Selecting a plasma cutter
1. Thickness of metal to cut.
2. How fast do you want to cut.
3. Input power requirements.
5. Ease of Use.
Probably the main consideration in selecting a plasma cutter is the thickness of metal you want to cut and how fast you want to cut. This will determine the power output of the plasma cutter and also the input power requirements. A rule of thumb is that it takes about 25amps per 1/4" of thickness. A 25 amp output will cut 1/4", a 50 amp output will cut 1/2", and a 75 amp output will cut 3/4 inch. These are rough approximations because the cut capacity of a plasma cutter also depends on output voltage. The higher the voltage the less current it will take to cut a given thickness. Another important factor for me is ease of use.
Take a look at this YouTube video by Graham Rhoades at the Welders Warehouse.
Here is a chart to give you an idea of the cutting capacity of various rated outputs.
|Output||Rated Cut||Max Cut||Sever||Pierce|
|12 Amps||1/8 inch||3/16 inch||1/4 inch||12 ga|
|27 Amps||5/16 inch||3/8 inch||1/2 inch||3/16 inch|
|40 Amps||1/2 inch||5/8 inch||7/8 inch||1/4 inch|
|55 Amps||7/8 inch||1 inch||1 1/4 inch||3/8 inch|
|80 Amps||7/8 inch||1 1/4 inch||1 1/2 inch||1/2 inch|
|100 Amps||1 1/4 inch||1 1/2 inch||1 3/4 inch||1 inch|
I would use the Rated Cut as a guide. Although a given output plasma cutter will perform a Max Cut the resulting quality will be less than the rated cut and the cut speed will be a lot slower. Something else to keep in mind is that these cut capacity numbers are derived using consumables in like new condition. As consumables wear the cut capacity and cut quality decline and the speed will slow down. So keep extra electrodes and tips on hand.
Input Power. Personally I would stay away from using a plasma cutter or a welder for that matter on 110 VAC. The reason I suggest this is proved by Ohms Law. As the voltage increases the current decreases. A 15 amp plasma cutter output will require an input circuit capable of providing about 26 amps at 120 VAC but just 13 amps at 220 VAC. These numbers are just to give you an idea of why it's best to use the 220 or higher voltage input power. Make sure you have adequate input power available to run your plasma cutter.
There is also a consideration of ease of use. My first plasma cutter was a Miller CutMate. I bought that about seven years ago and it was well suited for cutting gauge and metal up to 1/8 inch. Back then the plasma cutters didn't have all the features of the units that are available now. One day I tried to cut some 1/4 inch plate and had problems. I was irritated with the lack of satisfactory results and went out and bought a big new Hypertherm 1000 plasma cutter. It was much more plasma cutter than I really needed. It sliced through 3/8 inch mild steel like it was butter. My mistake was in giving the small Miller cutter away. The Hypertherm 1000 is not as convenient to use on gauge as the smaller Miller unit was. It turned out that I missed the convenience and ease of use of the small plasma cutter when cutting thinner material. The big cutter will handle gauge and light steel but the torch is larger, the hose is larger and stiffer, it leaves a larger kerf, the nozzel head is larger, everything about the big cutter is just not as easy, and just not as convenient for cutting light steel and gauge as the small cutter. The moral of the story is to match the plasma cutter with the job. Now I am looking to buy another small plasma cutter. It will either be another Miller or a small Hypertherm. This time I will keep the Hypertherm 1000.
Clean, dry, oil free air. Make sure you have enough air volume to run your plasma cutter. A 30 amp output cutter will need 4 to 5cfm @ 90 psi. A 60 amp cutter will need 6 to 7cfm @ 90psi. Smaller compressors with air tank storage will run a larger cutter but at a reduced duty cycle. I have a 60 gallon Craftsman compressor that runs the 60amp Hypertherm 1000 just fine. Of course I only use the plasma cutter for small projects such as cutting 1/4" or 3/8th inch plate up to 48" wide.