Hi,
Anyone had a frame cracked with these yet? 
Or experiences otherwise… I’m a TIG-guy and would rather skip brazing completely 
(sorry)
My next build is DH/enduro with Velospec 42 x 1/0.7/1 downtube, and I was planning on having 4 bosses on it, for cable management also.
Here’s my example of fusion-welded cable guide on a chainstay:
Looks like you’ve done a nice job with that cable guide. If you’re fusion welding you want to wash some metal down from the thick part you’re attaching onto the thin tube.
I also TIG everything, and I TIG braze these on with silicon bronze (except I weld on V-brake bosses). I’m not brave enough to fusion weld them 
The reason I use braze is to minimize any risk of weakening the tube in its thin section (these bosses and things often land inside the butts). I’m sure TIG brazing is more than strong enough for V-brake bosses but I just want to make sure because you know brakes safety.
We had a discussion about this the other day in which people made the case that any kind of TIG process on these might distort the tube. It’s certainly not a problem I have ever had but it’s an interesting question whether TIG or silver solder results in more overall heat input (it will also depend on the skill of the operator) and another one whether that’s an issue anyway.
I don’t see a big reason to fusion weld them though. It’s always likely to be a bit stronger if you can get a bit of rod in there, and less risk of making a hole or causing damage. I only ever fusion-tack things when I need a spare hand to hold them down with (not the case with anything on a bike).
Looking at the cable guide, you can see that the guide itself is undercut, but the tubing is not. So in that sense I don’t think there is much more to do, at least in this design. Well, maybe the ends could have gone without the weld, as they create a perpendicular stress riser to the tube…
I got a few of these fusion-weld cable guides, but I’m not sure if I will use them.
Yes I don’t usually bother to braze them all the way round. They only really need to be tacked on because they’re just holding cables. Your priority is to preserve the integrity of the tube. Bottle bosses I do TIG braze all the way around. The strength is quite important there because you are compensating for the dirty great hole you just drilled in your tube.
I also did a TIG brazing practice on some 1.0 mm coupons. While I think it is great for lap joints, it definitely did not flow between the pieces, as it would with flux and a torch.
I think you would have to create an external fillet with TIG brazing to rely on.
I used 1.2mm CuSi3 MIG-wire for this. I think it was pretty easy, as this was my first go.
Yes you always create an external fillet with it– a larger one than you would with TIG welding. So your bottle bosses will look a bit lumpy (like they would on an aluminium frame).
I tig braze brake posts. I’ve seen some pretty thin bronze brazing from factory on big name bikes. The size of the fillet is way bigger on the tig brazed, so I feel pretty confident in it.
Yes I’m sure it’s fine. Sometimes brake bridge tubes are only “thinly” brazed on bikes (I mean the kind where you flow the braze in with capillary action rather than building up a fillet) and that sometimes causes controversy since it’s supporting a brake. But idk how often they fail in practice. I TIG braze those. I’m sure TIG brazing brake posts is totally fine.
