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  1. #1
    Senior Member ljsense's Avatar
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    Gluing shift bosses to the downtube instead of brazing them

    Not the reasons why brazing on would be better. That's pretty obvious.

    My question is, would JB Weld or some similar epoxy be strong enough to hold shift bosses to the downtube?

    It would help me out a bunch if this solution works:

    1. Don't have to buy a brazing rig
    2. Only lose the paint where it's necessary to glue, not the whole brazing area
    3. Low stakes in terms of safety
    4. Bosses are $20, let me use a 7400 group with 6-speed shifters

    Thanks for your experiences with epoxy

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    Clamp on down tube shifters were pretty common 30 years ago. If you live near a bike co-op hit their parts bin for a set, or check out ebay:
    downtube shifter clamp | eBay

  3. #3
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    Quote Originally Posted by John Nolan View Post
    Clamp on down tube shifters were pretty common 30 years ago. If you live near a bike co-op hit their parts bin for a set, or check out ebay:
    downtube shifter clamp | eBay
    But those frames usually had a nub on the downtube to prevent the clamp from slipping.

  4. #4
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    Quote Originally Posted by ljsense View Post
    My question is, would JB Weld or some similar epoxy be strong enough to hold shift bosses to the downtube?
    (...) Thanks for your experiences with epoxy
    Even with proper surface prep (roughing up the surface of the downtube), I don't think epoxides will be able to handle the repetitive mechanical stresses (shearing) of shifting.

    Epoxies are great for bonding when the force is normal (perpendicular) to the bond (tensile) as it spreads the force over the bond area. In your case, the cable pulls the DT shifter to the side (parallel to the bond - shear).

    It may work for a time, but it will not hold for long. YMMV.

  5. #5
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    Quote Originally Posted by Bezalel View Post
    But those frames usually had a nub on the downtube to prevent the clamp from slipping.
    My steel frame doesn't have nubs. The DT shifter is held by the clamp pressure.

  6. #6
    SE Wis dedhed's Avatar
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    '68 Raleigh Sprite, '02 Raleigh C500, '84 Raleigh Gran Prix, '91 Trek 400

  7. #7
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    Quote Originally Posted by dedhed View Post
    +1

  8. #8
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    You can silver braze those in place with a simple plumbers propane torch. The biggest expense will likely by the 45% silver. Of course, the paint will be toast for several inches above and below the bosses.

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    Quote Originally Posted by randomgear View Post
    You can silver braze those in place with a simple plumbers propane torch. The biggest expense will likely by the 45% silver. Of course, the paint will be toast for several inches above and below the bosses.
    The OP has already expressed his intent not to do the things you mentioned.

    Quote Originally Posted by ljsense View Post
    1. Don't have to buy a brazing rig
    2. Only lose the paint where it's necessary to glue, not the whole brazing area
    3. Low stakes in terms of safety
    (...)

  10. #10
    Senior Member ljsense's Avatar
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    Are you saying that some form of plumber's or electrical solder would be strong enough?

    I thought that hard silver solder was like brass solder and requires what I've always heard called a "brazing torch" -- that is, a much hotter oxy-acetylene rig.

    I don't know the metal content of the soft solder that uses the plumber's torch you describe -- the little blue propane jobs with the threaded brass adjustable flame.

    Anyway, anyone know if any kind of solder that can be melted with a propane torch would be strong enough? I might go for plumber's soldering if that's viable -- I already have a plumber's torch and soldering wire.

    e_guevara's points about epoxy and shear forces are good ones.

    As for the other advice, thanks, but I already have a pair of clamp on shifters. They're old Campy friction levers. What I really want to use, though, are these sweet Dura Ace 6-speed indexed shifters that go with everything else. They have the round silver scalloped bases that want to mate beautifully with a downtube and bosses, not get cobbled on top of some clamp-on aftermarket thing.

  11. #11
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    Silver braze is a relatively low melting alloy that is much stronger than any "soft" (Pb/Sn type) solder. It can be used with a propane or better, a Mapp gas, torch. As noted, epoxy won't be strong enough and brazing in one form or another will be needed if a clamp-on style isn't acceptable.

  12. #12
    Old fart JohnDThompson's Avatar
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    Non-ferrous frames use epoxy to hold lever bosses, but usually have a rod extending through the down tube to hold the bosses in place against the shear forces. This might be your best solution if you're committed to using the Shimano levers with the proprietary base plates. Otherwise, a clamp-on lever set is a quick and effective solution, even if the frame lacks a stop to prevent the band from sliding. You just need to tighten the clamp sufficiently to prevent this from happening.

  13. #13
    You Know!? For Kids! jsharr's Avatar
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    I am not sure of the process used, but my first, okay second, you got me, serious road bike was a 1988 Trek 1000. It was bonded Aluminum and shifter bosses were bonded on as well, but as JohnDThompson mentions, there was a rod through the frame connecting the bosses.

    I managed to shear one off in a silly way, trying to undo my toes straps w back in the strap and cleat days while still sitting on the bike by supporting myself against a post in front of my apartment. Hand slipped off post and I took a slow motion fall. Bike hit post and with my weight still attached, the shifter and boss sheared off.

    Trek fixed it under warranty. Been a loyal Trek customer ever since.
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    Quote Originally Posted by colorider View Post
    Phobias are for irrational fears. Fear of junk ripping badgers is perfectly rational. Those things are nasty.

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    Quote Originally Posted by JohnDThompson View Post
    Non-ferrous frames use epoxy to hold lever bosses, but usually have a rod extending through the down tube to hold the bosses in place against the shear forces.
    Yes, my son-in-law's Trek-built late '90's Klein had the shift bosses held on with double-face tape and a threaded rod across the downtube that was screwed into both bosses from the inside. The real strength was provided by this rod. However the threads were a bit fragile and could strip if abused. Trek/Klein provided a lot of replacement bosses and rod kits and I still have one in my parts box.

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    Senior Member Kopsis's Avatar
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    The best two-part structural epoxies (stuff like 3M DP420) can get you up to 4500 psi shear strength with proper surface prep and optimal curing. On a half inch shifter boss that means a theoretical max ability to withstand about a thousand pounds of shear force. Realistically you'll only achieve 25 - 50% of that, so 250 to 500 lb. That's actually in the ballpark where it might work. I'd be tempted to try it. If it doesn't work, it's unlikely to be catastrophic and you can always fall back to one of the other options.

  16. #16
    You Know!? For Kids! jsharr's Avatar
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    Quote Originally Posted by colorider View Post
    Phobias are for irrational fears. Fear of junk ripping badgers is perfectly rational. Those things are nasty.

  17. #17
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    Short answer to the original question. As of now, there is no glue or bond material strong enough for this task. If a perfect match of the curvature could be made, a superglue type product would be strongest. But the repeated dynamics (juggling) from shifting would also cause that to fail.
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  18. #18
    Nigel nfmisso's Avatar
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    Quote Originally Posted by Kopsis View Post
    The best two-part structural epoxies (stuff like 3M DP420) .......
    And 3M DP460. They both should be cured at room temperature for 24 hours then heated to at least 140°F (60°C) for a couple hours for full strength. Either costs about $25- for a 1¼ ounce cartridge, which requires the use of $90- *** and ideally a static mixing nozzle $25/dozen.

    The surfaces must be very clean (wipe down with 91% Isopropyl Alcohol 5 minutes before applying the epoxy, and as noted roughened.

    Regarding brazing - a small butane torch can be had for less than $50- including fuel, and will reach 2500°F and provide enough heat to do the job. This is hot enough to effect the heat treatment of the steel - be careful.

    Source of all the prices listed above: McMaster-Carr You can often find things for less at other places.
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  19. #19
    coprolite fietsbob's Avatar
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    A larger surface area than the typical shifter boss offers may, function ..

    but using a band mounted shifter set is much simpler ..

    you can epoxy it on and the band clamp will be a good clamp while the epoxy is curing, If you wish.

  20. #20
    Nigel nfmisso's Avatar
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    Quote Originally Posted by FBinNY View Post
    Short answer to the original question. As of now, there is no glue or bond material strong enough for this task. If a perfect match of the curvature could be made, a superglue type product would be strongest. But the repeated dynamics (juggling) from shifting would also cause that to fail.
    NOT. Cyanoacrylates are fast bonding, but not suited to structural applications. Often for structural applications, a super glue will be used for fixturing while the structural epoxy is curing. super glues are brittle, and the high impact ones are not strong.
    Nigel
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  21. #21
    Member 401flava's Avatar
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    Quote Originally Posted by Kopsis View Post
    The best two-part structural epoxies (stuff like 3M DP420) can get you up to 4500 psi shear strength with proper surface prep and optimal curing. On a half inch shifter boss that means a theoretical max ability to withstand about a thousand pounds of shear force. Realistically you'll only achieve 25 - 50% of that, so 250 to 500 lb. That's actually in the ballpark where it might work. I'd be tempted to try it. If it doesn't work, it's unlikely to be catastrophic and you can always fall back to one of the other options.
    amen. Makes sense to me. C'mon, seriously he's not going to change gears with a crowbar and a 20lb sledgehammer. Granted its not ideal, you're using a (short) lever to apply force every time you shift, but how much force? A good 2-part epoxy would hold, I'd bet forever. Now, I'd do everything I could to make it work...Correct me if I'm wrong, but I guess I'd rough it up ALOT, get some good groves in it to grab onto and then a solid clean up with some solvent. I'm thinking a wire brush Dremel bit would chew it up nice nice. If the frame is nothing special, I might even drill a tiny anchor hole or two to be a superhero,but that's likely overkill.

    That said, epoxying is going to be as permanent as anything else, so I'd probably at least explore a more conventional approach. I'm slightly confused about why clamp-on BOSSES won't work...the shifters you want to use won't know the difference. You don't have to buy inferior clamp on SHIFTERS,just a clamp on boss. What's the issue? There's a nice DA on ebay as we speak. There're a zillion out there, some are beautiful...old Campys and Shimanos were artsy little bits. There's no cobbling, the only difference would be that you see the band of the clamp. Same curved surface, same boss. Jeez, you could paint the band to match the DT and hardly see it at all.
    "Life is just a long,crazy bicycle ride..." -an infinitely wise Buddhist bicyclist

  22. #22
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by fietsbob View Post
    A larger surface area than the typical shifter boss offers may, function ..
    Yes, that's what Trek did in addition to using the rod through the down tube. And what was suggested here:

    1990 Trek 1000 Aluminum Downtube Shifter Broke Off/Broken. Options? Pics inside!

  23. #23
    Rhapsodic Laviathan
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    I have a nice fuji road frame with a broken rear drop out, that was "repaired" with jb weld. A two part epoxy is not going to hold dt shifters- which are always under tension, nomatter the gear. OP should just get clamp ons- it's even lesser work than he wants to do to begin with. Plus if something should happen to the frame, the whole transmission system can be moved to another frame.

    Compared to just gluing them on, brazing them on, or praying the skotch tape wont fail...

    Quote Originally Posted by 401flava View Post
    amen. Makes sense to me. C'mon, seriously he's not going to change gears with a crowbar and a 20lb sledgehammer. Granted its not ideal, you're using a (short) lever to apply force every time you shift, but how much force? A good 2-part epoxy would hold, I'd bet forever. Now, I'd do everything I could to make it work...Correct me if I'm wrong, but I guess I'd rough it up ALOT, get some good groves in it to grab onto and then a solid clean up with some solvent. I'm thinking a wire brush Dremel bit would chew it up nice nice. If the frame is nothing special, I might even drill a tiny anchor hole or two to be a superhero,but that's likely overkill.

    That said, epoxying is going to be as permanent as anything else, so I'd probably at least explore a more conventional approach. I'm slightly confused about why clamp-on BOSSES won't work...the shifters you want to use won't know the difference. You don't have to buy inferior clamp on SHIFTERS,just a clamp on boss. What's the issue? There's a nice DA on ebay as we speak. There're a zillion out there, some are beautiful...old Campys and Shimanos were artsy little bits. There's no cobbling, the only difference would be that you see the band of the clamp. Same curved surface, same boss. Jeez, you could paint the band to match the DT and hardly see it at all.
    The speed is break neck, faster than a high speed dual cassette tape deck.

  24. #24
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    Yeah, all those carbon frames with brazed on cable stops... because epoxy isn't strong enough.
    Dream. Dare. Do.

  25. #25
    Senior Member
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    Quote Originally Posted by Rowan View Post
    Yeah, all those carbon frames with brazed on cable stops... because epoxy isn't strong enough.
    On carbon, the stops are bonded onto the same resin that holds the CF together - one continuous structure.

    We're talking about using epoxy to bond dissimilar materials. It's not the structural strength of epoxy, it's the bond/adhesion of epoxy to metal.

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