Probably about 0.8 mm when new... Rather less now, and check for pit marks on both sides of the metal after you've cleaned it up, if you can. Pits in the metal mean it tends to dissolve or blow holes as soon as the arc touches it.
Best to cut away pitted metal, back to good stuff if possible.
As already said, wise to practice on something scrap but clean, around 2 - 3 mm to start with, and when you feel confident, work your way progressively down to 1.00 and 0.8 mm. As the metal gets thinner, aids like alloy or copper plates underneath help to take the heat away from the job. You can make 'spoons' out of flattened copper pipe for reaching under wings and taking a bit of heat away, but the metal has to be cleaned both sides, not just on top. Use the 'Thin Metal Technique' to start with, it makes learning much easier, and you will get a result much quicker.
Doing lots of practice, at all angles, is most important before you start work on your car.
Best to cut away pitted metal, back to good stuff if possible.
As already said, wise to practice on something scrap but clean, around 2 - 3 mm to start with, and when you feel confident, work your way progressively down to 1.00 and 0.8 mm. As the metal gets thinner, aids like alloy or copper plates underneath help to take the heat away from the job. You can make 'spoons' out of flattened copper pipe for reaching under wings and taking a bit of heat away, but the metal has to be cleaned both sides, not just on top. Use the 'Thin Metal Technique' to start with, it makes learning much easier, and you will get a result much quicker.
Doing lots of practice, at all angles, is most important before you start work on your car.