Full Size CNC Plasma CuttersThe HF type plasma cutting machine uses a high-frequency, high-voltage spark to ionize the air through the torch head and initiate an arc. These do not require the torch to be in contact with the job material when starting, and so are suitable for applications involving computer numerical controlled (CNC) cutting. More basic machines require tip contact (scratch) with the parent metal to start and then gap separation can occur similar to DC type TIG welders. These more basic type cutters are more susceptible to contact tip and shield damage on starting. The Pilot Arc type uses a two cycle approach to producing plasma, avoiding the need for initial contact. First, a high-voltage, low current circuit is used to initialize a very small high-intensity spark within the torch body, thereby generating a small pocket of plasma gas. This is referred to as the pilot arc. The pilot arc has a return electrical path built into the torch head. The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc. Plasma arcs are extremely hot and are in the range of 25,000 °C. Plasma is an effective means of cutting thin and thick materials alike. Hand-held torches can usually cut up to 50 mm thick steel plate, and stronger computer-controlled torches can cut steel up to 150 mm thick. Since plasma cutters produce a very hot and very localized "cone" to cut with, they are extremely useful for cutting sheet metal in curved or angled shapes.