Help. How do you avoid undercut.

4570Man · Sep 26, 2015

I'm using a miller stick welder with 7018 rods. I can't run anywhere close to the amperage most guys say to run without getting severe undercut. My Grandpa had a buddy who was a certified welder, but sadly he passed away a few years ago. He could run 150 amps on drive shaft tubing, but I can't go over 80 amps. On 3/8 inch steel I have to run about 110 amps. Any help would be much appreciated.

Arc weld · Sep 26, 2015

Can you post some pictures of where your having problems? You don't give enough info to be able to give an answer. Is the welder DC or just AC, what were you welding, etc.

4570Man · Sep 27, 2015

I would be glad to post pictures, but I won't be able to get back in the shop until the first of October. It was my Grandpas welder and I don't know if it is AC or DC.

Shield Arc · Sep 27, 2015

First thing that comes to my mind when dealing with undercut, is rod angle. For a guy who doesn't weld much I'd say check the arc length.

Jorville · Sep 27, 2015

You are not saying what size electrode you are using. 150 amps sounds a little like you are using 5/32 electrode. On DC reverse polarity I usually run 3/32 rod on around 85 amps. 1/8 rod at around 120 amps, flat. Vertical will be less. 1/8 rod vertical around 105 amps. welders will vary on heat. I used a gas drive Hobart once that I had to turn way down because it just ran so hot.
A starting point for amperage for a rod would be 20 to 30 amps for each 32nd of electrode size. Then adjust accordingly.

CNC Dan · Sep 27, 2015

Nevermind what the dial says.

If it' too HOT, turn it DOWN.
If it's too COLD, turn it UP.

If you can't tell if it's too hot or cold, you need motr practice.

One of my old welding text books had an exercise of changing the current by a small amounts untill you couldn't weld, to see how it effected the bead.

harlow89 · Sep 27, 2015

if you are doing any sort of weave I would try pausing on the edges for a split second. if you are just dragging the rod I would try a slower travel speed.

4570Man · Sep 27, 2015

I think the rod is 1/8 inch, but I need to measure it to be sure. I can't run 150 amps. 115 is about as hot as I can do.

Arc weld · Sep 27, 2015

There's just so many things that might be causing the undercut. It could be a combination of things as well. Rod angle, travel speed, arc length, amperage, etc.

muddstopper · Sep 27, 2015

That amp setting on the welder is just a guideline. My old ac/dc tombstone would run 1/8 7018 all day long at 90 amps, One click on the knob would turn the rod red as I welded. My lincoln 250amp stick tig machine I havent found that sweet spot yet.

Billrog · Sep 27, 2015

Once I found where my welders ran best for different sized rod I marked it with a felt pen on each welder mainly because I some times have no need to weld for up to a yr. and would never remember what setting I'd used.

Jorville · Sep 28, 2015

4570Man said:
I think the rod is 1/8 inch, but I need to measure it to be sure. I can't run 150 amps. 115 is about as hot as I can do.

The numbers I gave you above is what I used on a Miller 350 Syncrowave. I have seen that From one Miller welder to the next the amp setting heat is close. I think you are using a 1/8 rod, If you are getting undercut at 115 amps maybe the base metal is too thin. If you tried to run 1/8 inch rod at 150 amps on that Miller you would have excessive splatter, and lots more undercut. That"s if your Miller and the Syncrowave I used have the same temperature at the same amp setting..

4570Man · Sep 28, 2015

I don't try to stick weld anything thinner than 1/4 inch. I have a mig for anything thinner. Ray ( the certified welder ) could run 150 amps on driveshaft tubing which is less than 1/8 thick.

4570Man · Oct 3, 2015

I am welding DC with a 1/8 rod. Here are some some pictures of the Miller and the mig.

I tried welding this weld at 125 amps.

It had pretty bad undercut so I reduced to 115 amps with much better success.,

I still had rod left so I turned the piece over and turned the welder up to 125 amps.

Here are some more of my welds some are better than others.

Whoops I accidentally uploaded the Miller twice in place of the mig and the mig is last.

Shield Arc · Oct 3, 2015

One big problem I see, is inconsistent travel speed. I'll bet you a dollar to a donut your rod angle is off too.

4570Man · Oct 3, 2015

Shield Arc said:
One big problem I see, is inconsistent travel speed. I'll bet you a dollar to a donut your rod angle is off too.

You are right, but I have made a lot of progress since the my first stream of globed metal not even worthy of being called a weld.

Shield Arc · Oct 3, 2015

It takes time. One thing that will be a big help to you, is find someone who can weld, and get some one on one lessons. A few members here have come to my shop, within a couple hours, huge improvements in their welding!

4570Man · Oct 3, 2015

The co owner of a local metal fabrication shop told me mid summer I could come over the end of summer when his business slowed down for some lessons, but summer is over and he hasn't said anything else.

Shield Arc · Oct 3, 2015

One on one instruction makes all the difference in the world. When you're having trouble welding, and the welder stands behind you, reaches around you and grabs your hand and welds for you. It doesn't take long before the light comes on, and you get it!