MIG Tacking fillet brazed frame?
08-29-14, 01:54 PM
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MIG Tacking fillet brazed frame?
Would there be any issue with tacking a frame together with a MIG torch before final fillet brazing? I'm wondering it if may affect the strength of the joint or cause continuity issues. Any input?
09-02-14, 07:38 AM
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Quickness really, with MIG I can just give it a quick tap to hold it in place. How would I tack it with brass, is that like spot brazing?
09-02-14, 08:39 AM
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Yes. Only heat a spot and add a small dab of brass to that point. A tack might only be 1/4" wide. After things cool down and the next steps are done (aligning, more tube set up) add more flux and go back to fully braze. Sometimes a second tack is needed to keep things in line.
Many frames have used a spot weld to tack with, including lugged frames. But since you have the brazing set up already at hand why not just use it to tack with? Andy.
Many frames have used a spot weld to tack with, including lugged frames. But since you have the brazing set up already at hand why not just use it to tack with? Andy.
09-05-14, 01:46 AM
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The downside is that with welding you almost certainly dirty the joint, maybe not if you had tig with a purge. So when you subsequently go to braze the joint it is dirty on the inside, and you will not be able to get the brass to flow in their as easily as you might if you used flux and kept everything syropy as you went through the process of tacking and brazing.
You might think that a brass tack will come out when you go to drop even more brass over it, but it takes more heat to break a braze than it does to apply one, so while you want to get good hot fusion of your brass to the tacks, you should still be able to keep it all together. And of course sequence matters.
And the other problem is that while welding is a superior way to join tubes, tacking particularly with mig is going to create more heat distortion problems than brass should.
And then there is the issue of whether you mean tack with mig and no shield gas, just flux core wire. That is a whole other level of messy.
You might think that a brass tack will come out when you go to drop even more brass over it, but it takes more heat to break a braze than it does to apply one, so while you want to get good hot fusion of your brass to the tacks, you should still be able to keep it all together. And of course sequence matters.
And the other problem is that while welding is a superior way to join tubes, tacking particularly with mig is going to create more heat distortion problems than brass should.
And then there is the issue of whether you mean tack with mig and no shield gas, just flux core wire. That is a whole other level of messy.
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