When operating a CNC Plasma table, it is important to maintain a fixed cutting height of the torch throughout the cutting process in order to achieve good cut quality. While the plasma torch tip-to-plate distance can be automatically set at the start of a cut by the Initial Height Sensing (IHS) switch, it is difficult to maintain this exact height throughout the cut. Remember that a typical plasma cutting torch tip-to-plate distance is only 0.060” and that normal sheet metal and plate stock are not perfectly flat. In addition, the heat generated during the cutting process can cause warpage in the material which makes it even more difficult to maintain this stand-off height. If the torch gets too close to the material during cutting it can cause premature wear to the cutting nozzle and also result in more backside dross. Even worse, the torch can crash into the material if the plate is warped enough over a longer cut which consumes some of the 0.060” starting cut height. Conversely, if the torch pulls too far away from the material it can negatively impact the cut quality and also cause the torch to lose the arc during cutting.
The Torch Height Controller (THC) functions based on the principle that the amount of voltage in the plasma arc between the torch and the material is directly proportional to the length of the plasma arc. In other words, if the torch is closer to the plate the arc voltage will be less than if the torch is further away from the plate assuming all other cutting parameters are equal.
THC is most helpful when cutting thinner metals or cut projects with intricate details. Thin metals are prone to warpage at high heat, and the heat will be more localized to one area of the metal sheet if you’re cutting a lot of detail in a small area. THC helps protect the torch by moving it up if the metal warps close to the nozzle. There will also be an edge quality difference when cutting thicker metals due to the more uniform arc voltage throughout the cut.