Bicycle Mechanics - dented frame
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05-01-06, 05:18 PM
i just came into possession of a 1965 schwinn paramount road frame. tubing is reynolds 531. there's a pretty significant ding in the seat tube and i'm wondering about fixing it. an auto detailer friend of mine recommended hammering a brass tube of the same diameter (27.2mm) gently down into the tube. this sounds sort of sketchy so i'm looking for advice on this technique or any others. thanks for helping me straighten this out (ha. get it?).
05-01-06, 05:22 PM
How about using a brass tube slightly smaller than the seat tube.
as long as you greast the brass tube so It dosent get stuck, and you have a good way to get it out I think It sounds like a good idea.
05-01-06, 05:32 PM
I'm surprised he recommended brass. Normally I'd expect to use a mandrel of harder, stronger material like steel. Gunsmiths "iron" the dents out of shotgun barrels (relatively thin wall tubes) using a cylinder of hardened steel.
05-01-06, 05:35 PM
won't the brass give a bit as opposed to crimping the bike tube?
05-01-06, 06:41 PM
The brass would be a solid piece so it would not be prone to deform, and would not gall or tear the steel tube like a steel bar would.
The steel is already hardened at manufacture and the dent has work hardened that spot even further any additional working of that area is going to impact the adjoining steel before it removes the dimple unless you anneal it some, and then you are faced with re-hardening.
To eliminate this you need to support the tube wall on the outside with a collar as you move the brass plug down and past the dent. The forward end of the plug should be almost spherical and the trailing end chamfered so it cannot bind.
The other option would be to just braze fill the dent and repaint.
05-01-06, 07:36 PM
Learn somethin' everyday ....thank-you
05-01-06, 08:32 PM
^^ditto, thanks for spreading the knowledge before i messed something up.
A friend of mine rides an aluminum bike with a big dent in the top tube. He doesn't seem to care. If you asked him, he'd probably say "why don't you leave it be?"
05-02-06, 01:49 AM
yeah, i probably won't end up doing anything about it but i was vaguely flirting with the idea.
05-02-06, 06:29 AM
Don't mess with it, just put a sticker over it and you'll never know. Steel frames are pretty tough and if it is not out of alignment shouldn't cause you any grief except for the cosmetic aspect.
05-02-06, 07:18 AM
All you need to fix this is piece of common ¾ inch iron water/gas pipe. ¾ is the inside diameter so the outside is a little over an inch so it is a loose fit inside the seat tube. Hold the pipe firmly in a vise and slide the frame over it. Put some masking tape over the dent to protect the paint and with a small hammer tap around the dent against the iron pipe inside. You won’t get it perfect but you will probably fix it so it hardly notices.
Brownell's (www.brownells.com) sells a gizmo that is made to take dents out of thin-walled shotgun barrels. No reason it wouldn't work on a frame tube of about the same size.
Not cheap, though.
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