Best Way To Butt Join Square Tubing

[wvpolekat]

The only reason I went through all this was to stress the attention that should be paid to such a welding step. If the joint is to be made on something that if it fails it is simply an inconvenience, you can take an experimental approach. If it's something with safety at risk, be much more sure of your actions and don't treat the job lightly.

My $0.02,

Agreed. This is just for the 3pt frame of an implement. Worst case is it breaks. But no safety risks or anything like that.

 

[dfkrug]

I have a bad habit of over engineering things and what came to my mind when I read "a butt weld on sq tubing" was a liner welded in first and then inserted and then butt welded and probably a plug weld or 4. my 2c

That sounds like what I do.

Here is a chunk of 2x6x.125 rectangular tubing that I spliced to make
a long box beam.

I like to use sleeves so the the root of the butt weld is stronger than the
surrounding steel, and there is no risk of burn-thru.

In the photo, I have cut and bent 2 pieces of 1/8" steel, which gets
welded inside of one of the 2x6s. Then I fit the 2 sections of 2x6
together and do my butt weld. This way, my sleeve is easy to make,
and tightly fits. I leave a small gap between the 2 sections of tubing I
am about to weld together.

 

[jonyyuma]

Nice description, Both ways, I like that style outside, but if I have the room inside, I use a sleeve. Plus over weld outside, unless very thin. jy.

 

[Car Doc]

I used to buy and rebuild wrecked 4wd Toyota trucks and cars and sell them and I sectioned my share of frames and inner fender structures.

Using a backer or liner welded in first is the only recommended procedure plus it just works great whether welding thin material or thick and you can hide a lot of repairs and not be hiding a potential problem which some re-builders will do unfortunately.

I extended my car trailer axles with tubing inside and a sleeve outside it worked better than that post about the boat that gave me the hebejeebees.

 

[PILOON]

For strength, inner or outer sleeves is the way it is done in aviation.
But welding will have brittle metal near the weld and fracture easily.
The sleeve methods spread the the loads.
Also the splices are not 90 deg. but long tapered slant cuts.
A formula exists that covers the topic and can be found in FAA document known as A.C. 43-13-1A,-2A

 

[Gary Fowler]

Inside Backer plate would be the simplest way to go and depending on your welding skills and the thickness of the backer plate, you would get some additional strength at the joint also. Dont overweld the outside joint by making wider or higher welds than necessary. It wastes welding material and produces extra stresses in the joint. Heavy welds that are more than 3/32" higher than parent material dont strengthen the joint but actually make it weaker and tend to make the joint fracture at the toe(edge) of the weld. The best weld is one that is solid with no defects and flush with the parent material both inside and outside. The weld material used is stronger than the base metal to start with, ie regular structural shapes are ASTM grade A 36 or equivalent chemistry that has 36000 tensile strength while 6013 or 7018 have 60K and 70K respectively so they are nearly twice as strong as the plate that you are welding, therefore if properly welded, there is no need for massive cap passes.