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 Post subject: brazing query
PostPosted: Mon Jan 06, 2020 3:44 pm 
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Joined: Thu Aug 13, 2009 11:28 am
Posts: 156
Hi all, firstly a vintage 2020 to you.

Now for the question which comes about because 13 months ago I had a very bad fall and totalled my right knee so I’ve done Some but very little flying since however I have built a couple of vintage RC assist free flyers.
Now I know it’s not a specific esoaring question but I need to solder the undercart of a Junior 60 and there’s bound to be someone who has done similar so am I right in assuming trying to soft solder 8swg wire is not an option even if the join is bound together with thin copper wire. This leaves hard soldering (brazing) which I have never tackled. My main worry is that the steel at the braze will be softened and bend on a heavy touch down.
If anyone has experience of brazing and can spare the time to, please send advice.
Many thanks
David


 
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 Post subject: Re: brazing query
PostPosted: Mon Jan 06, 2020 7:26 pm 
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Joined: Thu Oct 06, 2016 5:16 pm
Posts: 66
I have used bound and soldered u/c joints for years. Mainly in 10swg and 8swg, also for support struts on biplanes etc. in my experience this joint can be very strong indeed, in fact only the very worst crashes have seen damage to the joints.
I guess that it is important to make a good joint, so clean wire and the use of a separate flux will help there.

As a coincidence my soon-to-be ready Junior 60 will have such joints, with around 10-12mm of the joint bound with single strand copper wire.
I will admit, a nicely brazed joint might look neater, but may also remove some of the wire strength (having been red hot).


 
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 Post subject: Re: brazing query
PostPosted: Tue Jan 07, 2020 10:42 am 
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Joined: Wed Dec 20, 2006 1:32 pm
Posts: 855
Brazing/silver soldering, is he best way to go for heavy wire guage joints. It can be off putting if you have never done it before, but once tried, you will find it quite simple to do, having used the process over many years in the engineering side of my work.
I had to do a similar job on an Aeronca Sedan undercarriage that used 6swg wire. Not having access now, to a supply of the materials needed being retired, I purchased a silver soldering kit, of the silver solder plus flux, from E Bay. You will need a propane gas torch that will give high heat pencil flame. Prepare the joint to give a good contact area and clean thoroughly. The two parts need to be held together, in position, so as they cannot move. A piece of flat metal clamped to each half, to hold them is the way to go, mole grips or in my case I used toolmakers clamps which I still find useful for the odd job.
The flux comes in a white powder form, which is mixed with water in a small quantity, to make a thin paste, not to thin so it runs off when applied to the joint.
Heat the joint up, so as the flux becomes liquid and the joint will be close to being dull red. Heat silver solder rod, dip into the flux powder or the mix, so as the flux attaches itself to the rod. Apply the tip of rod to the joint with the heat being played onto joint, till the silver solder flows. You might need to put more flux on the joint to get the braze/solder to run. Very satifying when the braze/solder runs to make the joint.
Some years ago there was a low melting point braze brought out by Eutectic Company, but have not seen it for some time now.


 
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 Post subject: Re: brazing query
PostPosted: Wed Jan 08, 2020 5:14 pm 
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Joined: Thu Aug 13, 2009 11:28 am
Posts: 156
Thanks Dave and Brian
Your comments have been very helpful and I was keen to try brazing however my concern is does the anneal the steel and create a weak leg?
I'm still weighing what's best but in the scheme of things it's not the end of the world and both as described seem to work.
Laughing
David


 
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 Post subject: Re: brazing query
PostPosted: Thu Jan 09, 2020 4:05 pm 
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Joined: Wed Dec 20, 2006 1:32 pm
Posts: 855
David T wrote:

Thanks Dave and Brian
Your comments have been very helpful and I was keen to try brazing however my concern is does the anneal the steel and create a weak leg?
I'm still weighing what's best but in the scheme of things it's not the end of the world and both as described seem to work.
Laughing
David


Never known it create a weak spot as long as you do not quench it in water,to cool down, which can if done when in the hot(red state) make it brittle, as piano wire has a high carbon content.


 
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