Mig welding tack

[Kirkski]

Does anyone have any insight to why my tack welds seem to have a hole in them?

It's annoying

[Bob W]

Contamination. Not enough shielding gas, dirty metal?

[1955CJ-5]

I agree with Bob....

Clean the area thoroughly..I even used denatured alcohol to remove grease/oil etc...

Are you purging the gas supply line before starting to weld?

If you are filling holes or if the tack holes go through both pieces of metal you need to "back" the opening with copper( a flattened piece of copper pipe works great) or aluminum. This prevents air/oxygen from reaching the weld from behind.

[Roger]

That looks like some of my welds when I forget to turn on my gas bottle.

But as mentioned before... contaminants from the backside may be causing grief.

[Kirkski]

Bob W, Rodger Thank you for the advice, I thought I only needed "backing" when I had a larger gap... I will try this out Friday, thank you so much!

Kirk

[JeepFever]

I am far from expert,� but as others have mentioned,� my first thought was lack of shielding gas.

edit:  just realized this thread is kinda old.    . . did you figure it out?

[Kirkski]

 I posted this on my build page, but should be here as well, since I did start this thread about it...

When I started this project I had no welding experience with MIG. I thought all of the issue I was having was me and my technique.

Turns out after burning through a 2 lb roll of wire that my boss got me from "Advanced Auto Parts" my welds looked no better, had little penetration and I had to grind my backside off to make them look decent..

Well, I went to a local welding supply house and I picked up a new roll of the same spec wire size, grade etc... and what a difference it made..

Beautiful welds, nice penetration and easy clean up... Boy did I learn a valuable lesson... Don't buy crappy wire...

[JeepFever]

I saw your post about the crappy wire in your build thread,  and did not tie the two together.  haha

Speaking of wire,   that got me thinking,  I have some wire in my welder now that results in a weld that is tough to grind.   I have another roll on the shelf that I think is softer.   (the wire itself is easier to bend). 

I probably should have tried this a long time ago.   haha   . . but,  I still have quite-a-bit of welding to do.   I can save the hi-tensile wire for structural projects.

Only reason I have hesitated so far,  the soft roll is .030,  and the existing is .025.  . .   does anyone weld sheetmetal with .030?

[Kirkski]

JeepFever All my welding was .030 wire