more about tubing and rollcages

[havik180]

I've read some advice on here about welding tubing (MIG) and one of the methods mentioned was basically at start, stop , start technique (bascially like closely knit tack welds). Yesterday I actually saw this technique in action on an episode of Extreme 4x4 on Spike. The girl on there was using this technique (well it looked like it to me) to weld a roll cage in a baja Ranger. So my question is , is that an acceptable way to weld a structural piece like a roll cage ? Did anyone else see the show ? I am I right or did I miss something ?


Rich

[snow]

Well, all I can say is that is not acceptable to me.......others may differ.....

I have seen that method used to fill gaps........and one genius I know did his whole chassis that way..........some have used it on thin chrome moly......trying to make it looked TIGed......

Bad deal.......

[Paul Seaman]

This is the mechanical version of pulse, it is another technique that is ok if it is used properly. If used properly! Some will use it instead of learning to do the proper weld pool control while maintaining good fusion. This is balance.

Good luck,

[INTP]

I didn't see the show, but I've seen this kind of welding. I'm pretty sure we're talking about the same thing, so here's my .02:

One of the notable problems with wire feed welding is the cold starts. This technique increases the likelihood that a cold start will mean poor penetration, by adding more starts! I am not saying a good weld is impossible, but a bad weld is more likely.

In my not-so-humble opinion, this technique is a result of a misguided attempt to make the "roll of coins" that seems to symbolize hero worship of the mystical super-welder. For those who don't know how to evaluate a weld, this is a short-circuit way to claim to know the difference between a strong and a weak weld. The irony is that by focusing too much on the "look", the weld is actually made worse.

I think that a series of spot welds is a TERRIBLE idea on a roll cage or any other structural element that depends on the weld for strength.

[INTP]

Since pjseaman responded while I was typing, I'll go ahead and concur with the pulse comment, and add that I have used a start-stop-start-stop technique while welding some very thin metal to control heat. The starts and stops were still close enough together that the starts and stops were barely visible. And it wasn't structural.

[havik180]

It didnt even sound acceptable while I was typing my question but had to ask anyway. But like I also mentioned I could be wrong about what I saw , you know how these shows never show any tech stuff in depth. Hopefully someone else saw the show and can chime in on what they saw. I guess when my time comes I'll just use thinner wire and and try and keep my stops/re-starts to a minimum

[jolane]

I saw that show also, and thought exactly along the lines you are...I was questioning whether that was acceptible. I also had the same thought about cold welds...I would think that the welds would be too cold, especially for a rool cage. They have a TIG available, I saw her using it before.
On a personal note, I think that show stinks technically. I understand the premise of the show, but looking at their roll cage design, I did not feel it was satisfactory. They seemed ot indicate that it was complete (at least that was how I took it), but they had NO diagonal bracing whatsoever...The roof was square, as was the back, just big parallelagrams. I also did not see why the windshield vertical brace had to be two pieces. I don't build roll cages, maybe their technic and their design is perfectly fine, but I would not race in that thing! That show in general is too busy, and I get very little out of it. In contrast, I think Stacy David on Trucks is much better at showing the details!
Joshua

[eric75]

I saw a guy doing that in a monster truck shop I visited. The welds looked good. Don't know if they were strong.

At school we are only have a 110 volt (Lincolin) MIG welder because we mostly do TIG. In my limited practice with MIG, I've found that "pulsing" like that allows more time for the heat to soak in to the part, giving better penetration without dumping a load of filler. Otherwise the bead would not tie in as it should.
Cold starts occur when the machine is set for best perfomance under steady state conditions (like after you have been welding for a second or two), so in the begining of the weld there won't be enough heat. Using a stop-start technique allows you to set the machine a little hotter and get "good" starts every time.

The drawback is that the impurities that would normally float to the top are now forming holes in the middle of the weld.

In my case I would use this technique to compensate for not having the proper equipment. For structuarlly critical welds it is questionable.

But as I said before, I have very limited experince with MIG, so feel free to correct me.

[dyn88]

try it and buy a cheap dye pen kit, then test it and see, you will find that some people do this well and some poorly. Im curios to know if ANDY dye pens all the welds on their chassis. The best meathod comes with practice, practice, practice, oh and cleanliness(always comes first). Use a wire brush and solvent before performing any criticle(nice spelling huh) welds(especially on load bearing components)

[Paul Seaman]

Dyn88:
Great point the dye pens are peace of mind insurance!