Cutting Shim Stock

Rather than cutting and stacking multiple shims, how about measuring the clearance needed with some plastigage? That way you could make a single shim (set) of suitable thickness. Or at least one thick shim, that could then be fine tuned with one thin shim.

I believe plastigage is available for checking clearances up to around .070".
Just a thought. :)
 
I'm looking, but not seeing, the need to cut the shim in any shape other than a rectangle that wraps the outside of the bearing insert. You said an elongated U shape, but I'm just not seeing it. I'm thinking that the bearings look like automotive main bearing inserts, but that may just be my eyes. If they are like that, why cut a profile? If there is a tang on the cap, I guess you could notch out to make sure it didn't snag on the lower shim. Is that what you are trying to do?
 
I hope I'm not being just dense, but I think normally shims augment the thickness to compensate for wear, so they just fit between the bearing shell and the cap. Or they are too tight, and then the cap get's shimmed apart a bit. What am I missing?
 
OK, I can see that. Still, shouldn't you shim the cap mating faces an equal amount to allow them to seat fully without crushing the bearings, since now you have made then "longer"?
 
In the old days a machinist would get a pair of aviator snips-the kind with compound leverage- and take them apart and hone the cutting edges till they could shave paper. These were only used for brass shim stock and could cut a clean edge. I've gut up to .007 with the ones my grandfather had.
 
20 years ago in another life/job I used to fit white metal bearings regularly. Mainly condensate pump and motor bearings etc (the motors ran external whitemetal bearings rather than races), Most of them were about 8'' long X 3" to 4"dia.
If it's done correctly there shouldn't be any shims between the two halves when the bearing is in service. If it needs shims to prevent a nip then the bearing is not fitted correctly. (at least thats the way I was taught by the old fitters when I was an apprentice) The only time we used shims was when taking clearance readings. we'd shim between the bearing shells (the same as the pics here) lay some lead wire along the top of the journal and bolt the cap down. then remove cap, measure the thickness of the lead wire (with mics) where it had been crushed, subtract the thickness of the shim and that would be your clearance. (never had a lot of success using plastigage back then, though some blokes love it) If the clearance was not enough then you'd scrape some metal out of the top bearing half and repeat the process. If there was too much clearance then you'd have to take a bit off the face of bearing (where the to halves meet). If it was my machine I'd be scraping the bearings in correctly, but having said that I used to do it for a living. I can understand that for someone who has maybe not had training or experience in scraping bearings that the idea of doing that could be a bit daunting.
Having said all that, if the machine has been running ok with shims, why ruin a good relationship? LOL. If you decide to continue using shims it's best to use a minimum number. ie as thick as you can to do the job. Less chance of one moving on assemblyand less chance of an accumulated error creeping in.
hope this helps
bollie7
 
Mayhem link=topic=2112.msg13782#msg13782 date=1305113733 said:
Bollie7 - not heading over to Perth any time soon are you? I'll put on a BBQ and beer ;D To be honest, I wouldn't even know where to begin scraping a bearing and would more than likely end up wrecking it. As you said, it has obviously been working previously with the current shim set up and I can vouch for this given the amount of chips (swarf to you and I) that I dug out of her when cleaning her up. Everything I have found out to date points to a build date of between 1895 and 1905, so this may have been state of the art in bearings back then :eek: Going as thick as possible with the shims to reduce the overall number is the plan, as is to have equal thicknesses on each side.
Click to expand...
No, though I have been over once in the past and another life. I didn't realise you were in WA until now.
To be honest I think I would have to read up a little bit before I tackled scrapping a bearing again as its been more than 20 years since I last did one. I reckon you would be right about the bearing being state of the art for the time, the design can't have been too bad, what with it still going 100 years later. Actually I'm sure ball and roller bearings would have been fairly common back then but the plain bearings in the lathe make more sense for the time as they would have been a lot easier to maintain and repair with the commonly available tools at the time. Just about any corner blacksmith would have been able to re-metal white metal bearings. I am constantly amazed as to what was produced back then with the technology they had.
regards
bollie7
 
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