Framebuilders - Adding cantilever bosses with arc welder - safe?
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03-05-06, 09:00 AM
I'd like to add canti bosses to a steel frame without them. There are no frame builders here so am considering passing the job to a skilled guy with an arc welder. Is this a safe way to do it?
He added rack fittings to a fork a couple of years ago and he did a good job (not a problem with them yet). Thanks in advance.
03-05-06, 10:11 AM
Unless this guy is a really skilled arc welder, I imagine he will blow holes in your frame.
Canti studs should be brazed on; a cheap mapp torch does this job well.
03-05-06, 11:20 AM
In fact he's a professional welder. But is this kind of assembly strong enough for brake bosses?
I don't know. I would guess that some factories do it that way.
- Most certified welders are familiar with structural welding in thick metal; fabrication of thin metals like sheet metal, but not in heavily loaded situations; and mild steel not chromoly. Of course there are welders familiar with structural thin tube welding in light guage steels, like aircraft welders, but it is much less comon.
-the problem is that arc welding creates high temperatures that reduce the strength of the underlying tubing, normally this is dealt with by limiting the welding to the ends of tubes where they are thicker. Possibly a manufacturer of cheaper frames has a prcess where the bosses are machine arc welded to a fork, but those may not be high performance tubes. If your bike has high performance tubes in it they probably aren't up for arc welding.
03-05-06, 06:29 PM
I will assume that by "arc welder", you mean "TIG welder". :) If you really mean a guy with a stick (arc) welder, don't do it!
The seat stays are some of the less loaded tubes in a bike, and they're usually not butted i.e., thinner in the middle). I think you will be fine having the bosses welded by a skilled TIG welder. I removed and re-welded the brake bridge to change a 26" frame over for 700c wheels when I was building my tandem; it's been fine.
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