[Mike926443]

Hey everybody, this is my first post and I'm glad to be here. I noticed something in my mig welds the other day. At the end of them I noticed a little pinhole reohnt in the center of the crater. It only happened on a few of my welds. I was weldinging 1/8" wall thickness rect. tubing to 3/16" plate and I was well over the recommended settings. Probably by about 1.3 volts and 50 wfs. I didn't clean the millscale off as well. I thought that that may have been the case or that I was too hot. I'm not for sure though so if somebody would explain I would greatly appreciate it. Thank you again

[Coldman]

You need to "button off" your end crater to avoid cracking.
When you finish your weld keep your gun in position for a second or so to allow some solidification then fill the crater with a quick blat. This is good practice with all mig work.

[Mike926443]

Ok cool, thank you for the response. What is the cause of this though?

[Coldman]

Shrinkage. Where you finish the puddle draws downwards as it cools and shrinks forming a crater and in your case a pin hole.

[Otto Nobedder]

Coldman is 100% right on this... I meant to reply on buttoning off, but my duties interfered.

On a heavy section, weld of 5/16 or greater, I'll button off twice. The first, I'll stop only maybe half a second and add filler, then a second later hit it again. You want NO crater at the finish, as that's where cracks start. Your pinhole is the point of origin for a cracked weld.

Steve S