Reconditioning a PLA-CHECK

[Mfg_Engineer]

Does anyone know of a company that re-conditions this Cadillac gage? I found it in our company store room and would love to have it as a back up in another part of the shop, but it’s unusable in this condition.

 

[TGTool]

What makes it unusable? No electronics to fail, minimal wear on the disks, graduations look readable.

 

[sfriedberg]

What makes it unusable?

Rusty gaging surfaces.
Given the specs these things are intended to meet, this is probably impractical to recondition. You'd have to get the rust off, then build up the surfaces again with chrome plating (or similar) then precision grind and lap the gaging surfaces. It would be cheaper to buy a new one (even at the wallet swinging asking price). And infinitely more effective in the long run to cut the hands off the monkeys running the toolroom who allowed it to get that way.

 

[TGTool]

I've got a rusty one too. I think it was on a pallet of surplus set in the great outdoors for a while. (Aside: There ought to be a special place in hell for people to treat expensive, special equipment that way.)

Anyway, I've never seriously considered that this thing is salvageable, but I have wondered about their construction. From a fabrication perspective it would be much more economical to build up the column rather than making it one piece. With a one piece column a single mistake anywhere scraps the whole thing. As a built up assembly, the rings could be made and verified for thickness, then the intermediate pieces also selected and then verify that there are no tolerance stackups when assembled. I don't know if they do it that way, but one day I'll take after this one and find out.

 

[sfriedberg]

I think they do make some of them from stacked blocks, and it does seem like a lower-risk approach to manufacture.

 

[Bakafish]

I think they do make some of them from stacked blocks, and it does seem like a lower-risk approach to manufacture.

Looking at it, it would seem that this is also a stack, by making them round they can mount the stack directly to the fine adjustment screw, which is clever. The Mitutoyo design puts the stack on a carriage. I could see taking the stack apart and replacing or "lapping and shimming" the measurement disks. Corrosion between the spacers and the disks is less likely due to the tight fit, so the spacers are likely still in good shape. If you sacrifice the bottom surface accuracy as the part will become thinner, the top could be lapped clean and the amount removed shimmed with precision bearing shims. May be worth a try...

 

[Mfg_Engineer]

Thanks for the feedback. it will be of heavy heart to scrap this gage.

 

[TGTool]

If the issue is rust on the precision surfaces, you might do a thorough analysis to see if modest measures might make it modestly usable. If rust is only sporadic on the surface you may be able to recondition them and use the thing if you use it thoughtfully. Untreated rust has larger molecules than the original iron so will always be a raised surface. (Witness corrosion jacking in reinforced concrete) So in your case, you might be able to scrape off rusty areas without removing appreciable metal in good adjacent surfaces. Then in use, you'd just have to be sure your indicator point is finding an unblemished area somewhere on the relevant ring and do your reading. In my experience, the indicator is used as only a "null device". zeroing on the feature of interest, then bringing it to the gauge to again zero and read the actual dimension off the gauge. So you can wave the indicator around a bit on the nearest ring, or in the worst case gauge a little up or down and add or subtract the new number or the indicator.

 

[Homeshopblob]

If the issue is rust on the precision surfaces, you might do a thorough analysis to see if modest measures might make it modestly usable. If rust is only sporadic on the surface you may be able to recondition them and use the thing if you use it thoughtfully. Untreated rust has larger molecules than the original iron so will always be a raised surface. (Witness corrosion jacking in reinforced concrete) So in your case, you might be able to scrape off rusty areas without removing appreciable metal in good adjacent surfaces. Then in use, you'd just have to be sure your indicator point is finding an unblemished area somewhere on the relevant ring and do your reading. In my experience, the indicator is used as only a "null device". zeroing on the feature of interest, then bringing it to the gauge to again zero and read the actual dimension off the gauge. So you can wave the indicator around a bit on the nearest ring, or in the worst case gauge a little up or down and add or subtract the new number or the indicator.

+1 for this, if you want to use it on the shop floor and not in a metrology lab. I redid a B&S Hite-Icator. I found the column was assembled of gage block quality parts that needed to be wrung together in order to not have a cumulative error as they were assembled.

If I were faced with that gage, I'd remove that column and derust it in Evapo-Rust without further disassembly and inspect it. I'd then reassemble it in the body of the gage and spend some time comparing it to stacked gage blocks. I'd expect it to be useable to a few tenths error at most, if not better. DON'T scrape the lapped surfaces.

I really doubt you'll find a gage lab willing to work on it.

 

[ballen]

I like Evaporust a lot, but don't use it on ground/lapped/precision surfaces, because it etches them. My suggestion would be electrolytic rust removal in a caustic solution. That will remove (reduce) the rust without damaging the precision surfaces.

 

[michiganbuck]

OT:
Cadillac gauge is no longer in its old Warren Mi, Groesbeck building. Looks like a new name on the shop, but I think it is another high tec outfit.

 

[TGTool]

IIRC there are ceramic "stones" intended for dressing gauge blocks without appreciable abrasive action that ought to deal with high spots but leave good surfaces still pretty original. A modest refurb without complete disassembly would be a BUNCH easier. (is that a valid measure of effort?)

 

[jccaclimber]

1. That's a tragedy. We already know that, but I have to say it.
2. As stated above, the rusty areas are like low, but anything still clean is probably useable. I'd say this sort of "It's ok in places" use is ok for an environment that doesn't require a lot of customer certifications/traceability and uses a skilled operator, less so as those assumptions fail.
3. I bought a 12" Mitutoyo height master in visually spotless condition here in expensive leftcoastifornia at auction last year. It was a bit over $300 after all of the auction fees. I have a hard time seeing this one professionally repaired, or parts purchased for less than that.
4. A flat ground stone, particularly if its' fine grit and in a skilled hand can deburr a gage block. I wouldn't expect to take off more than a couple hundred nm, and that's with effort. The greater risk is minor scratches if you have a mirror finish currently. I suspect this is very similar to the proper stones officially sold for gage block care, though I've never handled one of those.

 

[Bakafish]

I have several of the Mitutoyo Cerastone gauge block deburring stones and they are great for removing invisible to the eye burrs, I doubt they will be effective on that corrosion though, they are just too smooth I think. Precision bench stones seem to have a little better bite, but I fear you would be doing more damage than good. If you can't relap the whole surface, better to just leave the corrosion damage in place and avoid it when referencing. The disk shape and being able to rotate them with the fine adjust, should still give you some life out of it if used carefully.

 

[4GSR]

I've had very good luck salvaging some square gage blocks that had spots of rust on them. Used a Norton very fine India stone to stone the rust spots down. It will stop cutting when it hits the harden surface of the gage block. Understand, you only use very gentile hand pressure and stroke the stone in one direction only. Next, take a Hard Arkansas translucent or ceramic stone and gently go over the surface to clean up what the India stone did not clean up. Do all of this dry. My gage blocks will never be a "A" grade ever, but for shop grade floor blocks they are fine for that. My "A" grade blocks stay in the gage lab, my office! Ken

 

[SynViks]

If the whole unit cannot be salvaged I'd suggest removing the micrometer on the top as that could be useful in some custom setups.

 

[gbent]

My first step would be to carefully scrape off the rust with a utility knife blade. They aren't hard enough to hurt the gauging surfaces. But if you need it calibrated because you are a ISO certified shop, it isn't going to happen.

 

[johnoder]

Be happy to pay packing / shipping just to HAVE IT - its all we had fifty odd years back during the apprenticeship at P&WA - and it doesn't have to pretend its "good".

 

[J_R_Thiele]

Its hard to judge the extent of rust in a picture, and my impression is that not all materials rust in the same way (diameter and depth of pits vs. flakes, etc). It may not be as bad as it looks

I would go with Evapo-Rust and a fine brass brush.

I Have not seen Evapo-Rust etching metal other than a part being partially submerged and left that way- when a stain area forms along the air fluid interface. Either fully submerge or use a surface application with frequent swabbing of fresh solution and use of the brass brush. If at all possible heat it before you work on it. The Evapo-Rust will work better and faster - and it will dry much faster after a rinse with distilled water. Oiling is the next step- and it will flow better on a warm surface also.

After it is cleaned some time with a indicator will give an idea if it is worth trying for certification.

 

[4GSR]

I had an awfully bad result using Evapo-Rust on some gage blocks when I tried it. It turned them "black" like a Parkerizing or phosphate coating left behind after cleaning them from the bath. And I wouldn't recommend electrolysis either.