Is this the case for a seat tube reamer?

[Alistair]

Duane,

what kind of flux are you using here, and what's the capillary gap/clearance between the tubes?


Alistair.

[duanedr]

Hi Alistair,
I'm using Gasflux Type B flux. I am working with 1.125" tube with .058" walled 1.25" sleeve.
thanks

[Alistair]

The flux looks pretty cooked. You got it too hot at some point. That doesn't bode well for the flux in the capillary gap. Once the condition of the flux goes south, you're unlikely to get much filler to flow.

I would try a bigger tip, with a softer flame. You should be aiming to get broad areas of the tube up to temp at the same time. I see a good amount of filler on the outside of the tube, suggesting that you're adding rod before the joint is ready to accept it.
Don't be afraid to soak some real heat into it. Keep the torch moving. Read your flux, and to a lesser extent the color of the metal. That will let you know when it's go time. That way, the filler will suck right in there.

Looks like you could use more flux too. Don't be afraid to scoop it up with the end of your rod, as it sags down the outside of the joint, and deposit it back at the top of the tube, to keep the metal well protected.


Alistair.

[Alistair]

One other thing. I'm sure you're doing this but it doesn't hurt to check. Are you finish sanding the OD and ID of the tubes in a longitudinal direction? Those scratches, parallel to the direction that you want filler to flow, aren't completely essential, but they do help things along, in my experience.


Alistair.

[duanedr]

Are you finish sanding the OD and ID of the tubes in a longitudinal direction?
Alistair.

Nope. I'm going round and round. I'll add this to my next attempt. Completely obvious now that you mention it.

It's very frustrating as my fillets turn out fine with no burned flux or brass and my silver lugs look like glazed donuts (give or take).

thanks as always and back to the bench.

[Alistair]

Yes, brass brazing lugs is quite different to silver brazing them. I probably did the equivalent of 7 or 8 front triangles, in practice lugs and BB's, before I felt like I was ready to do a decent job on an actual (brass brazed, lugged) frame.

Btw, in case it wasn't clear, when I said "softer flame" I meant a carburizing flame ie. one with a small to medium sized acetylene feather.


Alistair.

[EricKeller]

I have been searching threads for a while now and can't find the right one - this one seems pretty close.

nobody will criticize you for starting a new thread, but to me this ancient one is inappropriate.

As far as your question goes, don't fill the sleeve all the way through. And you should use silver. It's not going to remelt when you fillet with brass.

The reason that you are cooking the sleeve is (probably) that your torch isn't big enough. I have completely filled a 3" sleeve with brass, and at first it wasn't satisfying. I got the biggest tip that my acetylene tank could safely support and it was much easier. I still wouldn't do it on a frame, that was just practicing for brazing lugs with LFB

[duanedr]

nobody will criticize you for starting a new thread, but to me this ancient one is inappropriate.

As far as your question goes, don't fill the sleeve all the way through. And you should use silver. It's not going to remelt when you fillet with brass.

The reason that you are cooking the sleeve is (probably) that your torch isn't big enough. I have completely filled a 3" sleeve with brass, and at first it wasn't satisfying. I got the biggest tip that my acetylene tank could safely support and it was much easier. I still wouldn't do it on a frame, that was just practicing for brazing lugs with LFB

Yes, I had a feeling a bigger and softer flame was at the core of my problem. I have little boy tanks so, I didn't want to push the tip/flame size.

Knowing that I can use silver and don't need to completely fill the gap makes things much more manageable.

Thanks as always to both of you for sharing your expertise.

[Alistair]

What size acetylene tank do you have? You're right, there is a limit to how much acetylene you can draw off a given sized tank, in terms of cubic feet per hour. You can "under drive" a particular tip, to a certain extent, but since tip cooling relies on gas throughput, you don't want to go too low.


Going up a tip size or two, and running a less aggressive flame, is going to give you the lower gas velocities (softer flame) that you might find helpful ie. Gentler/broader heat. It's a bit like the flame that oxy - propane gives you. Some people prefer the broader more general heat that an oxy - propane flame gives for lug brazing.


Alistair.