How To Weld A Frame

Postby crazychris on Mon 17/Jan/11 8:58am

I broke my bike. It must be to do with the size of my arse, but the frame where the seat clamp is has snapped at the weld, and as I'm due for a new bike at the end of the year, I'm looking for a cheap solution to see me through the next 8-10 months.

Is there a magical glue I can use? Would cable ties and duct tape suffice? Should I just ride it and get used to the twisting and turning seat? How much (and from where) could I get this welded, bearing in mind the seat post lives in that hole too, so it would have to be a fairly good job!

Typically, my 10+ year old Giant is still going strong despite daily use.
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Re: How To Weld A Frame

Postby Trail on Mon 17/Jan/11 9:11am

Aluminium frame? Not quite as easy to weld as a steel frame, but there should be someone around that could tack that back on for $50 or so (sorry, I do not know where in Chch). When welding aluminium there should be a heat treating process afterwards to get the frame back to the right strength, but as it is not structural break, you might be alright if it is simply welded back on the top.

Will probably have to weld and then use a reamer to smooth the inside of the tube so that your seatpost will fit back in there.

For $50 you could probably almost pick up another similar frame and put all the bits across??
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Re: How To Weld A Frame

Postby Trail on Mon 17/Jan/11 9:13am

Oh, and check how much insertion your seat post has past the bottom of where the crack is. You would typically want a couple of inches of post below the break. If it is too short and you get it rewelded it will be likely to break there again easily.
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Re: How To Weld A Frame

Postby Trail on Mon 17/Jan/11 9:16am

Other super bodge option, if the seat post does go a couple of inches below where the break is you could simply drill a hole through the frame and the seatpost and put a bolt through there to hold it in place :lol:
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Re: How To Weld A Frame

Postby crazychris on Mon 17/Jan/11 9:25am

post goes down inside the frame a good distance, probably another 4-6 inches. It's ridable with it in the current state, just not safe/comfortable when you take it offroad and the seat goes this way and that.

I have considered a new (used) frame and started looking, but not many XL/XXL hardtail frames about :( The bits on the bike are worth way more than the assembled bike, and I don't love (or even like) the frame, so I have considered the drill & bolt solution, or some kind of metal glue down the tube, insert seat post and hope it's at the right height!

If I could find a $50 weld job, I'd be happy with that!
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Re: How To Weld A Frame

Postby Trail on Mon 17/Jan/11 9:32am

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Re: How To Weld A Frame

Postby musta on Mon 17/Jan/11 11:50am

Yup head to Welles St, he has done a lot of bikes
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Re: How To Weld A Frame

Postby philstar on Mon 17/Jan/11 2:02pm

if you have a seat post that is 2-5mm smaller in daimetere, you could get a piece of tube welded/glued into the inside of the the seatpost and stick a clamp on the top of the new tube (slit cut in the top). tube sizing is the key.
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Re: How To Weld A Frame

Postby Simonius_Titius on Tue 18/Jan/11 4:53am

If your tubing is 6061-T6 then welding will take away the -T6 and most of its strength, up to 80%!! Heat treatment nukes the paint and if welding warped the frame one way then heat treatment might fix it or make it worse, there is a significant reject rate at the factory.

7075 tubing relies much less on oven treatment, it strengthens usefully over several weeks at room temp, traditionally while on the boat from Taiwan. I think that might be all they do for cheap frames, better ones get a wee dose of the oven too. So 7075 might work with a tack job.

Aralditing in a sacrificial seatpost as a sleeve as mentioned above seems a lot safer. Don't let the cleaning solvent get on the BB seals. If you end up needing to shim then beer cans are about 0.15 - 0.2mm thick and are a suitably hard/strong alloy.
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Re: How To Weld A Frame

Postby Nick_K on Tue 18/Jan/11 10:02am

I'd never consider riding a frame with such damage. At least you are living up to your user name ;)
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Re: How To Weld A Frame

Postby Percy Pig on Tue 18/Jan/11 11:28am

Nick_K wrote:I'd never consider riding a frame with such damage. At least you are living up to your user name ;)

I would, repaired properly it would be fine, the borken bit does feck all as far as frame strength goes. All its doing is holding up the seat clamp.

But as Mr Titius has said, if its welded heat treatment must be applied, or it will fail spectacularly as the repair weld is going to be right next to and over existing structural welds. :)
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Re: How To Weld A Frame

Postby Nick_K on Tue 18/Jan/11 11:33am

I'd be worried the welds of either the top tube to seattube or seattube to seatstays have also been damaged.

Sounds like more hassle thans its worth imho.
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Re: How To Weld A Frame

Postby danose on Tue 18/Jan/11 11:37am

Nick_K wrote:I'd be worried the welds of either the top tube to seattube or seattube to seatstays have also been damaged.

Sounds like more hassle thans its worth imho.


yep - I'd go with Trail's bolt thru fix - except make sure it's two bolts (ideally at 90 degrees to each other and few inches apart) since they'll be loaded in shear and you want some backup if one lets go. Assemble with seat at right height, drill, pull apart, stuff some epoxy/jbweld down the tube (to stop the post creaking) and reassemble.
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Re: How To Weld A Frame

Postby Simonius_Titius on Wed 19/Jan/11 11:34pm

Nick_K wrote:I'd be worried the welds of either the top tube to seattube or seattube to seatstays have also been damaged.

Sounds like more hassle thans its worth imho.


Are we not New Zealanders? How about cut a few Speights cans into thin strips, mix up some Araldite and paste on aluminium strips just like making a lampshade by glueing layers of paper squares onto a balloon. Then wind dead inner tubes around to squeeze out the excess glue.
The whole seatlug :p area would now be securely encased in bodgeium.
With well chosen original can colours and clearish Araldite it would be a thing of beauty.

Or to be boringly practical wrap it in one layer of glass fibre then bind up with carbon fibre like a negative version of a Vitus carbon frame. There are products which etch the alu to help the bond but a real man would just chew the ends of the tube to roughten the surface.

As an alternative to cutting a slot in the seatpost liner, if you find a sacrificial seatpost with an ID of 26.2(?)mm you can use a self-expanding quill stem from a cheapie Peugeot Carbolite 103 frame. (Super Vitus steel frames are a tad wider at 26.4mm).

Even better, since an internally sheathed seat tube is extra strong you can now just bodge a quill stem wedge onto a seatpost. I saw one that used a hub QR mechanism inside a seatpost to pull the wedge up.
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Re: How To Weld A Frame

Postby crazychris on Thu 20/Jan/11 7:32am

I gave it to the pilot and he threw it out the window.....

Hmmm... nope.

I dropped it off at the airport and a nice chap there (Paul) is going to hit it with a hammer, or however welding happens, so hopefully I'll be in the hills and offroad soon!
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