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#1
03-19-2024, 05:35 PM
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Propane to fix cracked rack?
First, shoutout to Tubus and JBI Bike for the warranty replacement of my Tubus rack.
I got to keep the old rack and would like to try my hand at welding/brazing it back together. Would a simple propane torch hooked up to my bbq propane tank and some Stay-Silv 15 be sufficient for fixing this? 
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#2
03-19-2024, 05:37 PM
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Is the rack steel or aluminum?
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#3
03-19-2024, 06:04 PM
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steel
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#4
03-19-2024, 07:29 PM
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I claim no expertise, but I've messed around quite enough with DIY bike related brazing fixes to know enough to be foolhardy including a couple of frames that were built up, later cut up to avoid potential catastrophe. IMHO, no. Propane without O2 will not get hot enough, or at least not heat fast enough to seriously anneal and weaken the joint, and using silver would be tricky, it's used to fill capillary spaces not rack joints. At the very least you need MAP gas and a bronze rod (and flux of course), but even then, you would be annealing the tubing quite a lot, if it broke once it will likely break again in the same place, where do you want to be when that happens? I'd take it to a good welding shop and have a pro do it if you want any confidence in the fix.
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#6
03-20-2024, 07:39 AM
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From the picture, it looks like the tubing is cracked at the root of the tig weld. If that is correct, then your option for a low load repair is either a big brass fillet bridging the crack and tying into the tubing and the intact weld or a tig weld repair.
15% doesn't have enough strength to work in a fillet situation, it does "wick" into joints nicely though. 45% would be a slightly better option but brass would be better than both of them. I use lots of 15% and 45% in my day job and only occasionally brass. Use an oxy-acetelene rig for all 3 so you can direct the heat to get penetration and build a fillet afterwards. If you have a buddy with a tig then ignore the above and have him weld it. 
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#8
03-20-2024, 07:49 AM
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Quote:
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#9
03-20-2024, 09:46 AM
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Quote:
__________________
Marc Sasso A part of the resin revolution!
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#10
03-20-2024, 09:51 AM
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I'm going to vote for carbon fiber and fiberglass here. Sand off the area around the joint, add some epoxy to fill the crack, wrap the joint with fiberglass, wrap again with carbon fiber. You don't actually have to to a good job and it'll be more than strong enough for this application.
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Instagram - DannAdore Bicycles
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#11
03-20-2024, 09:52 AM
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Quote:
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#12
03-20-2024, 09:53 AM
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I'd strip to steel, brush flux, wrap steel wire around in figure 8s and lay some brass over it. Not sure propane will be enough heat though??
J-B Weld work great until you actually load it be my guess.
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This foot tastes terrible! 
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#13
03-20-2024, 09:53 AM
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Quote:
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#14
03-20-2024, 10:00 AM
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Anyone who is missing that just JB weld isn't gunna just crack same place again... Well, that's how my minds eye sees it anyway.
Now if you striped, laid thin JB and figure 8 wrapped some fiber, heck dental floss even and laid more JB over, it might surprise as a viable repair and not crack again 1st loaded ride. 4th probably. 
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This foot tastes terrible!
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#15
03-20-2024, 10:03 AM
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Quote:
J-B Weld™ has a tensile strength of 5,020 PSI Tensile strength of steel typically spans between 36,000–50,000 psi The tensile strength of TIG butt welds reaches to 97 % of the base metal ultimate tensile strength. Yea, OK!
__________________
Marc Sasso A part of the resin revolution! Last edited by m_sasso; 03-20-2024 at 10:08 AM.
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