Because the amperage of the plasma cutter is held constant, the voltage must increase if the arc, which acts as a resistor, increases. This is accomplished through measuring the voltage of the plasma arc during the cutting process. To control for variance in the height of stock material, industrial plasma tables must know the spacing between the torch’s nozzle and the top of the material. If the sheets warp upwards during the cutting, then the torch is likely to collide with the metal. Arc Voltage Signal (THC)Ĭutting large sheets can present problems for mechanized cutting because these sheets may not be flat to begin with or may warp as you cut them. An external “arc ok” signal is usually only present on plasma cutters specifically marketed for CNC applications. If the plasma arc fails to fire after the trigger signal, then the controller can pause the cutting operation and wait for the operator to service the torch (replace consumables, check compressed air, etc.). While a trigger signal is a must, an “arc ok” signal, which relays the status of the of the plasma arc (on or off), can save time and material. Because this approach presents an electrical hazard, always opt for a cutter with an external trigger connection. I had to splice into the trigger wires of my cutmaster 40, which can be seen here. Most plasma cutters on the list below have a connector for this signal on the front or back of the power supply but some may require you to splice into wires within the cutter. This trigger signal is the minimum communication required between the controller and the plasma cutter. When using a torch for mechanized cutting, the controller board needs a way to initiate the arc through a digital signal. If the plasma arc fails to establish or extinguishes mid-cut, then you pull the trigger again and restart the cut or replace the worn consumables before trying again. When plasma cutting metal plate by hand you pull the trigger to initiate the arc and let go of the trigger to end the cut. Lotos Supreme LTP5500DCNC with external trigger, 'arc ok', and torch height control signals for mechanized cutting. Low and high frequency plasma cutters can have pilot arcs. This consistency is important in CNC applications because the primary arc is turned on and off many times during to a program to move to separate features.Ī common assumption is that if a plasma cutter has a pilot arc, then it is low frequency. The pilot arc can slice through paint and rust, allowing for a consistent primary arc start. Plasma cutters that support pilot arcs will have a positive connection within the torch that allows for the pilot arc to be ignited even when the torch is not close to the material that will be cut. Pilot ArcĪ pilot arc is a secondary arc that is formed prior to ignition of the main arc that will cut the material. I have compiled a list of plasma cutters below that use this low frequency technology and should work with your DIY plasma cutter build. In my opinion, this is money well spent because in my CNC plasma cutter video I spent a lot of time pulling my hair out trying to get a high frequency plasma cutter to work with my table. Blowback start is a more complex way to initiate the plasma stream, and as a result the torch and consumables cost more. Blowback start plasma cutters produce significantly less EMI and can be used around CNC microcontrollers and electronics that have not been engineered to withstand high levels of electrical noise. Less noisy plasma cutters use a technology known as “blowback' or 'moving' start, where a moveable, spring-loaded electrode and a DC spark start the plasma stream. Proper grounding and an industrial control are needed to avoid erratic behavior of the machine when using a HF plasma cutter. Plasma cutters that rely on a high frequency (HF) AC voltage to start the plasma stream radiate a significant amount of electromagnetic interference (EMI).

Unfortunately, not all plasma cutters are suitable for hobbyist CNC tables. Low Frequency Plasma CuttersĪ high voltage, high frequency AC pulse creates a spark between the nozzle and the workpiece to initate the plasma stream.

Superscribe cnc plasma cutter