Field frame repairs and materials

[GideonReade]

Inspired by the thread "Are touring bikes old fashioned"...

We did a big tour, in less developed countries. We had occasion to (easily, twice) find a welder to repair a steel rack, and a steel saddle frame. When a steel fork failed, not catastrophically, we were in a big western city so got a (better) new one. So never needed to weld a frame yet. But widespread use in vehicles means steel welding is worldwide.

But our tour frames are Ti and welders are probably confined to major air force bases. Is that true?

In my engineering career, mechanical colleagues had no issues getting aluminium welded, I don't know how available such is in the wilds?

Once, in the wilds of Wales, on a Saturday, I broke the blade of my carbon kayak paddle. Village motor shop had a glassfibre body kit - cheap stuff, coarse glass mat and poly resin. But I repaired the paddle for Sunday, and it still holds good now.

Resin, especially epoxy, but polyester too, sticks fine to roughened metals. Carbon frames presumably use an epoxy or similar resin inherently.

So to what extent can ally, Ti, and carbon frames be field repaired with polyester resin and glass mat, or epoxy resin and glass/other cloth*?

(*Glass chopped strand mat usually contains a resin soluble binder to hold the random fibres in place, but it isn't soluble in epoxy, so mat/epoxy is an invalid combo.)

[ANTONISH]

Inspired by the thread "Are touring bikes old fashioned"...

We did a big tour, in less developed countries. We had occasion to (easily, twice) find a welder to repair a steel rack, and a steel saddle frame. When a steel fork failed, not catastrophically, we were in a big western city so got a (better) new one. So never needed to weld a frame yet. But widespread use in vehicles means steel welding is worldwide.

But our tour frames are Ti and welders are probably confined to major air force bases. Is that true?

In my engineering career, mechanical colleagues had no issues getting aluminium welded, I don't know how available such is in the wilds?

Once, in the wilds of Wales, on a Saturday, I broke the blade of my carbon kayak paddle. Village motor shop had a glassfibre body kit - cheap stuff, coarse glass mat and poly resin. But I repaired the paddle for Sunday, and it still holds good now.

Resin, especially epoxy, but polyester too, sticks fine to roughened metals. Carbon frames presumably use an epoxy or similar resin inherently.

So to what extent can ally, Ti, and carbon frames be field repaired with polyester resin and glass mat, or epoxy resin and glass/other cloth*?

(*Glass chopped strand mat usually contains a resin soluble binder to hold the random fibres in place, but it isn't soluble in epoxy, so mat/epoxy is an invalid combo.)

I've known of people resorting to glassfibre emergency frame repairs in the past. The glassfibre makes a very strong repair.
I seem to remember someone building a frame using cardboard tubes as a former - he was an enthusiast for this material.
I don't know if it worked .
However if you have a problem with something like a rear triangle, downtube etc it's a viable material for a repair.

[DropperPost]

So to what extent can ally, Ti, and carbon frames be field repaired with polyester resin and glass mat, or epoxy resin and glass/other cloth*?

With composite technology, you're only really limited by your own ingenuity. Fibreglass can create structures of any shape or strength, depending on how you configure it, and how much you use. For example, if you needed to repair a cracked chainstay, you could make the chainstay wider, e.g. by coating in a thick layer of epoxy thickened with powder to form a paste, then bandaging/epoxying it all with glass tape. (The function of the thickening layer would be to make the fibreglass tube more rigid - imagine trying to bend a 1mm diameter plastic tube compared to bending a 2" diameter plastic tube.) You'd want to be using woven fibreglass products - tape, cloth or 'twill' - as these have much better strength. I think you could do a repair on most breaks, although some would need to be big, ugly and heavy. It could be cut off, cleaned and repaired properly when you got back to civilisation. A small packet of fibreglass product would be enough to do any foreseeable repairs. Personally, unless I was doing a ride where a broken bike was life or death, I wouldn't bother, as the resin and activator would be a bit too bulky, even after you've decanted them into smaller containers. Most places in the world will have boat repair businesses etc. with epoxy and glass. (All this probably applies to carbon fibre too, but I don't have any experience with that.)

[wirral_cyclist]

What's wrong with two sticks and twine for down tube splints? And I've seen it done, though I wouldn't ride the version of splinting I saw

[m-gineering]

So to what extent can ally, Ti, and carbon frames be field repaired with polyester resin and glass mat, or epoxy resin and glass/other cloth*?

Entire frames have been built this way, so it is a viable repair technique. On trick with aluminium is to sand through the still wet epoxy to get underneath the oxides

[PH]

I think tubes are probably going to be repairable, in a get you to your destination fashion, whatever the material. Where it gets complicated is stuff like dropouts, I've no idea how one would be repaired without welding.

[GideonReade]

I'm going to add a link, as the discussion has also carried on in this vein in the other thread.

viewtopic.php?p=1746724&sid=d0bb5e3d802 ... 9#p1746724

It's a fair point about dropouts, I'd envisaged cracks in major tubes, or reinforcing a brutally bent back fork. Dropout, err, difficult without replacing the whole thing with a made up bit of plate.

Per forks, I guess it's preferable to stick to the old fashioned head bearing sizes, then something usable can probably be found in most places (but how usable?). Tho I do really prefer Aheadset rather than quill, a case of the modern design being much easier to maintain, but harder to find in the sticks, especially 700C.

[andrew_s]

You can get repair kits for CF, and I've heard tell of people repairing bikes with them, or even taking them as a repair option on tour.

Welding Al or Ti requires a shielding gas, preferably including the rear of the weld, so you won't find a suitably equipped repairer in a random garage or small town.
Ti is sufficiently sensitive to even trace amounts of oxygen that a proper repair requires a gas filled cabinet to do the welding in, so any repair done otherwise should be regarded as temporary.

Steel, on the other hand is easy. I know someone who got a broken down tube welded part way round the Paris-Brest-Paris 1200k Audax, and still finished in time (cracked round from a bottle cage boss).