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Fillet Brazing Practice Questions

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Fillet Brazing Practice Questions

Old 12-26-20, 01:11 PM
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Tandem Tom
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Fillet Brazing Practice Questions

I was able to figure out Metalgeek! Not bad for someone who still has a challenge turning on my Android tablet and tablet!
So a few questions. Is is ok to go back and add brass to build up a fillet? I did a few and I saw some "skimpy" areas so as I am practicing I cleaned and refluxed and added more brass.
Also I used my homemade sandblast cabinet and cleaned off some painted tubes from donor frames. I then blasted a completed braze joint to see how it would clean up the excess flux. Did a nice job. But is this an acceptable practice?
Ir was nice to be in the shop after snowblowing the drive again!
Thanks!!
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Old 12-26-20, 01:16 PM
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I don't think there is anything wrong with adding filler. Many people don't like to re-heat though. Not sure that concern is really supported by materials science.

Not sure why you would worry about sand blasting. Most people use a media that isn't quite as abrasive though.
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Old 12-26-20, 04:17 PM
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Besides the second heat cycle of the adding brass after the initial fillet is cleaned up there's the issue of the likely uneven heat application. This could be addressed with some heating on the joint's fillet that is otherwise fine, after doing the spot addition. Having said that I do add extra brass after the joint is roughed out as needed. I don't push the tube wall thinness thing so am less concerned about witch wandering then some might be.

I generally don't want to sandblast any more then I need to for a few reasons. Since a not cooked joint's flux will just soak off (assuming the flux allows this) using sandblasting to remove the flux seems like a waste of effort to me. Now after I have filed/sanded the joint I do blast lightly and at least once more before the job goes to paint. But these blasting sessions are more about making the surface consistent then any removal of material, flux, brass or steel. Andy
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Old 12-26-20, 07:48 PM
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Tom what some pros do when fillet brazing is to make a 2nd pass while the joint is still hot from applying the brass on the 1st pass to even it out and perfect the shape of the filler. It makes sense to practice on the same joint again adding brass or just playing with the fillet and getting a better feel for shaping it by keeping it in the puddy stage. You are going to throw it away later so whatever you do to it won't matter. The purpose of practice is to get a feel for handling the torch. It takes a long enough time to set up a practice joint so get as much use out of one as possible.

I recommend buying some .035" wall tubing for some practice before you get to your real frame. That is going to be thinner than your junk frame tubing. You will want to get a feel for brazing thinner tubing so you don't mess up when you jump up to making a frame.
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Old 12-26-20, 10:11 PM
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Originally Posted by Doug Fattic View Post
I recommend buying some .035" wall tubing for some practice before you get to your real frame.
Or even .028" (0.7 mm) which is good to practice on if you're considering using modern superlight tubing.
.028 can be hard to fin in 1-1/8" or larger but it's common in 1" and smaller.

Mark B in Seattle
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Old 12-27-20, 02:46 PM
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As I did a bit of practice today I have a question. Does the diameter of the brass brazing rod have any connection to the fillet size? Or maybe I should ask does a larger diameter rod make it easier to make a larger fillet than a smaller one?
Thanks!
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Old 12-27-20, 07:02 PM
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It makes it so you don't have to switch to a new rod as often. I think it's a little more difficult to do a good job with a larger rod, so I think I would skip it at this point of your development. I definitely prefer a larger rod though. On edit: try both and report back what you find.
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Old 12-28-20, 08:51 AM
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Originally Posted by Tandem Tom View Post
As I did a bit of practice today I have a question. Does the diameter of the brass brazing rod have any connection to the fillet size? Or maybe I should ask does a larger diameter rod make it easier to make a larger fillet than a smaller one?
Thanks!
No, a larger brass rod is more difficult to use for someone starting out. Bigger rods and bigger flames is graduate school stuff. What helps a beginner is slowing everything down so their imprecise motions don't have as big an impact. And they have more time to understand and react to what is going on at the joint. That means a smaller flame (and maybe thicker tubes) that takes more time to heat the fillet up and stay within the brass temperature zone between being cold and solid and too hot and runny. Your flame is the on/off heat switch managing the brass's temperature keeping it in that zone. The smaller your flame the less you have to flick the flame on and off the joint to keep it in that temperature zone.

Remember to do the basics of keeping your motions compact, holding the rod very close to the work and placing it in the right position when it is time to add. Slight variations can keep you from getting optimum results. It is so easy to push the rod a little too far beyond the melting zone (which is why if you don't have a very steady hand to support it some way).

Your kinda sometimes classmate Pastor Darrell is still needing to fillet braze his front triangle. Maybe you can pop over for a day while we go over again fillet brazing procedures in preparation for him to continue on his frame?
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Old 12-28-20, 09:10 AM
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Doug, would like to do that!! Will watch the weather!
Let me know when!!

Last edited by Tandem Tom; 12-28-20 at 01:17 PM.
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