Brazing cast iron

Just noticed the arm on my Chinese drill press that holds the table is
cracking. Think I'll try to braze it. The arm comes off and it will fit in
my propane BBQ. Will that get it hot enough so I can braze it? Or should I
heat it with a big propane torch? How hot do I want it before I try to braze
it? Don't have a rosebud, about the biggest torch I have is a cutting torch.
Is there a chance that could work? Or should I look for a big tip for my
torch? Could I braze it with a straight acetylene torch? (Prestolite) Have
flux and rod. Going to drill a hole at the end of the crack and grind out a
"V." How deep and wide should the "V" be? Any hints?
Reply to
Big Al
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I would think it should do for preheat if you run it wide open .
I'd think the cutting torch would be too concentrated . It doesn't need to be red hot , it's more important that the heat is uniform to prevent localized stresses .
If you've got enough preheat , the Prestolite torch should work . I'd grind the crack two thirds thru the section , at a 60-90 degree included angle . I brazed a table saw trunnion once ... last I heard it was still in one piece ... the most important part is the post-brazing cooldown . You've got to let it cool slowly and uniformly . I've used wood ashes (big pile , completely cover the part with at least 2-3") , and I hear that vermiculite works well . If you have a charcoal fired grill , it would work well for both preheat and post-brazing cooldown . Hmm , how about a hole about the size of a 3 lb coffee can , build a charcoal fire , preheat , braze , bury the part in the fire and throw a couple of shovels of dirt over it . Dig it up tomorrow after the fire burns out.
Reply to
Terry Coombs
"Terry Coombs" wrote: (clip) You've got
^^^^^^^^^^^^^^^^^^^^^ Slow *uniform* cooldown is very important if the piece is connected back on itself, like a ring or a grid or cross-braced structure. If it's just a support arm with no loops or cross bracing, it is not going to develop thermal stress as it cools. Thermal stress can develop only if one part of the structure is pulling against another part.
Reply to
Leo Lichtman
I figger one can't be too careful with cast iron. From the OP's description , it has machined features . Can't they warp from improper cooldown ?
Reply to
Terry Coombs

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