3M DP420 (Epoxy for a bottom bracket)- Mtbr.com
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  1. #1
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    3M DP420 (Epoxy for a bottom bracket)

    Hello,

    I've got a frame with a press fit bottom bracket. Long story short, the bottom bracket shell ultimately got trashed and I replaced the frame.

    On the replacement frame I began to get some noise from the PF BB and started to think about trying to epoxy one in. Realizing that I have a second frame I decided to try it.

    I honed out the shell to get a good bond line (.008") and selected 3M DP420NS for it's very high shear properties. However, I don't have the ability to etch my substrates so I just sandblasted both the shell and my BB cups before gluing them. I used a thread together Wheels Mfg. bottom bracket hoping that that would help to carry some of the load.

    After 24 hours I tried turning the cups with a BB wrench and both felt solid. Now that I have the frame built up, I'm hoping it will be a permanent fix (bearings are removable so if the cups never move again I'll be a happy camper).

    I know how hard bonding aluminum can be though. Has anyone had any experience with this stuff?

    Thanks.

  2. #2
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    Your method and approach are well thought out. The only thing I will add, is that did you do a test first? That is, blasted a piece of aluminium, then put a blob of 3M on the Aluminium and left to cure. Then tried to remove the blob. If it fell off, obviously, progress no further. If it sticks and holds on well, you have a contender.

    Now that you have done the bonding, give it a go, only real way to find out.

    Eric
    If I don't make an attempt, how will I know if it will work?

  3. #3
    will rant for food
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    That glue is @#$*ING BONKERS. Use it to your heart's content.

    I have it doing a silly task of helping lift up a mill spindle that is way too heavy for the CNC chassis that it resides within. It's essentially a small plate glued to the bottom of the Z axis gantry, and I mounted some air springs to the plate. So, this particular bond is working in the "peel strength" mode, which I've gathered is poorly understood compared to shear strength. Even so, the bond remains.

    Since you know about the bond line, you've covered one of the more important details. The stuff doesn't work worth beans if the bond line is too razor thin.
    Disclaimer: I run Regular Cycles (as of 2016). As a profiteer of the bicycle industry, I am not to be taken very seriously.

  4. #4
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    Ironically, I actually realized that I did my math wrong. I have a .008" difference between the cup and my shell, but concentrically that only equates to a .004" bond line. That said, I do think there was some taper to the shell and I measured at the middle of the bonding surface. It didn't feel excessively tight with the .007" spacer beads that I used and there wasn't an excessive amount being scraped off that I noticed. 3M claims a 3-5 mil bond is ideal for shear anyways.

    I did some lap shears today using a .005" bond line and a heat accelerated cure and was still getting shears in the low 2000's which I'm happy with considering I'm not able to etch.

    Thanks for the info guys. I was mostly looking for some first hand experience.
    Last edited by Shinkers; 02-05-2018 at 08:01 PM.

  5. #5
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    In respect to first hand experience, it is likely that in this community that no-one has done this specifically, so we will await the report from your trial so we can add this to our problem solver list.

    Always good to find a leader in a new experiment...

    Cheers
    Eric
    If I don't make an attempt, how will I know if it will work?

  6. #6
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    Sorry, I know that no one has done this specific thing, but I figured someone had used DP420 for something. I'm glad to hear that Drew has some experience with it and has been successful.

    I'll get a ride on it this weekend. Should be interesting...

  7. #7
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    So far I've managed to get two rides on this thing. So far, so good (though I'm probably jinxed now).

    On Saturday I did have a pretty gnarly off camber landing from about a 3 foot step down that I think was about as much abuse as the bond will see. The frame got side-loaded pretty hard along with compression of landing the jump.

    Fingers crossed that this is a permanent fix.

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