"slicing and dicing the weld reveals the truth ... "
Ever seen a slick downhill mig weld on hot rolled steel?
For thick hot rolled steel, Thats just wrong with a capital R.
Let me be very clear that we are strictly talking about short circuit mig here. ( aka short arc mig)
not spray or pulsed spray mig.
is like falling off a log. It's easy because gravity is your friend and just pulls the welding puddle along like running a bead of caulk. That is probably how we get sayings like: "You can teach a monkey to Mig weld!"
Mig welding downhill on anything thicker than 1/4" will almost certainly not penetrate completely into the corner...the root of the joint. Unless you are welding with spray transfer (but I am guessing that if you are using spray transfer, you already know what I am talking about here.)
Here is a cross section of what happens when you Mig weld downhill on 3/8" hot rolled steel.
severe lack of penetration and barely even nipped thru the mill scale
Poor mig welding technique will make your mig weld pile up in the middle because gravity is pulling downward on the puddle.
So how do you fight back?
With a good Vertical Mig welding technique and a short stickout...that's how.
The upside down V is one of the most effective techniques for vertical mig welding of lap and tee fillet welds.
Sure there are other ways of making a good looking vertical uphill weld, but for ensuring penetration as well as making a good looking uniform weld, the upside down V is a very good way to go.
Here is a sketch of the technique and also a down and dirty youtube video of this Vertical uphill welding technique.
how to mig weld mig welding basics
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mig welding overhead
Mig machine settings and techniques for overhead welding..
A good ground makes mig welding go better.
A short stickout covers a multitude of transgressions...Using too long a stickout makes everything worse....