Undercutting issues

[gearhead69]

I solely TIG at my job and last week I was basically doing a 90-degree weld of plate onto a piece of tubing where the plate had a hole in it and the tubing went through the hole. The material was stainless. The welds looked okay overall except that I was getting noticeable undercutting on the tubing. The only way I was able to get a significant decrease in it was to change the angle of the torch so that I was coming in almost parallel to the flat plate with the torch at nearly a 90-degree angle to the tubing. It actually lessened the problem a fair amount, but I've noticed that I've had this issue on more than one project at work even on plain steel, and though it's not always a concern with a given job, I'd really like to know what causes it and how I can eliminate it so that when the boss says, "No undercut on this. Period." I can do the job right.

[shovelon]

I think you found your answer. Direct the arc more towards the tube.

[gearhead69]

Is it really all about torch angle? I still saw a small amount of undercutting, but the way the work piece was positioned, I really had nowhere else to go with it. If that's the single determining factor there, then I'm fine with that, but just wondered if there weren't some other things to consider. It seemed like a really weird position to weld in, and I guess maybe I was wondering why the tubing was so sensitive to undercutting from the torch position, whereas the plate didn't seem to be affected much at all.

[spence648]

yes it is about torch angle, ok take a minute and realise whats happening, i imagine the plate was on table and tube was standing straight up at a 90, if your angle was pointing down more towards the plate, arc was cutting into tube, gravity was pulling down on filler and toes never got a chance to fill in. not only gravity pulling on the filler but also your arc force was pushing it down too , I always try to relate torch angle to equally heating up both pieces. work angle and travel angle are very important. hope this helps.

[gearhead69]

Man, you got it right on the money with how the work piece was positioned. The tube was straight up. I am always conscious of how the fill rod flows due to gravity, but didn't think about it at all as far as the parent metal goes. Makes sense to me. I'm going to have more of that work this week starting tomorrow, so I guess I'll have plenty of opportunity to perfect my technique. Thanks.