Lead-in cuts determine the starting point of your cutting process. The lead-in and lead-out cut length is determined by the material thickness and the contour of the part being cut. Normally, longer lead-in and lead-out cuts are required for thicker material. The lead-in allows the torch to initially pierce the material, then ramp up current, gas, and speed before cutting the desired part or hole.
The lead-in may be very important, but not as important as the lead-out which is about ¼” to ½” long. The lead-out is a straight or curved cut made at the very end of the part or hole which completes the cutting process. If the programmer makes the lead-out too long, the part may fall from the work piece as the torch is still looking for material to cut. As a result, arc stretching will occur damaging the exterior of the nozzle orifice and in turn negatively affecting cut quality.