View Full Version : Brazing for Idiots
12-27-2007, 07:10 PM
OK, time for some brazing for idiots... and I'm the idiot :D.
I need to join some cast iron grape vines to 3/4" x 1/8" angle iron. I tried my hand at brazing today. Using a Harris #5 welding tip, 1/8" flux coated bronze rods.
I thought you are supposed to heat the metal and then remove the flame and allow the heat from the metal to belt the bronze. Well I couldn't get that to work. I was able to heat the metal and then move the rod into the flame and get it to melt, but the flux all burns off.
I was able to get 2 pieces of angle brazed together that way, then tried to braze some cast iron to the angle and didn't have very satisfactory results. The bronze was hard to control and I was able to break the joint with my hands.
So can someone give this idiot a crash course in brazing please? I'm trying to finish up a bookshelf for my daughter.
12-27-2007, 07:28 PM
I would use a #2 Victor, maybe a 3, but I don't know how that equates to a Harris tip....Any way your doing it right....you heat the metal, get it warm, and then with flame and rod you melt it onto the part...the flux appears to burn off but there will be enough to cause cohesion...you may have to put the rod in there and stir it up a bit...it, like all welding , takes practice. For silver braze you paint the part with flux and heat it till the flux starts to melt and you're at brazing temperature...flux is designed to melt at the temp to braze at.
12-27-2007, 07:39 PM
Thanks Rocky. The Harris #5 is rated to weld 1/8", which I think matches up to your Victor #3. I guess it will just take practice. Should I be able to break the joint by hand though?
12-27-2007, 10:52 PM
well i just tried my hand at brazing and not half bad well what i have read is to heat the metal to about a blood red or cherry even better and put the rod onto the surface and the bronze should flow into the metal. but there is one thing that i can reccomend is doing it like tig welding doing the zzzz pattern.
heating the metal to blood red and moving the torch back then dip the rod in then move the torch foward heat the metal again and dip again and keep on doing this.
12-28-2007, 01:03 AM
... Should I be able to break the joint by hand though?
No, you shouldn't.
12-28-2007, 07:11 AM
That's what I thought. The first piece, the steel to steel, is great. The next two, steel to cast iron, the first one I was able to break at the steel, so I thought ok, inadequate heat, bad adheasion. The second one though, I was able to break in the middle of braze itself. Which I knew wasn't good.
12-28-2007, 08:17 AM
couple things, (1) brazing requires a good fit-up, it doesn't fill gaps well.
(2) heat the parts equally, it takes practice when working with dissimilar sections but the brass is drawn to the hotter part and won't adhere to the colder one at all.
when you are at or near brazing temp. move the flame away from the joint, but still heating the part (feather both sections, don't let flame touch the flux coated rod (while it won't affect the joint, all the flux you paid for will melt off). touch the rod to the part for 2-3 seconds, when you've reached brazing temp. it'll melt off and flow, if not, continue heating, repeat. never leave the rod in contact with the part, as you end up with a really bad join (surface adhesion only) touch, flow, touch, flow.
another tip is get some borax at a pharmacy, jewelers supply, or loose brazing flux at the LWS , sprinkle the hot joint, it'll help suck the brass into the joint.
12-28-2007, 04:47 PM
Thanks for all the advice guys. I tackled it today and well, it held, although I do believe I am quite possibly and the crappiest brazer on the planet. :rolleyes: After re-reading the posts I tried to keep all the pointers in mind and amd satisifed with the adhesion, although not the appearance. But that's why I placed the brazings on the bottom of the shelves where they won't be seen.
12-28-2007, 04:49 PM
Here are the brazes.
12-28-2007, 05:34 PM
The first picture looks like the bottom piece was too hot, the others look like they are overall too hot and the last one looks like it was too cold and the brass didn't flow very well. Starting off brazing its easy to use too much heat plus with a #3 Victor/Smith you might want to turn the flame to a low neutral without starving it. First thing I ever did as far as metal work was brazing and I recently finished my O/A class. When you're dipping you should touch the rod to the work, slide it into the edge of the puddle and a little past then stop, once the rod melts pull it out and repeat. The base metal should never glow or get anywhere near that point since if its thin it will end up cracking the base metal when cooling. The bead should look like a fat stack of dimes ideally. I usually heat the base metal up by waving the torch over it a few times and then I melt the brazing rod onto the joint ensuring it wets out but doesn't flow, everything should stay put for the most part. It's easier to start a big glob of brass as a shelf, let it wet out and then build off of it. If it starts to run away from you then let it cool a little with the torch still in the presence of the joint for shielding. Make sure the joint is clean and a gap of .001"-.005" is needed for the strongest of joints and usually gets 4-5 times the filler tensile strength that way, but of course this is decorative. Course it never comes easy, I had more trouble O/A brazing than air/mapp brazing. All I'm really doing is reciting everything I learn from class :D. It just needs a ton of practice.
These samples are a little old and gunky but they've been chipped and brushed a little; once upon a time. This is a tee joint by the way, and they're a pain.
12-28-2007, 06:35 PM
Wow, that's some good feedback Tansit - thanks!
The base metal should never glow or get anywhere near that point
Oh baby, my base metal was definately glowing. I would get it to a dull red before dipping the rod, and once it started to melt I would just lose control of the puddle.
I wish my beads came out like that, but at least now I have something to shoot for.
12-29-2007, 11:42 PM
From the looks of the beads it appears that you might have better luck by moving the flame in a small circle to achieve more even heating of the pieces and the rod, rocking the flame up against the two metals to be joined. As you move the flame, then gradually add in the rod, as the flame circles by. That way the heat is distributed over a larger area, while also melting off small portions of the filler rod tip. Granted, the correct technique requires a very deft touch, but there is no reason you can't get there with practice. It would be very helpful for you to find someone to give you some hands on instruction.
You can spend a lot of time searching for the right combination, but I could have you producing nicely brazed joints in minutes.
12-30-2007, 07:48 AM
Thanks fo the advice Goodhand - too bad I'm not in Montana :(