ppg677

I've read in various forum archives that many people claim MAPP can be used for brazing (while others claim it is impossible).

I have a steel (reynolds 531) stripped. The three slotted housing guide braze-ons were previously knocked off by some fixie-loving arse :-) Since the frame is stripped, I'm tempted to give brazing a shot for these tiny non-structural parts rather than using the little clips to hold the cable.

What's my liklihood of success and damage? Silver solder, right? Can I just use some kind of C-clamp to hold the tiny part in place?

Unfortunately not a whole lot of YouTube videos. There is one that I partially watched and I recall a couple things (flux that turns black is too hot, and bright red is too hot but dull red is OK).

I'm not going to buy a oxy-acetelyn setup, but I'd spend up to $100 for the fun of it. I figure that's what it would take for a MAPP torch, solder, flux, and the braze-ons.

busdriver1959

I've had bad results with c clamps. When the flux heats up, it gets slippery and the c clamp will fall off because its weight isn't centered over the tube. If you bend a spoke in some way to hold the brazeon in place, you will probably have good results. I've tried all kinds of solutions and a spoke has been the best answer by far. I have bent some like this to hold something down with a finger, others have a little bump that conforms to the shape of the brazeon that work better in some instances.
i started out using MAPP/OXY. It worked for small stuff. The OXY bottles are small and run out pretty quick.

Andrew R Stewart 

MAPP does ok for some thin walled and small massed brazing with silver. (BTW are you referring to 56% silver brazing rod? I am.) It's when the area, mass, temp levels get larger that MAPP does not provide enough thermal energy (note it's not as much about the temp of the flame).

But before you start to scorch tubes and burn flux I strongly suggest you do some practice brazing. Your descriptions of the color and flux condition show a very minimal understanding. Then there's the thinking about using a C clamp to hold the bit in place. Never use a clamping with force method to hold brazing hot pieces together.

Do some archive searching, look at some building photo sets, practice burning up or cold brazing scrap before you touch your frame. Remember you have one chance to get it right. Andy.

randomgear

Just plain Propane will work to do small braze-ons, I've done a top tube guide for my commuter with one - like busdriver wrote, just hold it in place with a bent spoke.

Do not try to pry the spoke off if it sticks, you'll trash the guide - I know from experience. By the time I got the spot up to temp, I had charred about 6" of paint -- more than I had expected to for such a small bit.

Practice on something first - both for brazing technique and the fixturing method. I find nothing is more frustrating than trying to braze up something that keeps moving, but YMMV.

Make sure the silver filler is cadmium free so you don't poison yourself. I used the Weldcote 45CF silver with weldcote white paste flux.

dsaul

A Bernzomatic trigger start torch with a MAPP cylinder and 56% silver will work fine for braze ons. I like to use an old spoke to hold them in place. I simply tape the spoke to the tube with masking tape. Just tape it far enough away from the heat to keep the tape from burning. As Andrew said, practice on something first.

Andrew R Stewart 

And this amount of burnt paint is somewhat because of the low heat and broad flame that propane has, compared to OA. The less focused flame heats up a larger area and the lower energy content requires a longer time spent with the flame hitting the frame. When I do after the fact braze ons I quote about 6" of damaged paint. The customer often thinks this is a lot, it isn't. But it's like doing a roof repair. The hole might only be 6" across, the amount of sheathing replaced grows to 24" and the shingle replacements further grows to 48". With a painted frame, by the time you have sanded the brazed spot and feathered in the surrounding paint and are ready for primer 6" is not much at all. Andy.

Henry III

It's totally doable. Don't make a mountain out of a ant hill. Get some 56% silver, the correct flux and clean it up good. I've had good luck with just c-clamps. I also run a piece of steel rod of some sort through all of guides kind of like a shish kabob that way they're all in kind of inline with each other. You can even use simple banding wire to hold the rod down. Works for the frames that I built or added braze ons to.

JohnDThompson 

For the tubular type guides, a steel rod can hold them in alignment, but you do have to be careful not to braze the rod to the guide. Do practice some first.

Andrew R Stewart 

If you use an Aluminum fixture/holding device you won't be able to braze the bit to the fixture. And with good heat control the AL won't melt much if at all. Andy

malcala622

I used Loctite super glue on my TT cable guides and they have a strong hold. Ive tried snapping them off and they've held well.

FYI this was on a 86 Bianchi

mrv 

I'll sechteple the MAPP/air working with silver braze. I could not get anything but candle wax to flow with propane/air (well, ok, I'd run like heck... but anyway).
I tried it with a c-clamp, got warned it might not allow braze material under the part or the clamp might loosen while you're brazing. So I used the c-clamp as dead weight.
Here's a bunch of photos you can peruse if you like. Three bike projects poorly sorted in the same album. I brazed rack bosses that have not fallen off yet.
https://goo.gl/photos/GiNjLLpLL4nAWHqW6
Cheers!

randomgear

I used a Berzomatic torch with Propane, maybe it somehow burns a bit hotter than a cheapo propane burner.

mrv 

Could very well be. I was using some small-ish torch heads with my propane tanks, so maybe it was just not sucking in enough air to generate sufficient heat. When I used MAPP/air, I upgraded a bit with the head and trigger assembly.