/2017 18:55:32:

I would have thought they would get into trouble with H/S etc… for selling things like this that aren`t safe to use.

I can't imagine it happened knowingly; I'm sure if one of the purchasers contacted them, they should consider a batch recall before someone gets hurt.

Bill

[colin branniganParticipant @colinbrannigan54160]

I have just sent them a email making them aware of the issue.

Colin

[Jon GibbsParticipant @jongibbs59756]

Hi Colin,

I thought that mine was probably the same but in fact my wheel had a slightly different spec.

It was a 100x40x31.75 8A 60KV Type 11 Taper Cup.

I probably should return it to Midland Abrasives but I've now invested at least a couple of hours into getting it trued up and it does seem to be running ok now.

Jon

[Ian S CParticipant @iansc]

Is the inside of the cup running concentric with the out side?

Ian S C

[Jon GibbsParticipant @jongibbs59756]

Mine is more or less running true now since I dressed the inside.

…but before that I would say that one side of the cup was at least 1mm thicker than on other and so it couldn't run true both inside an outside at the same time.

Jon

Edited By Jon Gibbs on 04/10/2017 10:16:48

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