Grinding Shims

[old_chopper]

Lots of difference between the precision of a surface grinder and a dremel tool. I know what my precision level is (or isn't) with a hand tool such as the dremel mentioned. It's your bike and your choice.

[Steve]

I'd do a thing like that as a temporary fix to get home (not that I've adjusted shims on the road).

I have, sort of.

OK, it wasn't on the side of the road, but I did do an adjustment in the hotel parking lot a couple of months ago.

Clarification: Instead of ordering new shims, my mechanic has a machinist that will correctly work the existing ones to the spec needed for re-installation.

Still has that level of UNcertainty that I would rather not choose to accept.

.

[Nessism]

Lots of difference between the precision of a surface grinder and a dremel tool. I know what my precision level is (or isn't) with a hand tool such as the dremel mentioned. It's your bike and your choice.

I agree with this. The only way I'd use a hand ground shim is if it measured flat using a micrometer, not a caliper, and not just eyeballing it either.

[amontyg]

Thank you everyone for your comments, I have been persuaded to just get a new shim at the correct size.

I have had the shim in for three days now, and it seems to work fine, but just to be safe I think I'll park it and wait for the correctly sized shim to come.

[Allie]

....and thank you all for confirming that I don't want to use some home ground shims I inherited that have a 3-4000th in. variance in them. I'll donate those to the Shim Club, since Ray has a precision grinder. I do have two home ground shims that measure perfectly uniform (at least as uniform as a factory shim anyway) with a micrometer, so I'm not worried about them.

[mvalenti]

I agree with this. The only way I'd use a hand ground shim is if it measured flat using a micrometer, not a caliper, and not just eyeballing it either.

Not to be picky, but, you cant measure "flat" with a micrometer.

[wally]

I would be nervous to grind down my own shims.

They are a bit of a rarity here, so my next door neighbour has a shim grinding machine (he owns an engine rebuilding shop) and did mine for me to specs required.

He gets tons of requests from bikers for shim grinding.

Worked out about 1/4 price for second hand ones, plus then I would have to trade in my old ones.

[mvalenti]

We have grinding machines here, but on the one I tried didnt get the results I expected. Upon further investigation our wheel was in serious need of dressing. When work slows, I'm going to haul my arse in there and try the other machine. Hopefully if I am successful, I will be able to help the shim club out with more usable sizes.

[WShie]

I am a machinist and have ground my own shims on the surface grinder. I only had to remove .0005" from one and .001" from another. I then installed them with the ground side towards the bucket- no problem. My only problem was demagnetizing before installation. I see no problems if you don't take an excessive amount off the shims; if they are case hardened and I'm not sure if they are or not. But you must use a surface grinder to ensure that they are truly flat. A Dremel or any other hand held tool doesn't get it. That's like a doctor performing surgery with a steak knife; you can do it but it's not right.

[mvalenti]

I am a machinist and have ground my own shims on the surface grinder. I only had to remove .0005" from one and .001" from another. I then installed them with the ground side towards the bucket- no problem. My only problem was demagnetizing before installation. I see no problems if you don't take an excessive amount off the shims; if they are case hardened and I'm not sure if they are or not. But you must use a surface grinder to ensure that they are truly flat. A Dremel or any other hand held tool doesn't get it. That's like a doctor performing surgery with a steak knife; you can do it but it's not right.

Agree'd Surface grinder is the way to go. I did take one shim and threw it on the lathe which worked well also. This lead me to believe that they are in fact not case hardened at all... See attached picture.

[Allie]

Not to be picky, but, you cant measure "flat" with a micrometer.

True from what I know, but when the reading is the same at every point you measure on the shim I'd be inclined to call the shim 'flat' for all practical purposes. Is this wrong?

[mvalenti]

Yes, it is incorrect. With a scenario of a crowned shim you might not detect it with a micrometer much less a caliper. This is in part due to the relatively small surface area of the micrometer anvil and spindle. Flatness measurements are done on a surface plate (fancy for some really really flat surface) where intimate surface contact of the part is observed (Surface A). A gauge travels along the opposite surface (Surface B)all the while readings are observed to measure flat and parallel to the first surface (Surface A). When shims are ground, they are typically done by removing material from both sides. So, can you measure shim thickness with a micrometer, yes. Can you trust its flat, No.. But thats ok.... put the shim on a glass plate, does it sit flat or rock? flip the shim, repeat... you will observe flatness, or lack of...

[Allie]

I assume that a micrometer is not capable of measuring the degree of consistency of the procedure you describe, but my question is; in the intended application does it matter? What are the allowed tolerances?

[Allie]

Maybe some clarification: I didn't grind these but they were done on a flat surface grinder. A dremel could produce wildly erratic results, but this job is smooth, just not always even.

[chuck hahn]

Allie..if they were done on a surface grinder, then I can assert they are flat and consistent throughout. I was a die maker for 25 years and I ran a surface grinder daily..and sometimes for days on end making specialty parts and fixtures. Yours are good to go.