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Tips/Techniques Feedback on Brazing techniques and results

Tips/Techniques

phaxtris

(Ryan)
Premium Member
Premium Member
The zinc is what gives the brass/bronze the yellow color, it looking more copper is definitely a sign you have severely overheated and burn the zinc out of the alloy, the bubbles inside are another, when the zinc is overheated it burbles out of the alloy, and the last indication would be if you were to destructively test the piece by breaking, the break zone is more crystal shaped (like cast iron), brittle, and full of pinholes

You lose a fair bit of ductility and strength when you overheat the braze, you can avoid this by "working" the braze joint less, heat it up, dab the braze in, move on, try not to heat that area longer than nessacary

Back In college we did braze plates as part of the pre-employment course, it was 3/8 plate, bevelled 45 on both plates with a 1/8 open root, set at a 45degree incline, we destructively tested them (broke in half with a hydraulic press) the plates that had the zinc burnt out were full of holes, and broke considerably easier than the braze joints that were properly done, you can also get "zinc chills" (metal fume fever) by burning the zinc out, so something to be avoided
 

Rauce

Ultra Member
Thanks for the tip. Do you try to file a radius into the dropout to match?
Usually there’s a bit of a rad on the dropout edge at least with most stamped dropouts and machined dropouts like paragon ones that are thoroughly deburred. If there’s a bit of a gap there I wouldn’t bother trying to get it perfect.
 

Proxule

Ultra Member
The zinc is what gives the brass/bronze the yellow color, it looking more copper is definitely a sign you have severely overheated and burn the zinc out of the alloy, the bubbles inside are another, when the zinc is overheated it burbles out of the alloy, and the last indication would be if you were to destructively test the piece by breaking, the break zone is more crystal shaped (like cast iron), brittle, and full of pinholes

You lose a fair bit of ductility and strength when you overheat the braze, you can avoid this by "working" the braze joint less, heat it up, dab the braze in, move on, try not to heat that area longer than nessacary

Back In college we did braze plates as part of the pre-employment course, it was 3/8 plate, bevelled 45 on both plates with a 1/8 open root, set at a 45degree incline, we destructively tested them (broke in half with a hydraulic press) the plates that had the zinc burnt out were full of holes, and broke considerably easier than the braze joints that were properly done, you can also get "zinc chills" (metal fume fever) by burning the zinc out, so something to be avoided
Ahh zinc chills.... Good ol moo cow milk to the rescue. Now I just burn the zinc off with a torch prior to welding. Or refuse.
 

Tom O

Ultra Member
I heard that you could put borax on top of the molten brass to slow down/stop the loss of zinc.
 
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