Plain answers on choosing and running a plasma cutting system with a machine interface, from power supply and torch choice to air quality, consumable cartridges and safe working.
What is a machine interface port and what is divided arc voltage?
A machine interface (discrete control) port lets the plasma power supply talk to a cutting table or controller. It typically carries the plasma start and stop signal, a divided arc voltage for torch height control, and a transfer signal for table motion.
The real arc voltage is far too high to send out directly, so it is scaled down by a set ratio. Some units have several selectable ratios. Follow the cutting machine manufacturer's values for setup, not just the factory default. Some power supplies also have a serial port for more data. Wiring and settings are a job for someone competent with the equipment.
How does a hand torch differ from a machine torch?
A hand torch is shaped for holding, with a trigger, a torch-lock switch and an angled head. Makers make different head angles: a larger angle for general cutting, and a smaller one that helps with gouging, overhead work and hard-to-reach spots. A machine torch has a straight head and no handle, and is clamped into a cutting table or other mechanised carriage.
Fit a machine torch square to the work, and do not overtighten the mounting bracket, as that can damage the torch. Some systems let you change torches with a quick-disconnect fitting. Check the manual for which torches suit your power supply.
How do I know when the consumable cartridge needs changing?
Many current systems use a single-piece cartridge in place of separate electrode, nozzle and swirl ring. Some detect end of life themselves: the arc stops, the torch light and display show a fault, and a spent cartridge will not restart. Treat that as a firm signal to fit a new one.
Before then, watch for slower cutting, a change in arc sound or colour, more dross or a worse edge. With the system off or the torch locked, look at the nozzle orifice. If it is out of round or notched, or the shield or retaining cap is badly worn, change the cartridge. Cutting from the edge and keeping pilot arc time short help it last.
How do I make sure I order the right consumables?
Check the manual for your system. Makers publish a parts guide listing every cartridge or consumable set for each torch. On systems that use cartridges, they are colour coded by job, such as drag cutting, fine cutting of thin sheet, gouging and mechanised cutting, and the system sets its own mode, current and gas pressure from the cartridge, torch type and lead length.
So choose the cartridge for the task and the torch you are using, and do not mix types between hand and machine work. Do not refit a spent cartridge. If your power supply is older or has a different torch, use the manual's part list rather than guessing.
Does torch lead length matter?
Yes. Longer leads let you place the power supply away from the cutting table or work area. On some systems the lead length is one of the inputs the power supply uses to set current and gas pressure automatically, so use only leads and torches the maker approves for your power supply.
Whatever the length, route the lead flat and without twists or kinks, and keep any bend gentle. A kinked lead can also cause poor cutting. A maximum total lead length is set for each power supply, so check the manual before adding extensions, and avoid crushing or coiling the lead.
What does duty cycle mean for a plasma cutter?
Duty cycle is the share of a ten minute period that the machine can keep the arc on at a stated current without overheating. A system rated at 50 per cent at a given current can cut for about five minutes in ten at that setting.
It is not a simple on-time figure: output current, thickness, ambient temperature and long arc stretching all affect it. It matters most for long cuts and mechanised work. If the machine overheats, the arc stops and a temperature fault shows. Leave it switched on so the fan keeps cooling it, and do not restart until the fault clears. Read the data plate for your own ratings.