There’s a rule of thumb that works really well from thin metals up to about a half inch and maybe 3/4″ of an inch. As your metal gets thicker, the rule doesn’t work quite right.
The rule of thumb for working with steel is one amp per 1000s of thickness. This is just a guideline, a basic ballpark, but it gives you somewhere to start. You’ll need to adjust it depending on what position you’re in, what machine you’re using, etc. Your machine may run a little hotter, for instance.
Keep in mind this rule of thumb only works with TIG and stick. It doesn’t work with MIG welding.
A lot of people use 1/8″ plate steel. Kevin Caron shows a piece of 1/8″ steel and says it is .125 on his caliper, so that means you need about 125 amps to start.
Next Kevin shows a big chunk of 1/4″ steel plate, the kind he uses for the base of a sculpture. Quarter inch is .250 thousands thick, so that translates to 250 amps. So you know that’s about what you’re going to get started with. See how that works, then adjust it, depending upon your machine.
Then he shows a chunk of 1/2″ inch plate. That comes out to .500. Do you really need 500 amps to weld it? In a single pass, you might. Again, it depends upon your welder.
How do you know how thick a piece of metal is?
Kevin shows a tape measure that has fractions across the bottom of the tape.
If you want to cut out a step converting fractions to decimals, use a caliper because it reads in decimals. So it’ll tell you exactly what thickness your metal is. Then you can just do the math from there. Just make sure the caliper isn’t displaying in millimeters – that screws up the measurements all together.
Kevin uses a lot of aluminum in his work and that one amp per thousands for steel is not quite right for aluminum. He takes that number and bumps it up. For example, with 1/8″ aluminum plate you get 125 thousands, but with aluminum 125 amps is not quite enough. He goes up to about 135, 140, maybe even 145 amps, depending upon what position he’s in. Aluminum just needs a little more horsepower.
So this is a good rule of thumb to keep in mind that’ll get you in the ballpark of the right welding setting for you.
Kevin is ready to go back to work, but you might want to stick around another moment and see him jiggerin’ his figgerin’ ….