Truing a Grinder Wheel

Phil3

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A novice question I am sure, but how does one go about truing a grinding wheel? Even the Norton wheel I have is like a potato chip on the end of a shaft. It wobbles in the axial and radial planes. I can minimize the left to right wobble with a better set of flanges (I tested this), but still not that great. More of a concern is that the the grinding surface moves in and out upon rotation. How does one make this surface run true? Using a dressing tool would seemingly just follow the uneven contour of the wheel. I suppose it can more heavily hit the high spots, eventually making the surface run true. Is that how this is supposed to work?

Phil
 
I have a HF toolgrinder with the green wheels. I machined my tables where they were square referenced to the groove the factory cut in the table. Now I can take a diamond dressing tool and align it in the groove and dress the wheel ever so slightly by hand. Then I take a Norbide stick to finish dressing and it seems to work well. I want to get some better wheels when I get the cash to really improve the grinder.


be
 
If you use the tool posts and advance the diamond dresser ever so slightly it will dress off the high spots and give you a true wheel. The side to side wobble is a bad wheel or poor flanges and I personally would check it very closely before I used it. Do you know how to give a wheel a "ring test"? That will help find any cracks on voids prior to a wheel disintergrating in your face or eyes. If you do not know how PM me and I will be very glad to explain it to you. Your safety is most important so don't hesitate.
Bob
 
Bob, thank you for your reply.

So you recommend the diamond dresser and not the star wheel? I have neither and want to make the right purchase. The grinder is a Jet 8" I bought new and the flanges are stamped steel. I faced these in the lathe with no improvement. Without getting into much detail, it is because the relatively thin flange was settling into a recessed area on the shaft that is not exactly running true. I made a test flange that was 3/8" thick with a snug fitting hole over the shaft and that helped the lateral runout a lot. There is still some, but nothing like before. Radial runout is still present obvoiously.

I suspended the wheels with coat hanger wire and tapped it with something (I don'[t recall) and it did not "thud". As I recall, it had some sort of ring to it. If you have tips on testing this, please do tell me. I am very safety conscious and that 8" wheel spinning to 3400 revs or so is scary. I always start the thing standing to the side and I let it spin for about 10 seconds before grinding anything.

Phil
 
To ring test a grinding wheel,hold the wheel through its hole with a screw driver that is loose in the hole. Tap the wheel with a plastic screw driver handle,plastic hammer,anything soft. The wheel will ring IF it has no cracks. If it does not ring,it is cracked and do not use it.

A star wheel will dress a wheel. It might be easier to use than a diamond as the diamond cuts with only a small point of contact. Ultimately,the diamond should leave the wheel sharper. You need some way to guide it straight,though.
 
Are you sure that the problem is the wheel and not the grinder? If it is the grinding wheel, I'd take it back to where you got it.
For a bench grinder I would use a star wheel. Don't try to dress the sides of the wheels.

Randy
 
Phil,

There should be no discernible axial wobble to the wheel and the flanges are likely not the problem. It sounds like your grinder may have a bent shaft. You may want to try running it without the wheel, or maybe even running an indicator on the shaft to see if it's bent.

Diamond dressers are not generally for hand use. An ordinary star dresser is all you need for dressing the wheel on a bench grinder.

Tom
 
The grinder shaft has virtually no radial runout and .001" at most axially (lateral wobble) where the wheel flange sits. Using a close fitting solid 3/8" thick flange substantially improves axial wobble. It was the radial runout I was not sure how to deal with.

The axial runout problem is due to the way Jet cut the wheel shaft. See the pic attached.

The undercut area on the shaft appears to have a small radius. This means that when you slide on the flange, it will not sit flush up against the larger part of the shaft. It slides down the radius and away from that part of the shaft. Put on the wheel and tighten it up, and you can visibly see a gap between part of the stamped steel flange and the face on the large part of the shaft. This would not happen if there was no radius there.

I tested this by making a .375" thick flange that fit nicely over the shaft. This meant the flange is now located by the shaft axis and its fit on the shaft, not the undercut area. This improved the axial wobble noticeably, especially after I machined a bevel on the inside of the edge of the flange hole to clear any part of that radius.

Would be best to machine the shaft, but not really interested in taking apart the entire grinder motor. And besides, wanted to make new higher quality grinder flanges anyway.

Phil

Grinder.JPG
 
Are you using the original flanges that came with the grinder? Possibly Jet has a proprietary flange for that model?

Randy
 
Looks like the roughing pass pulled in a bit as it hit the shoulder, or they deliberately undercut it in the roughout phase. I've seen many grinder shafts with that "feature". Most of the flanges are thick enough to not "fall" into the undercut, so it doesn't cause a problem, but if someone were to face off a bit from the outside of the flange, it won't bear on the finish turned area, but can fall into the undercut. This can cause some runout problems. Carefully making new flanges is an option if this applies to your case. A surface grinder is handy to ensure parallel faces on the flanges.
 
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