What exactly is lead in/lead out

Can someone let me know what exactly lead in/lead out does exactly? I know if your cutting out a font for example and the torch cuts a bit into your font, that the lead has something to do with it. I just don’t know what exactly it does or how you know what to set it to. Thanks in advance

The kerf (cut width) from a moving torch is smaller than the kerf or hole formed by establishing the plasma arc. So if you start a cut and then move the head along the line you’ll get a wider spot of a cut at the start of the line then you have for the rest of the line. It’ll be lollipop shaped (upside down lollipop since we start at the bottom of a cut and push the torch forward).

Lead-in is a way to eliminate the bulge from your cut line. It tells the machine to back away from the line, establish the plasma arc and then move on to the line where it will now cut the whole line while moving which makes the line’s kerf the same along its whole length.

You have options when defining lead-in in terms of how much distance to back off and what angle to enter the line you’re trying to cut. A larger distance makes it more likely your larger plasma arc establishment hole won’t intersect the line. I usually us a lead-in distance of about twice the running kerf.

The shallower the angle you specify, the less likely you will get distortion of the cut as the head turns to join the cut line. A 90 degree angle is harder to turn while moving then a 30 degree angle. This plus the distance and radius (how long a distance the head will travel to make the turn) helps define how smooth the transition is from the establishment hole to the line.

But you don’t just want to make big lead-ins because it might not fit into the part of the shape you’re going to discard. Then the G-code generation will disregard that toolpath.


Thanks for the reply James. So the value that you enter in for your lead-in, is the distance from your starting point of your cut? If your Kerf is .06 and you set your lead-in at .12, theoretically there should be no distortion in your part?

Correct. I usually use 2x the kerf although I’ll sneak it down to .1 for thinner materials sometimes if I need to fit into a small piece.


Awesome! I will mess with that and see if that fixes some of my issues. Thanks again James

Here is a post I did that deal with lead-in/out.