It's probably just me. I can't seem to be able to MIG plug weld a 1/4" hole consistently. Sure, I can get a few of them really well, and some of them passable, but a fair number will strike to the wall of the hole and fill up before filling up, never ever welding to the (in this case) frame tube. I won't even think about welding hundreds of 3/16" dia holes.
Consider a 16 ga piece of steel with a 1/4" hole. That is 1/16" deep and only 1/8 inch from the center of the hole to the hole wall. If you are off center when you pull the trigger by about 1/16" of more, the arc will go to the hole wall rather than the bottom of the hole. Add to that you are usually attacking the weld with the torch at an angle which adds elevation to the centering problem. I'm just not that good.
If possible, I try for 5/16 dia holes. I can start welding at the edge, cross the hole to the other side and finish with 1 circle loop around the diameter.
Maybe if I get more practice time on my new TIG I would try the 3/16 holes
YMMV.
_________________
Chuck.
“Any suspension will work if you don’t let it.” - Colin Chapman
Visit my ongoing MGB Rustoration log:
over HEREOr my Wankel powered Locost log :
over HEREAnd don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766