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Repairs to mig welded steel frame?

Old 12-29-16, 02:00 AM
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Repairs to damaged Tig welded steel frame?

To any tig welded frame experts out there
I am considering buying a rare-ish 90's steel framed bike - tig welded construction. The top tube has been crushed at some point - seller calims it is OK but for purchase purposes I am going to assume it needs to be repaired and wanted to find out if repairs can be done with a reasonable result.


Is it possible to repair damage such as this? - can the top tube be removed or would it be a case of cutting out a section and inserting a new section with internal sleeving at the junctions - staying away from the original headtube/seatube welded junctions.


I am guessing that removing the tube in entirety would be a messy job and that the seat tube and head tube will be hard to weld neatly a second time(?)


Would appreciate any thoughts/knowledge

Last edited by dadoflam; 12-29-16 at 02:03 AM.
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Old 12-29-16, 03:22 AM
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You can bring it to a builder and see if the dent can be eased out with frame blocks, before resorting to replacing the tube, although the simple (compared to lugged/brazed) Mig welded, lugless frame construction might make tube replacement cost closer to the cost of labor to do frame blocking. Only way to find out is to consult a builder....
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Old 12-29-16, 03:27 AM
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I have no firsthand experience, but IMO these are the circumstances that would warrant such a frame repair:
  1. I'm equipped to do it myself
  2. I have a buddy that will do it for cheap/free
  3. the frame is special/valuable enough to warrant the cost of a professional repair & repaint
If none of the above are applicable, I'd be looking for a replacement frame, bare, or if necessary, from a donor bike.
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Old 12-29-16, 03:59 AM
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thanks old's cool - this one falls into category three - one of about 25 ever made to my knowledge. Still checking the authenticity.
I was definitely counting on a professional repair job - wasn't sure how this sort of thing would be approached and/or whether it was a 'beyond repair' situation for this type of frame construction. With lugged frames there are good old school frame makers in these parts who would braze a new tube in without too much problem.
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Old 12-29-16, 05:26 AM
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Old 12-29-16, 05:37 AM
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As is often the case there will be many opinions on something like this. I would encourage you to seek out experts in this discipline specifically. My recommendation would be to consult Dave Levy of Ti Cycles in PDX, he is an expert in repair of all things bicycle frames, especially when it is difficult and challenging.


Originally Posted by dadoflam
thanks old's cool - this one falls into category three - one of about 25 ever made to my knowledge. Still checking the authenticity.
I was definitely counting on a professional repair job - wasn't sure how this sort of thing would be approached and/or whether it was a 'beyond repair' situation for this type of frame construction. With lugged frames there are good old school frame makers in these parts who would braze a new tube in without too much problem.
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Old 12-29-16, 09:21 AM
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If you cut internal sleeves and inserted them, then how could the new replacement section be put in place? Unless they are with no more than a mm or so stickout, then the frame spread slightly to insert the new tube. Even then though the internal sleeves really wouldn't contribute much if any to the strength of the new welds.

I would just have the new section welded with a double V butt weld at the joints, meaning the old section is chamfered at the end, and the new section is chamfered, then the weld fills up those areas. The resulting weld in theory can be just as strong as the parent metal. No internal sleeves.

I'm not a skilled enough welder to pull off welding on such thin wall material without distorting it, but I have seen welders who could. There's a couple of things TIG welders will do to show off their skills: one is to cut two beer cans off in the middle then weld them back together with a butt joint. Quite impressive, takes a very steady hand and control of the arc. The other is to weld two razer blades together lengthwise.
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Old 12-29-16, 09:33 AM
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Images for framebuilder time, of note cut a main triangle and things get pretty limber. And you will find out fast any built in stresses in the frame!
I would not want to sleeve it but I would measure, mark, cut insert and then braze in the sleeves, spring open the frame, insert the replacement section then silver that in.
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Old 12-29-16, 09:39 AM
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Welding in a new section would be a hack repair, at best, IMHO. Just as difficult as welding in an entire new tube, so why bother.
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Old 12-29-16, 10:11 AM
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Rare doesn't always mean valuable.

What is the bike/frame you are considering?

Photos of the bike/frame, and the damage?

Also once repaired, and painted, it will remain as a repaired/painted frame that will naturally decrease its value.

I might consider the repair on something very special like a super-rare funny bike. But, probably not on most other frames... other than attempting a home repair.
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Old 12-29-16, 10:31 AM
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There are not many frames worth the cost of quality repairs (new top tube) and quality paint/decals and take the lose in value for being a respray unless it is a labor of love. Does not sound like this is a labor of love so pictures, please.
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Old 12-29-16, 12:22 PM
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It's not really complicated to remove a tube from a TIG welded frame, just cut a chunk out of the dented tube, grind/sand off the old welds, miter a new tube and weld it up. If you are handy with a file and a measuring tape one could buy a new top tube from NOVA, do the coping yourself, cut out the damaged tube yourself and just take it to a regular welding shop, they charge less than framebuilders it seems to me.
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Old 12-30-16, 06:53 AM
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This isn't heat-treated steel, is it? If so, the entire frame will have to be re-treated, which means the cost to repair might be prohibitive unless the bike has sentimental value or is collectible.

Non-treated steel should be straightforward for anyone with a TIG welder to handle. I've had things done by the welder just down the street, and that was more than enough to ensure integrity in garden variety Tange Infinity tubing.

It'd be best just to replace the entire tube, since one can never vouch for the integrity after major damage.
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Old 12-30-16, 09:42 AM
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Originally Posted by nashvillebill
I would just have the new section welded with a double V butt weld at the joints, meaning the old section is chamfered at the end, and the new section is chamfered, then the weld fills up those areas. The resulting weld in theory can be just as strong as the parent metal. No internal sleeves.
The point of creating a groove (you mentioned welding a double V groove) is that it lets you penetrate into thick material when welding. In this case the tube is very thin so penetration wouldn't be an issue. In fact you would want the tube thicker at the weld so as not to get "melt-through" at the joint (hence the sleeve suggestion). A sleeve would act as reinforcement, a heat sink, and would keep the tubes square to each other during fitment.


Also, a mod might want to change the MIG mention in the title to TIG. As far as I know MIG is not used for bike fabrication.
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Old 12-30-16, 11:17 AM
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Originally Posted by TenGrainBread
The point of creating a groove (you mentioned welding a double V groove) is that it lets you penetrate into thick material when welding. In this case the tube is very thin so penetration wouldn't be an issue. In fact you would want the tube thicker at the weld so as not to get "melt-through" at the joint (hence the sleeve suggestion). A sleeve would act as reinforcement, a heat sink, and would keep the tubes square to each other during fitment.


Also, a mod might want to change the MIG mention in the title to TIG. As far as I know MIG is not used for bike fabrication.
I don't disagree with your logic; a sleeve lets the welder turn up the heat enough to get full penetration while minimizing blow-through, and with higher heat there's no need to chamfer the edges (by chamfering I meant basically breaking the sharp edges down, since the wall thickness is less than a millimeter).

I have indeed made internal sleeves to butt-weld thick-walled aluminum tubing (for the lock bars on my cargo trailer). One hassle to making internal sleeves is that the outer diameter (OD) of the sleeve must match the ID of the tubing, ideally it would be a tight locational fit. I have a lathe so it wasn't a big deal to turn the sleeves to the right size, but I don't know if the OP has that option available. So my thought was to eliminate the sleeves and have the welder, assuming he/she is skilled, turn the heat way down while still achieving a full penetration weld. Easier said than done.

Which ultimately brings me to my (revised) conclusion: Whether using an internal sleeve, or butt-welding without an internal sleeve, this in all probability will look like a kludged repair job. The weld must achieve full penetration all the way around, since any nonconformities will introduce stress risers and possibly begin cracking. Plus, when the weld is complete, it won't be a perfectly flat surface all the way around. Best case, it's a convex ridge all around that can be carefully ground and sanded flat and smooth. That's a whole lot of work and very tedious. Worst case, there's undercutting (depressions and incomplete filling) at places in addition to the raised ridge. The undercutting will require filling with body filler before painting. Undercutting also introduces stress risers and since the material is thinner there, the frame may fail.

So while the frame could be repaired by cutting out a bad section in the middle and butt-welding a new piece in, IMHO it's not a great solution, at least not for a frame that supposedly is worth a lot of money. My thought now is that the best solution is the earlier suggestion of cutting the tube out entirely and replacing the whole piece. Grinding the old welds off won't be much more work (if any) than trying to grind new butt welds perfectly smooth. Now there would be a smooth new tube, with no stress issues.
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Old 12-30-16, 12:38 PM
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If you're putting a sleeve in, then brazing is also a possibility.

I'm wondering if one could make one's sleeve(s) loose enough that they could be pushed into the uncrushed section of tube. Then using a string, thread, or wire through he headtube and/or seattube pull them into place. Then braze into place. Welding is best with a tight fit, but brazing works well with a slight gap around the sleeve.
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Old 01-01-17, 09:22 PM
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Ok – I made the decision and bought the bike. It is a Banesto Team bike made by Dario Pegoretti in 1993 and ridden by Jean Francois Bernard during the 1994 season including the TdF where he supported Indurain to his 4th victory. (and the last TdF won on asteel bike)
This bike ticked a few boxes for me – the key ones being that it is a Pegoretti (which I have always quested after), a vintage Pinarello (which I collect) and a 90’s era steel bike with early Campy ergo shifting (I don’t have) all in one.
When Dario replied to my email and very kindly confirmed that it was one of his it was enough to take the gamble on the dents either being minor or repairable – I am pretty stoked to have got it.
Dario indicated that it is made with Excell tubing which I had not come across before. A bit of Googling gave me a bit to work with including that it has a different composition to many products makingit light, strong but also a bit harder to work with.
The dent on the right hand side is the one I am concerned about



















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Old 01-01-17, 10:52 PM
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Heck, if it can’t be rolled out and the alignment is OK, I’d just document its history, maintain it well and ride it a lot. Any repairs, even if near perfect, are going to undermine the value.

Cheers,

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Old 01-01-17, 11:33 PM
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Originally Posted by merziac
As is often the case there will be many opinions on something like this. I would encourage you to seek out experts in this discipline specifically. My recommendation would be to consult Dave Levy of Ti Cycles in PDX, he is an expert in repair of all things bicycle frames, especially when it is difficult and challenging.
My thought exactly when I saw the OP's post. Tig welded frames are bread and butter for TiCycles. So is repairing anything steel (not just bikes). They are not cheap but you will get the word on if the repair is feasible, how it should be done and what it might cost.

It's a given that they have seen damaged tig welded bikes. The biggest market for theirs is as winter bikes for local racers. Those bikes don't get babied.

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