Brazing Fixture

[srobovak]

Hi HMEM,

First of all thanks for this great platform - a huge source of knowledge and inspiration to me.
After sneaking around for a long time I thought I might also share something.

Recently I needed a small 3-way fitting for my hydraulic line. I decided to braze one using some small (OD=4mm) hose nipples from Swagelok. This small assembly posted an obvious problem how to hold the pieces together during the brazing process so that they don't move. The idea here is to show you the little jig I used to hold everything together that worked quite well.

In my experience proper brazing jig needs to meet three requirements:

1) It has to have low heat conductance not to take much heat from the workpiece and hence keep the
brazing time as short as possible.
2) It has to be stable enough so that the parts don't move on you while brazing.
3) It can't introduce too much pressure, otherwise the parts will deform during the heating process.

These conditions are somewhat contradictory so it takes some time to design a proper fixture. And of
course the build of such fixture usually takes much longer that the parts in question or the brazing
process itself...

Following photos show the individual parts, assembly held in fixture, brazed assembly and finally cleaned up finished 3-way fitting.

 

[DJP]

Nicely done. I might have tried brazing one nipple at a time to get easier access to each joint. A jig is certainly preferred and now you can make hundreds.

Thanks for sharing

 

[tornitore45]

Clever.

 

[abby]

Making a jig seems a lot of work for such a job as shown , why not simply make the nipples a push fit into the block and they would stay in position whilst being brazed ?
Dan.

 

[srobovak]

Dan,
For a proper brazing action one needs about 0.05-0.1 mm gap for a capillary action to take place for this work's diameter. If press fitted, the silver solder has nowhere to flow. Moreover, by heating the whole thing above 720°C it could still end up crooked.
But you're right it's not very efficient work for one part. I guess you could try it the way you described, but I think the joint would not be sound. - Brano

 

[clifforddward]

Nice job Brano, thank you for sharing. I always tell folks the set up is often 2-3 times the work of the actual silver soldering...but using jigs assures nice work and results in a part that will prove satisfactory for a long time in the future.

 

[awake]

I just found this thread. Thanks for sharing the process - very helpful, and you got beautiful results!

Just to be sure I am understanding, you are using "silver brazing"? What is the composition of the silver braze?

 

[Carl Reinhard]

At 81 yrs old I'm trying to quote, from memory, a saying by Koto, "An amatuer sets his work up so that a professional cannot get good results, and a professional sets his work up so that an amatuer can get good results."

 

[goldstar31]

You've worn well at 81 but I reckon it was Steven Pressfield who was responsible for the quotation.

 

[user 1616]

Amazing how something so simple can take so much thought and time to actually produce. Very nice idea.

 

[srobovak]

I use "FONTARGEN F 300 H Ultra NT" flux and 1.5mm thick brazing wire with about 55% silver content. Over the years I have found to get the best results when pre-forming rings around the joint and covering them with flux.

However I can't really compare to anything else...

Next time I do some brazing I'll try to make a short video.