Brazing Stainless Lugs - Setup and Heating

[False Flats]

Hi Everyone,

Apologies if this has been discussed previously and I missed the thread when searching.

Looking for some input from those who have experience brazing stainless. I've built a dozen bikes over the past few years, but only one with stainless lugs. That build went ok, but I did struggle with heat control while brazing - things seemed to go from not ready to way too hot in an instant.

I was using Fillet Pro and Stainless Light flux, an imitation Victor 0 tip and the Oxy/Acetylene both at 5psi. Prior to fluxing, lugs were sanded with new 80 grit and wiped clean with isopropyl alcohol. Same process for the tubes. Went about heating things up the same way I would with a mild steel lug - medium/small neutral flame, repeated sequence of movements around the joint to heat while watching for flux to become glassy/transparent. Frame was brazed in a Bringheli Jig.

Any suggestions/improvements for setup and preheating would be greatly appreciated.
I'm looking for people's opinions on the best methods to prep the joint, get it up to temp and keep it there.

Just getting started on a new bike with stainless lugs using same filler/flux/torch. Happy to post photos as things progress if it helps move the discussion along.

Thanks in advance.

[e-RICHIE]

Have you tried lining up a row of SS lugs and some mitered pipes and brazing them, so as to develop a sense of what is happening and what is different with the material? I would suggest making the investment in parts, and use some off-cuts from pipe you already have. Also, I use at least a #2 tip on all my joints and would suggest that a #0 is too small. A cigarette lighter throws a bigger flame! PS You never want to do more than a small tack when the frame is fixture-ed. After that, braze it free hand without any clamps constricting its movement.

[Jonathan]

Were you really using fillet pro? Is that a typo?

[False Flats]

Richard - Thanks for the suggestions. I have some extra stainless lugs I'm not going to be using for this bike. I'll line them up and give it a try.

With regards to tacking, I'm assuming that I would run a sequence similar to what you would do for fillets, e.g. obtuse ctr, acute ctr, 3 o'clock, 9 o'clock?

Jonathan - Nope, not a typo. Did some practice joints beforehand and got things to flow ok. Realize that 56 Pro or similar would be more suitable. Will switch over to 56 Pro for future joints.

[e-RICHIE]

On the tacking - it all depends on what's being held, and where.
On the lugs - great to read.
Good luck there.
PS turn up the heat and show the fukcer who's boss.
The worse thing you can do is be timid.

[afwalker]

Is fillet pro not good for stainless? Maybe it won't flow far enough so it works for fillets so is 56 pro better?
I've only done a stainless crown on a fork with columbus max blades and the fillet pro worked fine, but I was using a #2 tip.
I had some questions on using SSL flux and fillet pro on those darn stainless water bottle bosses that I kept scorching, so I asked Wade at Cycledesign how to do better and here was his reply, maybe some of it pertains to the heat control you seek:
"
Hi Andy,

The issue is likely to be both your cleaning procedure, and torch technique.

Stainless Steel develops a thin, high temperature chromium oxide layer
on its surface. This layer prevents the filler from flowing.
It needs to be removed by physical means. Usually it is sanded off.
after the surface is mechanically abraded, it needs to be re-cleaned.
An alcohol, or acetone wipe usually works well.
Brazing should take place within a short time of cleaning, less than
an hour would be preferable. Clean both the inside and outside of the
braze area as best as possible.
Flux should be allowed to stay on the surface for a few minutes, to
allow it to chemically remove any remaining oxides.

The next problem is the shape of the boss. It sticks out. Any time
you have a surface that sticks out, it catches the heat of the flame.
Keep the tip of your torch so the heat angles away from the boss, not
towards it as would seen sensible.
With a neutral flame (not oxidizing, it will ruin everything), heat
the area around the boss. Stainless dissipates heat faster than
steel, so it takes a bit more heat.
More heat requires a larger tip, or flame, and not moving the torch in closer.

The flux has 5 stages- paste, fluffy, fluffy with dark speckles,
globby liquid, thin liquid. You are up to temperature when the flux
changes from globby liquid to thin liquid.
At this point the stainless should just start to develop a red tint.
To dark a red tint, and everything will burn. Once the flux goes
thin, place your filler on the intersection between the tube and boss.
Flick the flame onto the silver, and it should melt and flow around
the joint. You may need to quickly move the flame around the boss to
get silver flow and penetration all of the way around.


So in general, you are overheating the boss, when the tube is not yet
recepitive to the silver. Clean everything well, check your flame,
and heat the area around the braze first.

Brazing stainless is difficult, but not impossible.
You can get some inexpensive practice materials at the hardware store.
A few nuts and bolts are great to practice with.

Let me know how everything goes, and don't hesitate to send more
photos, or call.

Thanks,
Wade"

I was pretty impressed with his timely and helpful reply, I bet you can ask him directly and he'll help you out:)
cheers
andy