How to unstick center disk of round slide rule?

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To a certain extent that depends on how you use it.

As I already stated. Dry mold release lube in a spray can. Food grade is the least cumulative.

Forget my suggestion to iron the plastic part flat. With that insert, you can't flatten it out properly and you'll just cause more problems.

Took the calipers to it:

The aluminum base is 0.022" thick, the recess for the center disk (and thus the thickness of the outer plastic ring) is 0.051", the rotating inner disk is 0.040" thick so has some wiggle room for an underlayment. Even up to 0.018" (minus some clearance) because the brass center hub sticks out 0.058" above the aluminum surface.

Professor Hamann has responded and for the warped disk he suggested clamping it between two good sized aluminum plates and then immerse in hot water. He seems to be quite the expert on slide rules restoration.

That might work. But you'll probably need to cut one out to fit your center bushing. And I'd go a step further and machine a stud into one plate to ensure that the disc cools with the bushing C/L held at right angles.

But its good to hear that my 'heat it up' technique isn't totally bogus.

It's just the center disk that's bulging up in the middle, the rest of the slide rule is straight.

So the periphery of that disk is dragging on the alumin(i)um part? Flattening it out might help, but that's going to be tricky with the center bushing. A thin washer that fits around the smaller diameter hub and lifts the center disk a few thousandths might help. And if you can find some Teflon stick on 'dots', you can put a few of these around the outer parts of the recess to keep the plastic disk from contacting the aluminum when you push it around.

You'd have to use the teflon because the center wheel is sorta floppy. The only way to move it is to press down on it with your thumbs.

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Thank you, a 0.003" PTFE (or maybe the right variation of PET (nylon) or=20 polyethylene) washer will work wonders. Especially if assisted by = silicone=20 lubricant film applied to the aluminum as liquid or spray. Now if i just= =20 knew where to get it, try TAP plastics though.

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Yep, have to get to a TAP outlet soon.