- Steel gurus in da house? can I weld cracked 853?
My tig welded 'conical 853' has developed a crack headtube to down tube 13.6mm one side, and 7.9 the other. I use mig welding a lot in my work, can I weld this (I can of course) but will it change the properties of the 853 through the heat process mainly, to warrant not repairing it? Any other issues I should be aware of before attempting….
Posted 9 years agoPeterPoddyMember
Well all I've got to go on is one pic. And to me, that looks like a paint problem. If you're that sure it's a crack then you'll be ruining the paint anyway, so why not do as Nols suggests and strip a bit of paint off and have a look? If it's cracked, get it off to a framebuilder, if it's not, £30 at the powdercoaters and you're good to go! 🙂Posted 9 years agowwaswasSubscriber
853 is supposed to actually strengthen when welded so I wouldn;t worry about weakenign the frame – the question is really if there's enough metal there to actually successfully weld that'll hold together afterwards.
Even lookign at the pic I think the crack is nearly at the top of the TT – past that blob of sealant there.Posted 9 years ago
Paul, yep spoken to Thorn, all their frames have a lifetime warranty, one of the reasons I bought it. But, they no longer make that model, the Sterling replacement they offered me is horrible, more of a touring bike with v bosses as well as disc, gone is the Reynolds tubing and it has ride limitations placed on it. No dropp offs etc. Their frame shop is gone too, so we're at stalemate on the situation at the moment. I'm sure it'll resolve itself in the end.
BTW, the pic is of the downtube joining the headtube wwaswas..Posted 9 years agomick_rSubscriber
If you have access to bottles then I'd personally braze it. With a small area like that you might actually manage to braze it with a regular propane torch if no oxy-acetylene. Drill a tiny hole at each end of the cracks first.
You could then also braze on a small 1mm steel triangle gusset over the top on either side – done right it would look fairly tidy.
I would have thought SJS should be coughing up something – new paint wouldn't be an unreasonable thing to ask for (it is pretty obvious this isn't crash damage).Posted 9 years ago
Dave Yates has got back to me, and advised not to repair it, especially as there is another similar crack appearing on the other side.
I do remember tightening up my headset/stem before the ride as I recalled some creaking, the last time – now I know the answer to that one!
SJS are still out on this one.Posted 9 years agomuddy@rseguySubscriber
Pete, the only kind of repair I can think of is a bit of a bodge and would involve fabricating and welding on a strengthening plate under the downtube to try and even the load out. Otherwise it may require some pretty extensive (and probably pointless) surgery with a new headtube and possibly a new downtube too…
Pity as I always liked that Thorn.
You could always ask Dave Yates to build a lovely new 853 frame for you 8)Posted 9 years agofattatlassesMember
I've got a little bit of metallurgical training, but specialise in er…'special steels' of other types (amongst other things). I'll be honest, welding of 853 isn't my specialism, so I wouldn't like to give a definitive answer. As you no doubt know yourself, there's a bit more involved in the application of air/self-hardening steels in this application.
If it's of interest, I know a very experienced chap that might be able to advise (he's also a cyclist & fan of steel frames), so if you want, I can drop him an email (if you could PM me a couple of photos of the crack it might be a help). The chap is thoroughly enjoying his retirement though, so it might be a week or two before I hear back off him – as he's normally off bike-touring, munro-bagging or grand-kid sitting!Posted 9 years agoMacavityMember
"but will it change the properties of the 853 through the heat process mainly"
a curious question
"The chemistry of air-hardening steels like our 853 and 631 means that not only are they stronger than typical chrome-alloy 4130 type steels, but after TIG o r MIG welding, the heat-affected zone (HAZ) will be significantly stronger due to the grain structure formed on cooling in air. The positive result from this is a higher fatigue life for the joint – usually 30-60% better than an equivalent Cr-Mo joint. So less material can be used to achieve a particular target fatigue performance."
"by 'bronze welding' (not brazing) new head and down tubes in"
bronze welding is probably slang for brazing.
Silver soldering is slang for brazing using silver based alloy.
Before cutting out the old head tube and downtube either measure the angles of H/T to Top tube and H/T to D/T plus D/T to seat tube. This will give you a guide for replacing them, or markout the layout by drawing around the frame with it placed on a large sheet of paper or plywood for example. This will make checking the new tubes easier before welding / brazing. Or there is the opportunity to change the head angle if you want, but requires some care and thought.
You can get a selection of tube thicknesses in 853 or 631 or any steel you like. Thicker wall thickness might be the better option (lower stress, stress = load/area).
If you have air tools and rotary-burrs / small belt-sander then cutting out the old tubes will be easy, but with care though to leave a smooth and even surface on the old H/T and BB shell to be brazed to.
"Waxoyl"Posted 9 years ago
to braze anything it needs to be clean, very clean, so any waxoyl needs to be thoroughly removed.
yes I have since discovered that bronze welding and fillet brazing is the same technique. My concerns over the heat, was re-heating a previously TIG 853 joint – the top tube. I should have made that clear.
I probably won't actually do the work, if I have it repaired – other than perhaps paint. Although, it wouldn't be inconcievable as I do have some oxy/acetelene kit, no bottles anymore – yearly rental was too much for the use I got from it.
CheersPosted 9 years ago
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