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PostPosted: Sun Jan 18, 2015 6:07 pm 
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Joined: Tue Oct 13, 2009 1:27 am
Posts: 2514
Location: Vancouver
Yeah, definitely more comfortable. Cold steel against the face is bad enough indoors, it'd be awful if taking this thing out in cool weather for some shooting. The neoprene makes a warm and soft contact point and shouldn't be difficult to keep clean, being diving suit material.


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PostPosted: Fri Feb 06, 2015 6:54 pm 
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Joined: Sun Feb 10, 2013 1:16 pm
Posts: 1787
I was so impressed with what you had done with the bronze brazing that I went and got some rods to experiment with. I'm not doing very well so far - I think I need some tips! First I tried propane and couldn't even melt the rod. So I picked up a can of MAPP - now I can get the steel glowing red (not sure exactly what flavour of red, I lack experience here obviously), and the brazing rod at least melts - but it didn't seem to flow very well - felt like at least part of it remained very solid. I left the test piece to cool, so I'll be heading downstairs in a minute to see if it took at all. So, how do I do this right? Surface prep, extra flux, oxy - mapp? Are you supposed to get the steel glowing red?

Jim


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PostPosted: Fri Feb 06, 2015 7:32 pm 
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Joined: Tue Oct 13, 2009 1:27 am
Posts: 2514
Location: Vancouver
When I worked at Synchros in the late 80's I used a fine tipped oxy-acetaline torch to braze cantilever bosses to fork tubes, fix broken bike frames, build handlebar stems, and whatever. The extreme heat and pinpoint focus made it about as easy as applying hot glue. Easier once I got the hang of it. I learned on the job. And so far as I know, no one died as the result of my handiwork. These days I don't want to deal with big rental tanks and such, as I have just a 9.5' square shop (if you don't count the huge and awkward built-in shelving area over the entry stairs, which make it more like an 8' x 8' shop if that) and every square foot is accounted for. Big gas tanks, no thanks. So I use a BBQ propane tank from CT and one of these, also bought a bunch of years ago at CT:

Image

For years before that I used a two-tank solution (yet another CT purchase) with propane and oxygen, but the valves were tricky and the oxygen ran out WAY too fast for its cost, so I went searching again and found this one. And it works better. Must be in the porting, as the air blend seems to be just about perfect. With an even older torch (something-Jet, also from CT, bought in the mid-1980's) I almost melted the flow control brass spacer trying to get stuff hot enough if the steel was anything bigger than a finishing nail. With the two-hose, two-valve, two-tank setup I'd spend half my gas just trying to dial in the flame. With this BernzOmatic thing I just turn it up slightly, spark the flame, crank the valve open wide and let go. Anything as big as a few ounces or smaller heats up in a minute or less and provided I've prepared the surfaces well (wire brush, sanding, grinding, whatever) and melted on some of the rod's light green flux coating (I'm still working my way through a tube of brazing rods bought at CT over a decade ago and they're still fine) onto the steel roughly in the area I want bonded, the bronze will flow nicely when the steel on each side is a bright, almost peach orange. Cherry red isn't good enough.

I'm not sure I'm the best guy to explain brazing. It sort of seemed I was a natural when I first picked up a torch. The brazing guy in the shop where I'd just got work, Synchros (mountainbike stuff), one day got frustrated trying to mend a broken, rusty chainstay on a neat old road bike. After half an hour over-heating the steel he gave up, mad as heck. I asked if I could give it a shot. I hit it with a wire brush and file to clean up the mess he'd left, brushed on some of the paste flux the boss said to use, heated it with what seemed to me a good pencil flame of a good blue (don't ask me how I knew), and flowed on some bronze. First try.

And it's mostly just gone like that for me. Somehow soldering is my nemesis, but brazing is easy. Guess I like higher temperatures or something. But it's really easy if you have the metal somewhat clean and get it hot and flow some flux onto it. I introduce the rod (the part now cleaned of most of its rosin by transferring that to the steel) when the steels are glowing nicely, get the bronze glowing almost as brightly in the flame while keeping the steel really hot, then touch it to the steel. And it flows. You want to 'pull' the bronze, not push it. Let the heat bring the bronze towards it, don't use the flame to push the bronze into the crack.

Don't over-heat the bronze once it's flowed. It's easy to boil it and compromise strength if you're using a proper kit. With this budget (about $38 maybe 5 years ago) kit it's hard to get it too hot. Make sure your tank pressure isn't running low, as I find the last 1/4 tank or so makes it challenging with larger chunks of metal. Wide open on the valve, or close to it. About 1" to 2" from the tip of the brass nozzle, you'll have to judge that part as you go, playing with spacing until you get it heating fast. Speed is important.

As you can probably see from the picture, my braze on that barrel nut wasn't perfect. Some bubbling. It was a big thing, and I was brazing stainless tubing to some unknown carbon steel. Many will say that brazing stainless is a no-no, but that's nonsense, it works fine. Sometimes. It's easier to mess up stainless joints, but if you're fast and the work's clean it should stick nicely.


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PostPosted: Fri Feb 06, 2015 8:55 pm 
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Ah, ok. Hotter than I had imagined. My test piece was a half-success. I tried to braze two pieces of 3/8 rod together (it was just what I had in the scraps box). The bronze took to one side, but not at all to the other. The side that didn't take was the side held in the vise that I had trouble warming up. Obviously sinking too much heat into the vise, so I'll need to keep that in mind and find a less conductive way of holding the work. I thought I'd test how well the other side had taken by turning it in the lathe, and that worked beautifully. It's that ability to build up metal and then work it that blows my mind. I'll have to keep my eye out for a torch that I can connect to a BBQ tank. Many thanks for the help.


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PostPosted: Fri Feb 06, 2015 9:02 pm 
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Joined: Tue Oct 13, 2009 1:27 am
Posts: 2514
Location: Vancouver
Oh right, I forgot an important element in enabling faster and more even heating. I cook the steel on a glass fibre kiln brick. Bought one at a jewellery supply place. It's about 3x4x10 and provides excellent resistance to heat waste. Lay your parts out and just braze them on that and you will get up to proper heat is far less time, building much less oxidation. Of course some things you'll want a vise for, or clamps, but I find most stuff can be done on a brick.


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