Brazing compound joints

[gone_wheelin]

I tried searching but maybe I am searching for the wrong topic.

I was wondering what to do when brazing multiple tubes to the same location, compound joints?

Here is a pic I found for comparison. Notice where two tubes meet at the rear/top of the passenger area:

I was doing a little practice brazing last night and found that when I got the joint hot enought to braze a second piece of tube, opposite the first piece, the first joint also heated up and the joint failed.

Do I need to just mock everything up and braze these types of joints all at once?

Thanks in advance,

 

[Double J]

2 things I do..

1. just braze the one end that doesn't meet at the intersection (ie like and x) Then when all the pieces are at the center point braze them all at once.

2. sometimes you can't do #1 because of changes or adding support to a point. what I do in this situation is heat the pieces as close to the meeting point but not directly on it as possible. Then when you are ready to add the saft silv move your heat directly on it add the silv and let it work into the joint.
What this does is warms the meeting point with out melting the silv and letting you attach the silv to the added point, then when both are heated both joints braze togeather with the old braze and new.

let me know if this helps or you need a demonstration. I can take a video.

 

[gone_wheelin]

Thanks Double J, that makes sense.

I going to stop by Harbor Freight or a welding supply shop to pick up some items, such as magnets, to help be hold these odd shaped pieces before I move on any further.

Thanks again.

 

[roktoy]

Yep...what he said.

You can bias the heat onto the new tube and apply just a little heat towards joint area and "tack" the joint. Then come back later and finish brazing the whole joint with all the tubes.
Jay

 

[Mike Poulson]

2 things will make brazing the 2 joints easier,
The fit between them needs to be perfect.You can reheat a joint that is fitted good without a failure.The problem I see is when brazing is filling a gap in the joint and when it's reheated it falls out.
If you notice in your example photo the top tubes that run front to rear are firmly attached and can't move if the middle joint is reheated.



-MikeP

 

[gone_wheelin]

Thanks for the great suggestions guys.

I figured that once I start getting the base frame assembled, it will help hold the brace pieces in place, thus helping aid in keeping the joints in tact. Then I was practicing, the previous joint was not held in place by anything other than gravity.

I've got a race this weekend so getting prepped for that will take priority. I should be able to get back to the building after this weekend and will probably start a build thread once I get a little bit done.

 

['83 chevy]

some of the compound joints i have done before, all i did was put little MIG tacks on the pieces, then came back and brazed it