TIG weld undercutting?

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I am struggling with fillet welds on 0.040 inch (1 mm) thick copper.   I had been using 1/16" (1.6 mm) TIG rods, deoxidized copper, starting to experiment with 0.045 wire.  (It is a pain to straighten a spool of wire, but can be done with the help of a drill).  I usually use pulse, and sometimes walk the cup.   I consistently have trouble with undercutting, usually on the vertical side.   Why do I only see it on one side?I am using test coupons of 1 inch by 4 inches.   I melt the outside of the corner without adding rod, and then I go back and put in a fillet weld.  Sometimes I try to do it without adding wire, sometimes I add wire.  The purpose of the fillet is for appearance; this is an art piece, so strength is not a concern.   The undercut is significant, and really mars the appearance.   I sometimes see undercut on the outside; however, the appearance there is not as critical as on the outside.   I have been working on process improvement, including measuring tungsten stickout.   However, many hours of practice do not seem to result in improved results.   I have made arrangements to have a private welding lesson from a young man who was recommended to me by a local welding shop; perhaps he will find something that I am doing wrong.I don't consider myself a great welder; I do not weld every day. I have been welding for many years, usually TIG welding.  I believe that welding copper is a lot like welding aluminum, but somewhat more difficult, as copper is more conductive.Looking for suggestions.  Thanks in advance.Richardhttp://www.fergusonsculpture.com
Reply:

Originally Posted by richardferguson

I am struggling with fillet welds on 0.040 inch (1 mm) thick copper.   I had been using 1/16" (1.6 mm) TIG rods, deoxidized copper, starting to experiment with 0.045 wire.  (It is a pain to straighten a spool of wire, but can be done with the help of a drill).  I usually use pulse, and sometimes walk the cup.   I consistently have trouble with undercutting, usually on the vertical side.   Why do I only see it on one side?I am using test coupons of 1 inch by 4 inches.   I melt the outside of the corner without adding rod, and then I go back and put in a fillet weld.  Sometimes I try to do it without adding wire, sometimes I add wire.  The purpose of the fillet is for appearance; this is an art piece, so strength is not a concern.   The undercut is significant, and really mars the appearance.   I sometimes see undercut on the outside; however, the appearance there is not as critical as on the outside.   I have been working on process improvement, including measuring tungsten stickout.   However, many hours of practice do not seem to result in improved results.   I have made arrangements to have a private welding lesson from a young man who was recommended to me by a local welding shop; perhaps he will find something that I am doing wrong.I don't consider myself a great welder; I do not weld every day. I have been welding for many years, usually TIG welding.  I believe that welding copper is a lot like welding aluminum, but somewhat more difficult, as copper is more conductive.Looking for suggestions.  Thanks in advance.Richard
Reply:I don't think you can do an inside corner without filler and not get undercut. Undercut, in my experience is from too much heat, not shoving in enough filler rod, and maybe wrong torch angle. I would put the torch more on the bottom side (which ever side is down towards the ground) since heat rises. The side with the undercut is likely getting too hot. If both sides are undercut, then you need to add filler.
Reply:I am using straight argon gas.  I am not set up for heliumIt is possible that the undercut on the vertical side is because the flat side is against the welding table, which acts as a heat sink.Richardhttp://www.fergusonsculpture.com
Reply:

Originally Posted by richardferguson

I am using straight argon gas.  I am not set up for heliumIt is possible that the undercut on the vertical side is because the flat side is against the welding table, which acts as a heat sink.Richard
Reply:

Originally Posted by Louie1961

I don't think you can do an inside corner without filler and not get undercut.
Reply:With tig, undercut is mostly underfill as others have said. I differ on the torch angle. The weld pool follows the heat, so I would angle the torch up a bit and add more filler from the top of the bead.