Rosette weld ?

[Straightshot]

I'm wanting to support the frame on my 94 Jeep Cherokee, it has a very thin box frame, uni-body.
I was on a Cherokee forum and what they are doing is welding 1/4 x 3 angle to the very thin frame, rect. tube (approx. 3 x 5).
Their drilling holes every few inchs and rosette welding.
I've heard you cant weld directly to the frame (too thin) or it will stress and crack.
This rosette weld reminds me of a plug weld on a differential tube to center section.
I'd like to learn what I can about this weld, if it cam be mig'd or is it o/a ?
It is just to stiffen the frame.
Any help would be greatly appreciated.
Thanks

[FATFAB]

We do something similar on 914 Porsche's They have a week rear section and we plate them over with 1/8" or so thick steel and plug weld them on to the uni-body frame members.

[ligito]

Can you drill and use crush tubes?

[Straightshot]

Fatfab, ligito, in that order.

Fatfab, do you Mig weld those Porsche frames ?

Ligito, sorry but I've never heard of crush tubes.
It sounds fairly basic, is it just drill a hole and push it in and crank it down?

Thanks, Jon

[Miller Swartz]

Jon,

If we were using standard weld terminology, a rosette weld is a plug weld. When doing tubular dragster chassis fabrication, a rosette weld is required when mating two tubes of the same diameter together. Like your application, this is done for strength. Otherwise, the assembly would depend on the quality and strength of the butt weld of relatively thin tubing. Doing so wouldn't be all that strong, or safe.

In this application, a hole is drilled into both main tubes appox. 1-2" from the ends that are being mated together. A smaller tube is then slipped into one end of the main tubes past the hole that was drilled. (For us, the length that the smaller tube is slid into both main tubes is determined by the SFI chassis spec the car is being built to.) We then use the TIG process to plug/rosette weld the inner tube to the outer to make sure it stays in place. That weld assembly is then slid into the other main tube where another TIG plug/rosette weld is done in the other hole, along with the butt weld to attached the two main tubes together. Now this is one specific application with the TIG process, but the result and intent is still the same.

Hope this helps.

[SundownIII]

Straightshot,

Seems to me that 3" x 1/4" would be overkill for the task at hand. If you're looking to "reinforce" the thin frame member, seems that say 1/8" material would be a better choice. Also the thinner material would be easier to "plug weld" and take less heat to the frame than 1/4" material would.

I don't see (depending on location) why you couldn't do this with mig.

[sccatech]

I'm wanting to support the frame on my 94 Jeep Cherokee, it has a very thin box frame, uni-body.
I was on a Cherokee forum and what they are doing is welding 1/4 x 3 angle to the very thin frame, rect. tube (approx. 3 x 5).
Their drilling holes every few inchs and rosette welding.
I've heard you cant weld directly to the frame (too thin) or it will stress and crack.
This rosette weld reminds me of a plug weld on a differential tube to center section.
I'd like to learn what I can about this weld, if it cam be mig'd or is it o/a ?
It is just to stiffen the frame.
Any help would be greatly appreciated.
Thanks

How thick is the box?

1/4" seems to be overkill and the support area too small. I would recommend using 1/8" plate on the top and side and making it as large as possible to spread the load. Rosette welds are definitely recommended. Depending on the thickness of the box section you might have to go down on heat so that you don't blow through the box.

In my case, a Toyota MR2, the box sections are 1/8" and are no trouble but the floor which I have to weld to is 22 gauge and I am having trouble even with .023 wire and as low a heat as I can get.