What is the effect on silver flux when tacking vs. pinning a joint?

[guido]

I am a newbie builder learning silver lugged construction, so please excuse my inexperience. I did a bit of searching but could not find an answer to this...

I have been getting good results fluxing the joint, pinning it, removing it from the jig and brazing in a vice. As i am setting up to do the chainstays on my current project, an acquaintance who does some bronze brazing, suggested I skip the pins just tack braze while in the jig and finish it as I currently do.

My concern with this is that it takes the silver flux through two heat cycles and would risk overcooking the flux, risking poor penetration etc... My impression is that the flux for bronze might stand up to this better, but that is from very little experience with bronze.

With silver flux (Cycle Design System 48) am I better off pinning and using just one heat cycle? Or should I just practice good heat control and don't worry about the two cycles?

Thank you in advance for any advice that can be shared!

Guy

[Eric Estlund]

If you are concerned because you are nuking the flux, slow down and run some more practice. Tacking should be a low impact experience for you and the bike. It is pretty common to tack in the fixture and braze free from it, but that doesn't mean it should be done without concern if you are having trouble controlling heat at the tacking phase.

I'm not a pinner, but we just had a thread about it you can reference back too. There has also been lots of discussion about pinning and tack/ braze cycles on the Framebuilders Google Group/ old list serve. Mine those archives a bit for some good reading.

[e-RICHIE]

After all the pipes are set to length, I drill holes for pins. These are locater points for the reassemby (with flux etc) rather than safety-nets in case something moves. Once the joint(s) is attached, fluxed, pinned, whatever, I'll still tack something on it somewhere. Then I'll check all of it for linearity. Then I'll flux the ever living shit out of it and actually braze it. The initial tack, and the subsequent adding of more flux and then brazing the parts - these have nothing to do with each other such that you'd need fret over what happened to flux layer one.

Sometimes, people read (or think) about pinning and assume "old ways" or similar. No one I know is hearth brazing with any regularity, and the method (pinning) is rooted in it and served a very different purpose then. Using pins now is just one small and minimally tiny time consuming task that will allow a maker to set the pipes up in a fixture while using the least amount of force and stress needed. In other words, never trust your fixture to yield precise centerlines if/when all the pipes are under load. A good one (fixture) will help keep the frame design in place. And when mine (a Bike Machinery Hydra) is loaded, I pin all the interferences so that when ready to reload and heat, the fixture parts are backed out and the pins and holes they're driven through recreate the original geometry.

Explanations like these come with too many nuances and interpretations. I'll have to leave it at this: trust me, this is one process I've figured out and am recommending you apply critical thinking to. There are reasons to spend the extra 10 minutes per frame to do this.

[guido]

Eric, Richard - Thanks for this.

I'm not really having issues nuking the flux with how I'm working now. When I am brazing the full joint, pinned, fluxed well, I work at evenly heating the lug and bringing the flux from crusty to liquid, big bubbles to tiny bubbles and it is ready to take silver. Then I use the heat to pull the silver through the joint.

To tack properly then, is the process the same but just on a small very localized scale so only the flux in the specific area of the tack goes through the transition?

Richard, it is interesting how you flux multiple times in your way of working. What this does to make sure you have good external coverage is clear. I wonder though about the flux in the spaces between logs and tubes? Does it re-melt when re-heating for the main braze?

Thanks again!

Guy

[Eric Estlund]

So long as you haven't overheated it, the flux can happily support a tack then braze cycle.

Tacking is just that- a quick securing dab to lock parts together. Tacks are not structural.

This is a sort of terrible photo of a tacked front end, but shows some tacking. If you look closely you can see a wee bit of silver holding everything in place, but the original flux is still peachy. If I was feeling like I wouldn't have enough to bring me through the full braze I could add more to the cool frame.


This one is brass brazed and shows a little better color contrast. In this case the insides were heavily fluxed, but I was a bit lighter externally for the tacks. I added more before going for the full bb pass.

[e-RICHIE]

Richard, it is interesting how you flux multiple times in your way of working. What this does to make sure you have good external coverage is clear. I wonder though about the flux in the spaces between logs and tubes? Does it re-melt when re-heating for the main braze?

I never wonder.
'Never gave it much thought.
By the way, here are two recent images that depict the flux applied:

1) https://www.instagram.com/p/BB5qECNHqI2/
2) https://www.instagram.com/p/BBqrlsFHqE2/

PS You have to reimagine the task; tacking and brazing are two different processes. Don't worry about the flux. It'll do its job.

[guido]

Thank you both. Much appreciated!