Hi.

I've bought a cheap custom Tig welded frame and would like to smooth out the joints and thought this would be a good oportunity to try out some fillet brazing. Is this a bad idea?

Thanks.

Go for it. Just make sure you remove all paint/primer first.

This method has been used to make lugs with (out of two tubes). Also at least GT has used this method to make frames with. Andy.

Very many years ago Jamis offered a bike that was tigged first and then had fillets laid of that. They advertised it as the best of both worlds. In reality the tig was bad and it was then covered with fillets that weren't much better and then lots of bondo to make it look good.

You may have issues with getting the fillets to flow and wet out as they should over tigged joints. It depends on what rod they used and how well it was cleaned when they welded it originally.

dave

Wont all the heat weaken the tubing? I thought TIG is OK since only a little of the tubing is heated, and brazed frames have the lug to add some strength, but Braze over TIG would seems to be sketchy

Thanks.

Yeah, maybe it's not the best idea. I think i'll use some fine filler instead.

Filet brazing was developed when shortages of materials in wartime made the building of lugged frames difficult and it was discovered that this construction method was just as good although more time consuming than building a lugged frame due to close mitering that is required in the respective joints.

This is a method that has also been used on quite a few frames and there are some notable frame builders who have also used filler to correct less then perfect brazing work or to get a more aerodynamic shape that would be impractical with brass.

By using filler you will not have to worry about affecting the existing joints or cooking the tubing... in some cases you may have to use a good amount of what is expensive brass which would involve longer heating cycles while filler can be done cold.

Schwinn use to use solder as a cosmetic filler over the welded or brazed joint. Andy.

If you just want to smooth over the welds, or would settle on that, you can tig silicon bronze.

I've used epoxy compound to fair tig weld and it works well everywhere but bicycles where there is a prejudice against doing it, though it is a great way to simply smooth stuff out if you aren't trying to prove anything.

I would keep the practice brazing on practice pieces.

Lots of Stainless filler wire is used on Tig joints , make sure its plain steel on the bead , first.

It's perfectly fine. Check out Herbie Helm's site as builds his own lugs in this same method. His lugs will blow your mind. I love this one piece head lug.

Check out his Flickr page as Herbie posts up quite a few photos of his customer builds step by step. Page 13 gives a nice group of shots of his custom lugs from tig welded to fillet brazed and overall form cut out.
https://www.flickr.com/photos/helmcycles/page13/
Helmcycles.com

Herbie is not using TIG for his bilaminate construction

Sorry for the confusion as I got confused flipping through the pages in his album of his TIG'd lugs and the fillet brazed lugs. It's crazy looking at the pictures online and then seeing it in person at Doug's shop.

I'm pretty sure Rene Herse (the new one) are making their 650b lugs with this method. I have a V/O stem made that way, and so far it hasn't broken...

If you want to clean up the appearance of the welds, a material you might consider is the German made Devcon Stainless Steel / Epoxy putty. This stuff is pretty commonly used for non-load bearing repairs in my line of work. It's pretty durable and takes a reasonable surface finish. It has about one quarter the density of steel or brazing filler, so for a given size of fillet this method will not add as much weight (if you care about such things). It isn't cheap.

If you primarily want brazing practice, that's a different issue.

If you have no experience brazing, there is a high change of screwing up with the torch. Better to find something else to practice on?

AFAIK, Rene Herse does TIG+fillet for the lugs, then uses silver to braze the tubes.