Manus-Rider Posted August 7, 2011 Report Share Posted August 7, 2011 Hello, iam looking at the koxx silver sky that is for sale on this forum by rob. It says in the description "that it has a hairline crack behind the headtube were the two tubes meet near the cut out". if i got that welded how long would it probably last before it snaps? And iam not a very hard rider really i normally will just be doing sidehops and back wheel things and gaps I dont do hooks, but i do the Odd to front every now and again. Please help me Cheers charlie Quote Link to comment Share on other sites More sharing options...
old'scoolfool Posted August 7, 2011 Report Share Posted August 7, 2011 theres no science when it comes to cracks, could crack straight away could last ages place your chips 1 Quote Link to comment Share on other sites More sharing options...
Andeee Posted August 7, 2011 Report Share Posted August 7, 2011 How longs a piece of string? Quote Link to comment Share on other sites More sharing options...
Twitch-119 Posted August 7, 2011 Report Share Posted August 7, 2011 How longs a piece of string? Half it's length times two Quote Link to comment Share on other sites More sharing options...
SamKidney Posted August 7, 2011 Report Share Posted August 7, 2011 Mate of mine had his Koxx welded and it didn't last long at all, but then another guy has his welded and it lasts ages. All depends mate. If its been like that with the previous owner for a while, then It could be ok. Quote Link to comment Share on other sites More sharing options...
MonsieurMonkey Posted August 7, 2011 Report Share Posted August 7, 2011 Surely the quality of the weld is the most important thing to get the most out of it? Quote Link to comment Share on other sites More sharing options...
Manus-Rider Posted August 7, 2011 Author Report Share Posted August 7, 2011 thanks for all the reply's. and as MonsieurMonkey says it must depend on the quality of the weld aswell? Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted August 7, 2011 Report Share Posted August 7, 2011 Indeed, I wouldn't weld it, it would probably add more problems if done half assed, if it is made with that koxx material also you will have real problems welding it.Ask him how long he has been riding it with the crack and make a judgement from that. Ironically if he had left it painted it probably wouldn't have been noticed at all and may last for a long time un-noticed. Cracks are not always the death knell for frames, although round the headtube could be sketchy if it goes. Buy my Hydrox instead? Quote Link to comment Share on other sites More sharing options...
dave33 Posted August 10, 2011 Report Share Posted August 10, 2011 Indeed, I wouldn't weld it, it would probably add more problems if done half assed, if it is made with that koxx material also you will have real problems welding it.Ask him how long he has been riding it with the crack and make a judgement from that. Ironically if he had left it painted it probably wouldn't have been noticed at all and may last for a long time un-noticed. Cracks are not always the death knell for frames, although round the headtube could be sketchy if it goes. Buy my Hydrox instead? what are you on about? yes get it welded, if you take it to some one decent with a tig it will be ok. and as you said you dont do hooks then there is very little amounts of stress in that area. so it will last around 4-6 months but if you do start doing hooks it will be off in weeks. Quote Link to comment Share on other sites More sharing options...
wip-bikes Posted August 10, 2011 Report Share Posted August 10, 2011 It will be good as gold as long as you get it heat treated properly afterwards. Take it to a professional fabricator and they will be able to advise you Quote Link to comment Share on other sites More sharing options...
super Posted August 11, 2011 Report Share Posted August 11, 2011 It will be good as gold as long as you get it heat treated properly afterwards. Take it to a professional fabricator and they will be able to advise you What this man says is true but it will be expensive to get it heat treated. Best bet would be to ride it for a while and only get it welded if / when the crack starts to grow. You can score a couple of marks at each end of the crack to keep an eye on how fast it's growing. Quote Link to comment Share on other sites More sharing options...
Alex Dark Posted August 11, 2011 Report Share Posted August 11, 2011 I'm pretty sure you can't heat treat a re-weld....but someone a little more into metallurgy may be able to shed some more light on the matter Quote Link to comment Share on other sites More sharing options...
super Posted August 11, 2011 Report Share Posted August 11, 2011 Yes you can, but you'll have to find someone with an oven big enough! Quote Link to comment Share on other sites More sharing options...
JD™ Posted August 11, 2011 Report Share Posted August 11, 2011 Nah, it f**ks with the original heat treating as far as I'd heard? Quote Link to comment Share on other sites More sharing options...
dirt jumper jake Posted August 11, 2011 Report Share Posted August 11, 2011 I had a rockman maladie, that died. because it cracked, 3 times and i had it welded Quote Link to comment Share on other sites More sharing options...
Sam T Posted August 11, 2011 Report Share Posted August 11, 2011 I had a rockman maladie, that died. because it was a Rockman. That's better! Quote Link to comment Share on other sites More sharing options...
F.N.G Posted August 11, 2011 Report Share Posted August 11, 2011 (edited) It should last forever if it's a good wield and you use the right material, but don't do it yourself get a professional a to do it. Edited August 13, 2011 by F.N.G Quote Link to comment Share on other sites More sharing options...
Rob Leech Posted August 11, 2011 Report Share Posted August 11, 2011 (edited) I'm pretty sure you can't heat treat a re-weld....but someone a little more into metallurgy may be able to shed some more light on the matter Correct, trying to re-heat treat it will only soften it more. It should last forever if it's a good wield and you use the right material, but don't do it yourself get a professionial a to do it. Incorrect, the effect of the HAZ ( Heat Affected Zone) will soften the area and it will crack again, wether it be in a couple of days or a couple of months, it cant be repaired to its original state . From the sounds of it, and from my experience of welding these frames up, i wouldnt bother, leave it until it forms a proper crack then skin it in carbon fiber (or just skin it straight away) - http://www.easycomposites.co.uk/products/starter-kits/carbon-fibre-skinning-starter-kit.aspx Sounds difficult to do, but from my experience, it seems the best way to make a decent repair. Hope that helps, Josh. Oh, btw, have a look at their rod repair kit aswell, might be a bit better for you . Edit- I apologise for the amount of experience shown there . Edited August 11, 2011 by Rob Leech Quote Link to comment Share on other sites More sharing options...
aener Posted August 11, 2011 Report Share Posted August 11, 2011 (edited) I'm not a welder/fabricator, but from what I gather from Josh - who IS a welder/fabricator - whilst re-heat treating it will be better than just welding and leaving it, it'll never return to the state it was before being re-welded. If I was in your place, I'd leave it. Any crack in the headtube area seems like a bad plan, but on a Sky, it sounds like suicide. Edit: D'Oh! Edited August 11, 2011 by aener Quote Link to comment Share on other sites More sharing options...
Bionic Balls Posted August 11, 2011 Report Share Posted August 11, 2011 Hi there- not posted on here for ages but people have some funny ideas about welding! theres no science when it comes to cracks, could crack straight away could last ages place your chips Yes there is. Lots. http://en.wikipedia.org/wiki/Fracture_mechanics http://en.wikipedia.org/wiki/Materials_science I'm pretty sure you can't heat treat a re-weld....but someone a little more into metallurgy may be able to shed some more light on the matter Yes you can. In an ideal world where there were no other complications we'd probably heat treat every weld if we could! Heat treatment gives restores the properties of the parent material before we welded it. Yes you can, but you'll have to find someone with an oven big enough! bingo. Nah, it f**ks with the original heat treating as far as I'd heard? yes it does. Welding makes it very hot.. It should last forever if it's a good wield and you use the right material, but don't do it yourself get a professionial a to do it. some terrible spelling but near enough.. An aluminium frame will theoretically never last forever though (search for "fatigue limit" if you want to know why). Incorrect, the effect of the HAZ ( Heat Affected Zone) will soften the area and it will crack again, wether it be in a couple of days or a couple of months, it cant be repaired to its original state . the heat affected zone will soften yes, but i'd be surprised if it's a non-heat treatable alloy. Chances are it's either 6 (Al-Mg-Si) or 7xxx (Al-Zn) series aluminium which can be heat treated quite easily if you have a big enough oven. If you want to know how, search for "precipitation hardening". Other big issues with welding aluminium are using the wrong filler (for 6xxx alloys use 4043A or 5356 and for 7xxx alloys use 5556A) and not cleaning the joint enough before welding (difficult on frames as you won't really be able to clean the inside of the tube easily- you should if you can though). Any more welding issues while I'm here?! Adam Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted August 12, 2011 Report Share Posted August 12, 2011 (edited) what are you on about? yes get it welded, if you take it to some one decent with a tig it will be ok. and as you said you dont do hooks then there is very little amounts of stress in that area. so it will last around 4-6 months but if you do start doing hooks it will be off in weeks. What longer than the warrantee? BWahahahahahahahahahahahahahhahahaa! Edited August 12, 2011 by Matt Vandart Quote Link to comment Share on other sites More sharing options...
Rob Leech Posted August 12, 2011 Report Share Posted August 12, 2011 (edited) Hi there- not posted on here for ages but people have some funny ideas about welding! Yes there is. Lots. http://en.wikipedia.org/wiki/Fracture_mechanics http://en.wikipedia.org/wiki/Materials_science Yes you can. In an ideal world where there were no other complications we'd probably heat treat every weld if we could! Heat treatment gives restores the properties of the parent material before we welded it. bingo. yes it does. Welding makes it very hot.. some terrible spelling but near enough.. An aluminium frame will theoretically never last forever though (search for "fatigue limit" if you want to know why). the heat affected zone will soften yes, but i'd be surprised if it's a non-heat treatable alloy. Chances are it's either 6 (Al-Mg-Si) or 7xxx (Al-Zn) series aluminium which can be heat treated quite easily if you have a big enough oven. If you want to know how, search for "precipitation hardening". Other big issues with welding aluminium are using the wrong filler (for 6xxx alloys use 4043A or 5356 and for 7xxx alloys use 5556A) and not cleaning the joint enough before welding (difficult on frames as you won't really be able to clean the inside of the tube easily- you should if you can though). Any more welding issues while I'm here?! Adam No offence to you pal, but it sounds like you dont know too much about what the heat treating process does to aluminium. If your saying it's ok to put a previously heat treated aluminium section back through it's last stage then you've not quite thought it through, yes, the area around the weld may well return to its previous state, but what about the rest of the frame? The only reason you can harden these series of aluminium is due to their composition and the way the alloyed elements react when heated to a solid solution, where the particals are rearanged, resulting in a greater resistance to shifting dislocations, so simply adding more heat will cause this structure to be broken down, ending in a softer material. It sounds like you may well have funny ideas about aluminium in general. Cheers, Josh. Oh, and what your saying further up about restoring the properties of the parent metal through heat treating, is called normalizing, and cant be done with any aluminium alloy . Edit- Not trying to be arsey about this btw, you wouldnt believe the number of people that think these things about aluminium because their mate works with steel, 'tis not tut same lad. Oh, and i could write you a book on precipitation hardening if you'd like, no need for that. Edited August 12, 2011 by Rob Leech 2 Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted August 12, 2011 Report Share Posted August 12, 2011 I concur Quote Link to comment Share on other sites More sharing options...
Bionic Balls Posted August 13, 2011 Report Share Posted August 13, 2011 (edited) No offence to you pal, but it sounds like you dont know too much about what the heat treating process does to aluminium. I do If your saying it's ok to put a previously heat treated aluminium section back through it's last stage then you've not quite thought it through, yes, the area around the weld may well return to its previous state, but what about the rest of the frame? You'd need a separate ageing treatment.. And no, it wouldn't be a local treatment- the whole frame would likely need heating. The only reason you can harden these series of aluminium is due to their composition and the way the alloyed elements react when heated to a solid solution, where the particals are rearanged, resulting in a greater resistance to shifting dislocations, so simply adding more heat will cause this structure to be broken down, ending in a softer material. Different areas will be heated at different rates and to different peak temperatures. Some areas could harden due to particulate coarsening. Normalising would only return the parent material to it's original properties if it was normalised to start with. No engineering aluminium alloy I can think of would be supplied like this. No offence to you- you sound like you know a fair bit, but I do actually do this for a job.. Adam Edited August 13, 2011 by Bionic Balls Quote Link to comment Share on other sites More sharing options...
MonsieurMonkey Posted August 13, 2011 Report Share Posted August 13, 2011 Teehee! Quote Link to comment Share on other sites More sharing options...
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