arex

I had a local bike shop repair the seat stay brazing on my Raleigh Sports frame, as well as brazing on a cable stop for 3-speed shifter cable. I'd asked to have them torch off the chainguard mounting tabs, but for some reason they didn't. Also, the cable stop is fine, but the cable housing guide a couple inches up isn't lined up very well with the cable stop.

Rather than take it back, I figured I'd go ahead and do it myself, and got myself a MAPP torch. I thought that there wouldn't be an issue with softening up the brazing on the cable guide to get it aligned a bit better, and to remove the mounting tabs entirely...I was wrong.

There were two issues with my attempts. First, I know I was getting things very hot, dull-red hot, actually, but I couldn't get the brazing to liquefy (or even soften) at all. Do I need to be using flux to help things along, as when I'm soldering electronics, or is there something else I need to be doing?

Second, did getting the tubing as hot as I did ruin the temper, or does it need to get a lot hotter before that happens? If I did ruin the temper, is it fixable by heating it up again and then quenching it? Have I ruined the frame?

Scooper

Your questions could probably be best answered in the Framebuilders forum.

1) Did you use MAPP and oxygen or just MAPP? Just a MAPP torch probably wasn't hot enough.

2) What is the tubing on your Raleigh Sport? If it is one of the heat treated tubesets like 753, it's possible the heat from your torch has weakened it.

3) Reheating braze filler always requires a higher temperature to melt than the heat required for the original brazing.

4) What brazing filler did the shop use? If it was silver alloy, the remelt temperature will be lower than if brass filler was used.

EDIT - Looking at the Raleigh catalogs, it appears the tubing on your Sports is 20-30 High Carbon, so the heat you applied shouldn't have compromised the tubing.

JohnDThompson 

MAPP/air is unlikely to get hot enough to melt the brass, as Scooper notes. You'll want a fuel/oxygen set-up of some kind (MAPP, propane, or acetylene with oxygen). You should use flux to protect tube tube while it's hot. Raleigh "Sports" frames were plain high-tensile carbon steel, not heat treated fancy alloys like 753, and are fairly thick so any heat damage now is likely to be minimal. That said, instead of using heat to remove the chain guard mounts, why not just saw them off and file smooth, espacially at this point when the tube has already been heated twice (once to install the braze on, and again when you tried to remove it). Why take a chance?

arex

1. just MAPP...it was supposed to be suitable for brazing.

2. It's 2030 Hi-Ten.

3. I sort of wondered about that.

4. Brass, I think. It's definitely not silver. I suppose it could be bronze, but to be honest, I don't really know what bronze looks like. I'm assuming brass.

arex

I'll probably just cut and file, then...like you say, why take the chance. The cable guide isn't so horribly misaligned that it won't work, so I'll just live with it.

I'm highly experienced with soldering, but I've never worked with brazing before. I hadn't anticipated that the brass would require so much heat to get "wet".

Scooper

John Thompson's suggestion is a good one; why risk damaging your bike with heat?

For removing braze-ons, I use a Dremel tool with a carbide cutting wheel taking care not to cut too close to the tubing, then use a file to smooth the remnants of the braze-on flush with the tube. For brazing on cable guides, I use a Bernz-O-Matic OX 2550 Oxy-Propylene torch kit, Stay-Silv white flux, and cadmium free Silvaloy filler.
It works great.

Fred Smedley

Would that set up be suitable for adding disk mounts to a old stumpjumer frame, and a brace for the rear?

Scooper

For that application I'd be inclined to use brass filler, and the oxy-propylene setup probably wouldn't get hot enough. A good Oxy-Acetylene rig with the right torch and tip would work.

busdriver1959

If you're going as far as adding disc mounts, you need to think long term and buy equipment that will continue to work well when you expand your horizons and go bigger and bigger on your brazing projects. Before you commit to oxy-acetylene, consider oxy-propane. I've switched and I like the stuff. There's a long thread on Velocipede Salon titled acetylene vs. propane. Lots of good input from Doug Fattic and really worth the read.
Also, consider Cycle Design Group for brazing supplies, especially their flux.

Scooper

+1

Propane is much safer than acetylene and almost as hot. Cycle Design has Fillet Pro filler and SSL flux, both are especially good for working with stainless.

Allen

Moved to Framebuilding from C&V.

Andrew R Stewart 

I sure hope you practice on scrap a lot before modding the frame. There's so much not asked yet that makes me wonder about your experience. Not that this isn't within you're ability to learn... Andy.

busdriver1959

I'm going to disagree with Mr. Stewart. The stuff you're talking about doing is pretty benign. The Stumpjumper has pretty thick tubing and you would have to really do it wrong to cause a catastrophic failure. Steel likes to let you know before it fails. Jump in, the water's fine.

Andrew R Stewart 

Yes the actual brazing isn't too hard to get a handle on although MAP gas torches will be at their upper limits for brass brazing given the thicker section of the brake mounts. Knowing how to limit the time at heat will go a long ways to insuring the blades don't loose more strength/temper then could happen. Other concerns are the fork's ability to withstand the stresses and how that disk brake mount needs to be designed to reduce the chance of an "oh my god" moment.

I've taught a few people how to build and have watched in person their light bulbs going off as they learn how to do stuff. All have later mentioned that they were happy that they scaled down their expectations and went with basic designs and materials for their first frame. Maybe I'm reading into Fred's mind more then is there (which I have been accused of before) but I see some one who needs some torch and fabbing experience before they go forward with modding a fork and brake system (and on a fork that wasn't ever meant for this).

But this is only my opinion and speculation. Andy.

JohnDThompson 

This is another good reason to use a fuel/oxygen setup: with fuel/air, it can take a long time to bring the work up to temperature, leaving a large heat-affected zone. Fuel/oxygen will heat the work quickly and keep the heat-affected zone small.

busdriver1959

[QUOTE=Andrew R Stewart;17116531]Yes the actual brazing isn't too hard to get a handle on although MAP gas torches will be at their upper limits for brass brazing given the thicker section of the brake mounts. Knowing how to limit the time at heat will go a long ways to insuring the blades don't loose more strength/temper then could happen. Other concerns are the fork's ability to withstand the stresses and how that disk brake mount needs to be designed to reduce the chance of an "oh my god" moment.

You're right about the disc tabs. I reverted back to the original post about doing some simpler brazeons like cable stops and guides. Disc tabs aren't in the benign category.