Members algroves Posted July 1, 2006 Members Share Posted July 1, 2006 I bought a bicycle frame over the weekend that had a stress crack on the downtube, just behind a gusset where the headtube joins the downtube (in case you don't know your bikes, this is basically where the handlebars and forks meet the rest of the frame). The crack has been welded with a nice tidy weld across the crack by a scaffolding, but I'm wondering if its worth taking it to a welding shop and getting them to weld gussets across all the major stress points just to beef it up a little more. The frame is 7005 aluminum that has undergone heat-treatment when it was forged originally, but as far as I know it wasn't re-heat treated after the reweld. Would further gussetting across the reweld, and other known stress points, worsen the strength of the frame or improve it? I bought the frame very very cheap as I only intended to use it for about 6 weeks, but I really like the way it rides and I'd like to keep it going with confidence if possible. It's an off-road trials bike, which means it's used for jumping and hopping around on walls/rocks etc. I've heard of some rewelds lasting over a year, while others last less than a week. I've also heard that if you reweld one particular part of an aluminium frame, the stress will be re-directed to other parts - hence my gussetting idea Cheers, as always Al Link to comment Share on other sites More sharing options...
Members Pablito Posted July 1, 2006 Members Share Posted July 1, 2006 Rewelding an aluminium bike frame is usually not a great idea. And... it will not redirrect the stress. Aluminium welding is also tricky. Some folks are really great at it... But many are average to poor. YMMV pax Link to comment Share on other sites More sharing options...
Members Tonemeister87 Posted July 1, 2006 Members Share Posted July 1, 2006 Aluminium is for the weak Link to comment Share on other sites More sharing options...
Members drucifer Posted July 1, 2006 Members Share Posted July 1, 2006 Welding aluminum sucks. It'll never be as strong. Link to comment Share on other sites More sharing options...
Members elvis06 Posted July 1, 2006 Members Share Posted July 1, 2006 if it was rewelded after it was heat treated than it's garbage...... You now have a brittle joint that will only continue to break every time you try to fix it. heat changes the molecular structure of metal-not so much the heat that affects it as to how fast it cools. When they heat treat it they heat it up to a certain temp and than dip it into oil to cool it off rapidly..what this does is take a (malleable) or soft piece of metal and harden it so it will become more rigid, but at the same time more brittle. Kinda the opposite of annealing. Take it to a shop that deals with aluminum and get their advice. like the other dude said there are few out there who weld aluminum well-one good reason is the welding fumes given off from aluminum are toxic. Link to comment Share on other sites More sharing options...
Members Rik-Guitarstudi Posted July 1, 2006 Members Share Posted July 1, 2006 I was thinking you could get away with the way it was.. but, after more thought.. I would get another frame. Sounds like the guy before you jammed it up pretty hard. The major cause of failure with aluminum is fatigue caused by overflexing, (surely they heat treated/aged it from factory!) so there will be other places likely to have cracks you may not see, (inside). if the bottom tube flexed and cracked, something else flexed too. making more repairs may make it worse. I would Replace the frame. Link to comment Share on other sites More sharing options...
Members algroves Posted July 1, 2006 Author Members Share Posted July 1, 2006 It wasn't actually a crash that did it - the guy was practising a move called hooking, where you hook your front wheel over a ledge and use it to pull yourself up. Other than that the frame is in good condition, and has been looked after. If I were to send the frame off to be heat-treated again, would this return the former strength of the frame? Cheers Al Link to comment Share on other sites More sharing options...
Members algroves Posted July 1, 2006 Author Members Share Posted July 1, 2006 Al Link to comment Share on other sites More sharing options...
Members harry manback Posted July 1, 2006 Members Share Posted July 1, 2006 typically, welding aluminum after it's been heat-treated will only result in further cracking. it gets very brittle at the re-welded joint, and you can't do much about it. you could try to find a good machine shop and see if they can put heater blankets on the entire frame, and then weld it, and then let it cool down. that's one way to do it, but that just helps the weld in being not quite so brittle. just a suggestion. good luck, with whatever avenue you take. jeff Link to comment Share on other sites More sharing options...
Members redeva Posted July 1, 2006 Members Share Posted July 1, 2006 ^^^^ Pretty much got it nailed. Is it worth it?It would probably work out cheaper/more efficient to pick up a new frame. But I'm not much on bikes. Link to comment Share on other sites More sharing options...
Members FrankLee11 Posted October 2, 2017 Members Share Posted October 2, 2017 I'm a long way from being a specialist welder. I have completed some aluminum work yet it is considerably solid to weld than harden as it is anything but difficult to squall up with openings in the work. Link to comment Share on other sites More sharing options...
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