Crashed cross check brazing practice, next step?
 

so I just got a crashed cross check from a friend. The seat stays are bent down at the canti bosses. So I want to fix it while also getting some practice. What is the best course of action? I was thinking cutting of the stays but leaving a bit to use as makeshift lugs my other idea was to cut the stays fully off grind the seat tube and bb shell clean and fillet braze a new triangle on. Are either of the possible? Is one a better option than the other? Thanks!

If it's the seatstays that are bent, just replace those. And yes, it would be better to remove them completely.

that and the dropouts too... the chain stays look to be in fine shape... someone mentioned in another thread about not fillet brazing right to the seat tube. however this frame has no lugs so I will need to do that. any advice or further reading I should look into for this project? could using the ends of the old stays work as lugs anyway?

No, leave the dropouts as is, as long as they are not damaged. Just remove and replace the seat stays in their entirety. If you silver braze to the seat tube you should be OK. Cross Checks have a fairly thick seat tube. If fillet brazing with brass, I would use a heat sink in the seat tube. Using the existing seat stays as "lugs" or "sockets" to slide new stays into could work, but only if they are fairly large and you can find new stays that would fit inside of them.

Dave

should I use safety silv 56 and will that be strong enough? why the heat sink if I use brass? would I need a heat sink for LFB? what sort of heat sink would you recommend?

56% silver is very difficult to build a fillet with, so it's really not a good idea on the seat stays. A heat sink is to avoid distortion. Brass/LFB are two names for the same thing.

If you have tight miters and the tubes are properly prepped and its brazed well, 56% will be strong enough, IMO. However, fillet brazing with LFB is a little more forgiving of technique and would be stronger. As unterhausen says, heat sinks help prevent distortion of the seat tube. There are many different kinds from simple steel "plugs" to fancy expanding brass ones. I use the steel one shown below. If using steel, be sure to pull it out while the weld is still hot, or you might never get it out. FYI....with brass and a heat sink you may still get enough distortion that you may have to ream the seat tube to get the seat post back in.

Dave


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FYI...One way to use 56% on a seat stay and ensure a strong joint, is to "ring" braze it. Which is to say that once you have everything mitered and prepped and are ready to fit up, you can flip the frame upside down and slip a coiled up section of silver into the seat stay (after its all fluxed up, of course, inside and outside). See the photos below.....which, BTW, are for illustration purposes and the stay has not been mitered or fit to the seat tube. Once its all set up and flipped up so that gravity is holding the ring of silver against the seat tube/tip of the seat stay, carefully heat around the joint area until silver just starts to flow out all around the joint. This type of brazing is fairly simple and leaves you with a nice thick fillet of filler on the inside of the say, making for a strong joint, with minimal clean up on the outside. It's easier than trying to fillet on the outside with silver, which, as unterhousen said, can be difficult, especially if you've never done it before. I also like how fast back seat stays look when they have minimal to no fillets on the outside : http://www.andersoncustombicycles.co.../DSCN4308.html

Dave

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