I am trying to install a 3 wire welder to a drye outlet. Does the ground wire go to The "L" shaped prong and the ehite and black wire to the angles flat prongs ?

This may be of help How to wire 240 volt outlets That L shaped receptacle is a neutral

The welder is 240VAC? Straight 240 VAC, 3 wire doesn't have a neutral; 2 hots and a ground. 240VAC 4 wire has 2 hots, a neutral and a ground. Is the dryer outlet 3 or 4 wire? If the outlet is 4 wire then the L is neutral but if you are using only a 3 wire supply to the welder, you will still need a 4 connector plug and use the hot white, hot black and a ground. The L connector is left open.

Hello there!
I thank you very much and that information has confirmed what I need to do. My problem stems from the fact that the welder I am trying to wire has a white, black and green wire... the outlet diagrams have a white, black and red wire. I purchased a 3 prong dual voltage (250v 30a / 250v 50a ) plug.. SO... I have wired the green wire to the "L" shaped prong... the neutral on the outlet... I tested the outlet and have 120v on each flat prong inlet ( 240 altogether)...
Nothing is ever easy. The setup for the outlet is in an poorly accessible area of my basement (very old house)some day I will make an extension cord but for now I will remove the dryer vent and run the cord through the wall to plug it in to the receptacle in the basement and weld in the backyard... not perfect but we do what we must... again.. thank you for the info