Flame management from your plasma cutter to the metal being cut by hand or on a CNC table will make things very nice or very ugly. Now some people out there that has used a OA torch for a lot of years under stand flame management. They can take that knowledge and apply it to the plasma cutter. Now with people getting into plasma cutting by hand or on a CNC table need to learn flame management a little better.
The best way I can think of to help others understand this is to use a drill bit set standard or metric. To help understand why the plasma cutter uses different size cutting tips ( some call them nozzles, I will use the word tips ) and different air pressures settings to manage the cutting flame. Keep in mind that the plasma cutter cutting tips have a very small orifice hole that the air and flame comes out of. This also relates to the cut kerf and this should help you under stand. Now take these drill bit out and lay them on the table 1/16", 1/8", 3/16". 1/4", 5/16", 3/8", 7/16" and 1/2" or what they are in metric. Next we take the plasma cutting tip size and amp rating and match it with the drill bits 1/16"/20 amp, 1/8"/30 amp, 3/16"/40 amp, 1/4"/50 amp, 5/16"/60 amp, 3/8"/70 amp, 7/16"/80 amp and 1/2"/90 amp, etc. As you can see the orifice hole gets larger for that amp size cutting tip.
Now that you have an idea of orifice hole size to amp rating. You can also see how this affects cut kerf width. An example would be cutting a snow flake out of 18 gauge at 20 amp with an orifice hole size of 0.6mm or about .025 thousands of an inch this will give you a small kerf that will also give you more detail for the item being cut out. Go back to your drill bits and see how that cut would be affected with a 1.1mm/60 amp tip with a .045 thousands of an inch orifice hole and the wider kerf.. Even if you turned the plasma cutter down to 20 amps you still have the same .045" kerf width. Turning the plasma cutter amperage down with out using the right size cutting tip has no affect on the kerf width.
Here is were we get into air pressure settings for the amp rating and thickness of the metal being cut. Some manuals and cut charts give you air pressure setting for amperage needed for the thickness of metal being cut. Here is a chart I came up with that seems to work well if you do not have a cut chart.
This is what I have found to work with most plasma cutter nozzles/tips that most people have in their shops or garages. NOTE: Orifice hole size 1mm = .03937"
20 amp tip - 0.6mm/.025" - 15 to 20 amps - 50 to 55 psi
30 amp tip - 0.8mm/.030" - 21 to 30 amps - 55 to 60 psi
40 amp tip - 0.9mm/.035" - 31 to 40 amps - 60 to 70 psi
50 amp tip - 1.0mm/.040" - 41 to 50 amps - 65 to 75 psi
60 amp tip - 1.1mm/.044" - 51 to 60 amps - 65 to 75 psi
70 amp tip - 1.2mm/.047" - 61 to 70 amps - 75 to 80 psi
80 amp tip - 1.3mm/.051" - 71 to 80 amps - 75 to 80 psi
Or check with your owners manual for settings.
NOTE: Read your manual for the rated input air pressure and SCFM need to operate your plasma cutter. This in most cases is 90 to 120 psi and 5.5 or more SCFM at 90 psi to maintain the needed air flow to the plasma cutter. Then you set your output or cutting pressure to the chart. I recommend a 3/8" ID hose.
If we take the example from above and were cutting 18 gauge using 50 to 55 psi at the 20 amps thing work well. If you set the air pressure to 75 psi the flame is almost to the point of being blown out. The flame is very erratic and not stable. Now back to the example so you had a 60 amp tip, 50 to 55 psi of air and set at 20 amps. You have a flame that is flared out with no real definition or what you would call a hot spot. What is meant by a hot spot in a flame. A flame has different levels of heat. If you look closely you will see that it has different colors to it. The blue/white area is the hottest part that is were most of the cutting heat is for cutting. So you need to get that part of the flame closest to the metal for the fastest and cleanest cuts.
Now we get into cut height. Most manuals and charts use the standard cut height of .060" This works well for most things but at lower amps with less air pressure this may need to be lowered to .045" to get the hottest part of the flame on the metal. If you are using a 80 amp or more plasma cutter and cutting thick metal at max amps and air pressure you may need to raise the cut height to say .080" or more.
There are a lot of plasma cutters on the market. They all do a good job of cutting metal depending on their capabilities. If your plasma cutter has a torch that only has one size cutting tip then you do all your cutting at that orifice hole size no matter what amps your plasma cutter is set at. This is Ok as long as you under stand that it will not give you the finer cuts as a plasma cutter with a torch that has different size cutting tips do..To give you the finer cuts you may be looking for.
I hope this helps some people under stand more about cutting with a plasma cutter by hand or on a CNC table.