Stick welding square tube with 2mm thick wall: any tips?

by Mikel
(Bilbao, Spain)

Hello all,
First of all thanks for setting up this webpage. It has helped me a lot. It is by far the single best source of info about welding.

I am making a sort of bike carrier for my VW van to carry a second spare wheel. Nothing fancy, just two claws that grab the top edge, another two that grab the lower edge of the door and two pieces of square tubing in between tightened so the setup doesn't come loose.

Top claws are done and fashioned out of 3mm plate bent to shape and two 5mm tabs on top of it that also work as ribs (they are as long as the claw itself, following the curve of the plate, making it impossible to un-bend). They are pretty beefy, they are not going to come appart, that's for sure. I welded them with 6013 2,5mm rods. I had a wormhole once but grinded it off and rewelded.

Now I am making the tubings. I made a template with some old rebar to find the correct angles and now I need to do the same... with the square tubing. Since I don't have a bender I intend to notch one side, bend to shape and weld the seams. You can picture a big "C" shape with short arms. It requires only two bends to adapt to the door curve.

Whatever I put together it is usually made of nothing thinner than 3mm because I am not so good at arc welding and I end up blowing holes on it. This time I decided that it would end up too heavy and I choose 2mm wall tubing instead.

Yesterday I decided to make a few tryouts out of scrap 2mm wall rectangular tubing to get a feel of the correct settings for my welding machine, travel speed, etc. I own a Solter CottS 165 inverter machine that has a dial to adjust amperage but no display to show it. I cut a few pieces of it, deburred them and got to work.

I started with my smallest 6013 rods which are 2mm thick at 60 amps electrode positive. First butt welds, like the ones I would end up doing in the sides of the tube once bent to shape. No intended gap between the pieces (maybe just a hair for the pieces not having the greatest fit up). No weaving, just a stringer.

First inch of the weld was ok, after that the heat built up too much and I blew a hole on the tubing (I was welding on the flat position, as usual). Ok, lets make it 55amps. Pretty much same thing. 50 amps seemed to be good enough to make a good looking seam. Since I cut my test pices small I was able to check the inside of the seam and I seems like I was having enough penetration. The slag chipped of easily (but it didn?t peel off by itself) but the ripples where somewhat pointy and the seam pretty flat, seems like I was moving along a bit too fast.

Before doing any destructive test on the pieces (I want to cut strips and bend to see if it holds at all) I decided to test the "T" joints. Just like the ones I will have to make on the inside of the bends (won't be 90º, probably between 45º and 60º). I didn?t change the settings in the machine.

It didn?t go as planed. Blew a hole on the vertical piece after one inch of weld. Turned down the amperage a bit to 45amps. Almost the same thing but? worse. The start of the weld was too cold and I got wormholes filled with slag with no metal joined at all. First inch was crap, next inch or so was OK, but after that I blew another hole.
So as not to concentrate as much heat on the same spot for a long time? I tried weaving (circles actually). And the ?wormhole filled with slag? issue got worse.

In all the T welds I made I had a hard time chipping off the slag. The slag itself had some kind of porosity (looked like an abrasive volcanic stone). Instead of flaking off in big solid chips, I had to beat on it all to remove it. Weld deposit in the best looking parts of the weld was concave and penetration (where I didn?t blew a hole and made it to stick) was ok (I checked from the inside) but again the ripples were pointy.

Anyway, given the equipment at hand and the materials involved? do you have any tips I could try to make this thing happen?

I thought about smaller 6013 rods (like 1,6mm, that's the smallest I can find) so I can run them at the top of their recommended amp range pushing away the slag without melting the whole thing. With the 2mm thick rods I seem to be running them too cold because the arc force does not push the slag as it is supposed to.

Also I could try again with the 2mm thick rods but running them electrode negative? which is supposed to give less penetration. Maybe I could run them as hot or even hotter without blowing holes.

Any help will be greatly appreciated. Thanks in advance!



I would say either use dcen with the 6013 rods
or get some 6011 and try to position the pieces to weld slightly downhill.

6011 will not be as smooth a weld but it will eliminate your wormhole issue

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