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Author Topic: Any hints on how to braze brass tube?  (Read 3983 times)
elShoggotho
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« on: March 30, 2010, 09:33:43 am »

I've got a problem here. Namely, it's a piece of 2" diameter brass tube fit for my next pair of goggles. Since I'm a semi-crafty man, said toy boiler tube shall become part of my next pair of goggles. Since I don't want to use lots of J-B Weld this time around, I want to braze it. Thing is that I can't get the tube up to temperature.

So here's my question: What's the minimum torch size (or different approach) to get a 52mm brass tube with 1mm wall thickness to the melting point of cadmium-free silver solder?
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Captain Shipton Bellinger
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« Reply #1 on: March 30, 2010, 10:20:51 am »

Mmmm...

Are you intending to braze multiple pieces to each tube? If so you could be in for an interesting time...

I'd suggest using two torches; one reasonably heavy plumber's-type torch which you keep constantly playing over the body of the tube, and a smaller torch which you then use to get the localised heating on just the area of the braze.

It takes a bit of practice, but by using two torches you end up with the bulk of the work piece hot enough to allow the smaller torch to give precise spot heat for fine brazing. It's the method I used on this goggles project.

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elShoggotho
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« Reply #2 on: March 30, 2010, 12:52:06 pm »

My goggles aren't fully scratchbuilt. I want to braze the front of standard German welding goggles to that brass tube. Along the way, I had the idea to cut grooves into the tube, to have less surface to heat. Could be done artistically, with a dremel wheel and drill holes, for a rounded end.
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jringling
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« Reply #3 on: March 30, 2010, 04:02:33 pm »

Curious what you have tried to use so far... A standard sized plumber's torch should be able to heat the tube. Heat from the inside of the tube to minimize the heat loss. I have soldered larger tubes this way...
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fciron
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Getting it hot and hitting it hard


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« Reply #4 on: March 30, 2010, 04:13:46 pm »

Unless that brass tube is a lot thicker than I am imagining any torch should work. You don't do the whole thing at once, but work your way around.

You want to warm the whole assembly with the torch to prevent too much distortion; Tack it in place by soldering a few parts around the joint; Finally, work your way along the whole joint with torch. You should be drawing a long a puddle of molten solder and adding solder when it gets low. The solder will flow to the heat as much as towards gravity, so it's possible to do a neat job with a little care.

As always, I recommend practicing on scrap metal in advance.
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elShoggotho
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« Reply #5 on: March 30, 2010, 04:36:43 pm »

Curious what you have tried to use so far... A standard sized plumber's torch should be able to heat the tube. Heat from the inside of the tube to minimize the heat loss. I have soldered larger tubes this way...
I tried to use a jeweler's torch. Fine point, runs on lighter gas, with adjustable oxygen intake. Enough to solder brass wire, but trying to heat a spot on a brass tube of considerable size gets tricky.
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gyxile
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« Reply #6 on: March 30, 2010, 04:47:49 pm »

have a search on you tube for 'soldering brass '  or  'soldering copper' there are quite a few demonstration videos  on there that may help you out.
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elShoggotho
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« Reply #7 on: March 30, 2010, 05:10:43 pm »

Finally managed to get a good alloy going. Cut a groove into the tube, about 1 millimetre before the end, connected to the main tube at four points. I even bridged a few gaps with silver solder. I might get an all-round connection going yet!

Expect the results to hit the bay of E in the next days. A fully brazed monoggle on a chain.
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Mr. Boltneck
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« Reply #8 on: March 30, 2010, 06:11:11 pm »

This is why I do most of my silver-soldering with a biggish propane/air or MAPP/air hardware-store torch. For anything bigger than fine jewelry, a typical jeweler's torch does not have the heat output to keep up with the ability of brass to radiate heat away.
Along with the two-torches method, you might also look at how the piece is supported, and look at ways to provide some thermal insulation or retention. Sometimes, just putting a few fire-bricks around your soldering surface will reflect/retain enough extra heat to make the difference. I have also known things like dental plaster or casting investment to help, as you can use them to both fix parts in place and insulate them for soldering.
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sidecar_jon
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« Reply #9 on: March 30, 2010, 06:26:54 pm »

Brass with its high copper content leaks heat away very fast, use a big torch! and some sort of hearth to stop the heat being blown away, make the join very clean and the gap very small, and i have had good results with "Benzomatic" brazing rods.
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elShoggotho
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« Reply #10 on: April 02, 2010, 05:04:13 am »

I acquired a full scale plumber's torch today, used it to preheat the pipe from the inside. When the blue butane flame started to reflect in yellow, I brazed the goggle part with my tiny hand torch. Worked like a charm.
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