How to Build a Plasma Cutter
My background is electronics, 22 years in the U.S. Navy as a Cryptologic Technician and then working as a Canon high end copier technician. A plasma cutting system consists of:
1. Power supply
2. Starting circuit
4. Gas supply
The gas supply is the easiest part because there are lots of choices available. If you already have an air compressor then you just need to make sure it supplies enough volume. Plasma cutters use between 4 to 8cfm depending on the current output. The higher power plasma arcs require more CFM. Usually the pressure is between 65 to 90 psi. Don't forget that the air supply needs to be clean, oil free, and dry.
The torch will come from an existing plasma cutter. Making a torch isn't practical. It would be extremely time consuming to make all the parts and the electrode is made of a not so common metal. The type of electrode metal depends on the gas used. Air and nitrogen use the same metal. And one last but not least point about the torch is that the nozzle and electrode are consumable so a ready supply of replacement parts is required.
The starting circuit. This is doable. The starting circuit usually consists of a high frequency source, an oscillator that causes an arc inside the torch nozzle. When the compressed air flows through the arc it is heated to a high temperature and becomes ionized. At this point the gas becomes plasma and will conduct electricity. The arc is transferred from inside the nozzle to the work piece and the high frequency circuit turns off. Another type of starting circuit doesn't use high frequency and shorts inside the torch to start the arc. I think that would be a function of the torch itself.
The power supply is a major component of the plasma cutter. It provides current between about 10 amps up to about 100 amps depending on what size monster plasma cutter you want to build. The more current the more it will cost. The output voltage is somewhere between 100 volts dc to about 300 volts dc. A good power supply will be regulated and filtered to provide a good clean output. Cost to build a power supply depends on what parts you use. New parts, used parts, make your own parts. Cost will probably run around $300 more or less depending on what the current requirements are. More current equals more money.
My opinion about building a plasma cutter. Although it is doable and many ingenious craftsmen and workshop inventors have built plasma cutters I make the following suggestions;
1. Buy a new plasma cutter. The new models have vast improvements in starting circuits, electrode and nozzle design, and consumable life over older models.
2. Buy a used plasma cutter. Even the older units will more than likely be better designed and more efficient than a homebuilt plasma cutter.
3. Buy a non working plasma cutter for parts to build your home made plasma cutter. You will get a lot of useable parts and they will be rated for plasma cutter use and conditions.
4. I understand that some folks just get a kick out of building and there is nothing wrong with that. If you are that type of person then more power to you. I know the feeling of pride and accomplishment will be worth the trials and tribulations of the inventors process. Enjoy!