Framebuilders - preparing joints for brazing fillet?

Should the pieces of metal butt right up against each other at right angles, or should they be filed/ground so there is a little space for the brazing metal to go? What makes the strongest joint?

Do you understand what I'm asking?

Kevin

http://www.imagestation.com/picture/sraid204/pe8e9c8a3148273c9c2062c6185e11c11/ef5b884e.jpg
http://www.imagestation.com/picture/sraid204/pe8e9c8a3148273c9c2062c6185e11c11/ef5b884e.jpg

I did a bunch of reading and I think I stumbled across the answer. For brazing, it looks like you want the pieces to fit as tightly together as possible, and the capilary action will fill the tiny gap that there is. That is how to produce the strongest braze.

It seems for welding, you do want to have a gap to fill, so you would want to grind a little V to fill.

I did a bunch of reading and I think I stumbled across the answer. For brazing, it looks like you want the pieces to fit as tightly together as possible, and the capilary action will fill the tiny gap that there is. That is how to produce the strongest braze.


i have read this as well. google this a bunch, and you may stumble across a graph showing the dependency of joint strength upon tight tolerances

here you go - an excellent resource for brazing

see graph - joint strength maximum at gap of ~0.002", drops significantly once gap exceeds ~0.004". the tight tolerances required and my lack of excess funds and machining tools have kept me from digging into "building my own frames".

http://www.handyharmancanada.com/TheBrazingBook/section%201/The%20six%20basic%20steps%20in%20brazing/Part%201.htm#The%20six%20basic

Yep, thats the site that I found most useful. I didn't absorb the chart when I was reading it the first time though.

The max of 135,000 psi is pretty strong! 60xx series stick welding rods give a tensile strength of 60,000 psi. To get only 60,000 psi with brazing, your gap has to grow to about .4 mm. I'm fine with 60,000 psi. I suppose if things start breaking for me, I can either increase surface area, or take a closer look at my gap. As a hobbiest, I don't think I have to be particularly concerned.

I guess in the future, I'll just try to get the parts as close as possible. Notice that Zero gap still produces a pretty strong braze.

This reveals one advantage of welding rather than brazing for me. With welding, you are making two pieces into one piece. With brazing, you are filling the gap between the two. Welding makes sense in that respect, but brazing is still easier and I don't think this will keep me from brazing in the future.

Kevin

A joint with Vs is only stronger in welding if your welder will not get penetration otherwise. The diagrams in welding books often show pictures like the one above but people don't read the fine print about the part size. A greater concern should be that any accute angles get grond back to full strength.

Fillet brazing I can't help you with.

A joint with Vs is only stronger in welding if your welder will not get penetration otherwise. The diagrams in welding books often show pictures like the one above but people don't read the fine print about the part size. A greater concern should be that any accute angles get grond back to full strength.

Fillet brazing I can't help you with.

So what you're saying is this: If you are welding and are not capable of getting good penetration, then you may need to grind a V. This is usually an issue when working on thick materials. Right?

You lost me on the last part. Could you explain that a little further?


A greater concern should be that any accute angles get grond back to full strength.

Thanks

My good buddy Fred Parr says that the edge of the coped tube should be at a right angle to its surface. I've found disagreeing with Freddy usually leads to bad results - so I've always done my joints this way.

Why? According to Fred, having a sharp edge creates a stress riser that can cause later joint failure. :eek:
Moreover, if the issue was all about how big a gap existed, then there wouldn't be a need for a filet, eh? The filet itself is "outside" of the joint. But in reality, the filet is an effective structural part of the joint. :D In fact the size of the filet should be determined by the strength of the filler used. Weak filler = big filet, strong fillet = small filet.

FYI