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Question, what tolerance for a interference fit

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  • #16
    I was referring to the OD sizing and finish on the sleeve and ID of the casting to aid with a good bond. For the ID of the sleeve you'd want to copy the original specs for clearance and surface finish of course. But then I'm guessing that part is aimed towards Mikey's post....
    Chilliwack BC, Canada

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    • #17
      Looking at brass tube specs the size of the ID can vary a lot and can be out of round as well. I was thinking you are going to bore the ID, but it looks like I made a wrong assumption. Honing can put the bore ID to size if you have some material to play with, so you have a real hone and a honing machine? You did not say anything about it...

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      • #18
        I would suggest you get the brass tubing first, measure it and then decide if it is usable for what you want to do.

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        • #19
          When I do fits like this I use a heat gun to get the aluminum up around 350f. Checking it with a laser temp indicator.
          Nowadays you could probably put it in an air fryer for a few minutes.
          I chill the other part in an Acetone/Dry Ice mix which allows you to take almost full advantage of the -109f dry ice temp when immersed in the Acetone.
          The dry ice weathers off and the Acetone is fully re-usable for whatever.
          For what you want to do, I’d go .0006-.0008. It’s not rotating and you don’t want to stress or crack the casting.
          Illigitimi non Carborundum 😎
          9X49 Birmingham Mill, Reid Model 2C Grinder, 13x40 ENCO GH Lathe, 6X18 Craftsman lathe, Sherline CNC mill, Eastwood TIG200 AC/DC and lots of stuff from 30+ years in the trade and 15.5 in refinery unit operations. Now retired. El Paso, TX

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          • #20
            I completely agree with BCRider -- I wouldn't use red loctite, but rather something from the 600 series like 641, 648 or the aforementioned 680 which is specifically formulated for cylindrical press fits by the manufacturer. Read the data sheet and add the clearance so you don't squeegee all the goop off the shaft with a zero clearance fit.

            That is, if I were to use loctite. My first choice will always be a proper thermal shrink fit. You have a ceiling to which the hole part (aluminum) can go before it degrades, so you will need to cool the mating part as well. I have used LN2 and CO2 to shrink steel parts to go into aluminum housings. Brass is about 1.8-2x the alpha of steel, so you can get some decent shrink on the part in conjunction with going to 300-350F on the aluminum without any real risk of compromising the aluminum.

            L' = L * (1 + a * dt)

            Aluminum, a = 25.5 ppm
            0.75 * (1 + 25.5E-6 * (150 - 21)) = .7525 [150C = 300F]

            Brass, a = ~18.9 ppm
            0.751 * (1 + 18.9E-6 * (-50 - 21) = .7499 [-50C is about where liquid CO2 runs, shoot it from a bottle with a siphon valve or invert it and wash the part until it frosts up]

            (hole .7525) - (shaft .7499) = .0026 in of positive clearance, which should drop in but will lock up with a thou of nominal shrink at room temp.



            alpha values and formulae gotten from here: https://www.sciencedirect.com/topics...t-of-expansion
            -paul

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            • #21
              Loctite is not anaerobic per se. It is actually catalyzed by metal ions which causes it to harden. I used some Loctite pipe sealant on an RO project and couldn't get it to seal, got leaks everywhere. Talked to Henkel and found out that the jobsite temperature was below the long term storage temperature for the product!

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              • #22
                If I was doing that job, I'd probably use a Loctite product. That said, a trick I use if doing a shrink-fit assembly is to set my telescoping gauge to the size I want the "outside" part to be, then use it to check while heating the part. IE: I'd probably want to expand the wheel cylinder to .002 or .003 larger than the OD of the tubing/liner, and using the telescoping gauge makes it easy.

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                • #23
                  Gary, are you still talking about the thread compounds? The data sheet for the 680 adhesive that I linked to in a previous reply stated that it is an anaerobic adhesive.
                  Chilliwack BC, Canada

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                  • #24
                    Didn't see what car this is for, Is this Drum or Disk Brakes. For either the 2 biggest concerns would be strength and leakage. And I would suggest a Stainless sleeve as it would be more corrosion resistant. In either type brake cylinder the forces involved would not tend to force the sleeve to move, actually with the drum brakes the net force on the sleeve would be zero as the pistons would be pushing opposite each other and none of the forces would make the sleeve slide, and any expansion of the sleeve under pressure would make it tighter.

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                    • #25
                      Some more great suggestions, I appreciate them all.. Kf2qd This is a single cylinder rear wheel drum brake setup. The car is a Morris Minor Traveller that I recently acquired and apparently needed a brake service that I'm now doing. To keep from having the same problem (corrosion and system failure) in the future, sleeving the cylinders is what I'm doing. I have another post about machine setup and what to do to machine the cylinder.

                      The Holiday will keep me away from the shop until next week, but I do have the week off, so hopefully I get time in the shop and will post the results when I get a chance. Thanks for all the advice and help guys...!

                      TX
                      Mr fixit for the family
                      Chris

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                      • #26
                        Originally posted by Mr Fixit View Post
                        Some more great suggestions, I appreciate them all.. Kf2qd This is a single cylinder rear wheel drum brake setup. The car is a Morris Minor Traveller that I recently acquired and apparently needed a brake service that I'm now doing. To keep from having the same problem (corrosion and system failure) in the future, sleeving the cylinders is what I'm doing. I have another post about machine setup and what to do to machine the cylinder.

                        The Holiday will keep me away from the shop until next week, but I do have the week off, so hopefully I get time in the shop and will post the results when I get a chance. Thanks for all the advice and help guys...!

                        TX
                        Mr fixit for the family
                        Chris
                        I think you are doing a great job, keep it up. aaJR

                        P.S.> This!! Its a good fix in my opinion. Fixit= "(corrosion and system failure) in the future, sleeving the cylinders is what I'm doing."

                        You should have put a provisional patent up. Its a good fix. JR
                        Last edited by JRouche; 12-25-2021, 03:34 AM.

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                        • #27
                          Hi JR,

                          Thank you for the nice comment and support. I'll report back after the XMas weekend when I get back into the shop..

                          TX
                          Mr fixit for the family
                          Chris

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