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Discussion Starter · #1 ·
I only swore once, a nice loud 'f#ck'. So it goes when learning to build. I was brazing up the chain stays on the practice frame and had everything lined up in the jig. The brazing went OK but I could not get the brass to run all the way round because my jig was blocking my torch tip. So I removed the clamp holding the BB shell and continued. A little better. Then I took the frame out of the dummy axle and started chasing the brass around my joints, just to get them perfect. Got one side too hot, the left, and it fell off, hence the cursing. The heat seems to have changed the alignment of the right side still attached so I need to tweak it back, put the frame back in the jig, line everything up and then rebraze the left one. All in a day's fun!

Drew
 

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Bike Dork
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A simple way to avoid this is a good brazing plan. Don't chase the puddle all the way around the joint, do it in quarters. Look at the joint as a clock face. Tack at 12 and 6. First braze section is from 12 to 3, than 6 to 9, then 3 to 6, finally, 9 to 12. With this you'll always have a solid braze section to hold everything together. Also the heat created by one section is counter acted by heating the opposite side after.
 

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Single Speed Junkie
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themanmonkey said:
A simple way to avoid this is a good brazing plan. Don't chase the puddle all the way around the joint, do it in quarters. Look at the joint as a clock face. Tack at 12 and 6. First braze section is from 12 to 3, than 6 to 9, then 3 to 6, finally, 9 to 12. With this you'll always have a solid braze section to hold everything together. Also the heat created by one section is counter acted by heating the opposite side after.
Please forgive my ignorance as I am still studying on how to fabricate a frame. My understanding of brazing is similar to soldering a joint and getting the material to flow. From an electrical integrity standpoint on solder if you keep reheating the joint similar to the method described above you run the risk of having some sections of the joint being a cold solder joint and is significantly weaker than a proper solder joint. I have seen this on large solder joints on Mil batteries when conducting some FA type work. Of course I'm only attempting to draw a parallel here, but would just like to understand brazing a bit further.
 

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Discussion Starter · #4 ·
Thanks for the tips, TMM. I need to be more careful, since more than 3/4 of the joint was done before I got over zealous with the heat. I definitely wasn't being mindful of where I had been heating the joint, and switching sides and being more patient would have resulted in success. In any event, I realigned everything last night and am ready to reattach the left chainstay but it's pouring rain. Two days after Christmas and it's raining.....


Drew
 

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crux said:
Please forgive my ignorance as I am still studying on how to fabricate a frame. <SNIP> My understanding of brazing is similar to soldering a joint and getting the material to flow.
They are two totally different joining methods. Fillet-brazing (bronze-welding) is similar to tig not lugged construction. Stop studying and start doing and you'll see what I'm talking about really fast.
 
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