WHAT GOES WRONG
Voltage alters the profile. The bottom bead was welded at recommended settings, the middle 4V higher and the top 4V lower. The low-voltage bead is stringy and has hardly penetrated. The over-voltage bead is wide with no extra penetration.
TORCH DISTANCE Holding the torch too far away (top) will result in a poorly-controlled weld with a lack of gas coverage causing porosity. Holding it too close (middle) will obscure the sight of the puddle, making it hard to control. The bottom weld is correct.
WIRE SPEED The top bead is too slow; the middle is too fast; and the bottom is as recommended. It’s difficult not to compensate by moving the torch at a different speed, so the results are subtle. There’s a clear variation in bead height, however.
TRAVEL SPEED If you move too fast (top), the weld pool won’t have time to melt the base metal. If you move too slowly (middle), the pool will melt in too much, becoming wide and burning through thin metal. The bottom bead was at the correct speed.
Weld successive beads on a steel plate. Alternate between push and pull, and left and right hands (this ambidextrousness will be handy for real-world work). Clean out the torch nozzle regularly to prevent a build-up of spatter.