Plasma cutting - how much air do I really need?

[jgayman]

I have never owned a Plasma cutter but I plan to get one for home use. How much air flow do I really need? My compressor is a 2.5HP 10 Gal Harbor Freight jobbie. The sticker "says" 5.2 CFM @ 90 PSI. I use it to blow up tires, run some air tools like an impact wrench, air ratchet, etc. It works okay but obviously if I have a lot of bolts to hammer out I will run out of air after a few and have to wait a bit for it to build up.

I have need to occasionally cut anything from sheet metal to 1/2" mild steel. While 95% of the use would be 3/8" and thinner it seems prudent to spend a little extra and get a machine with some extra AMPs that easily handles what I want plus a little. Of course with extra AMPs seems to come additional air flow requirements.

I'm currently looking at something like the Miller 625, Hobart 700i, or Hypertherm PM45. The Miller wants 6 CFM, the Hobart 4.8 CFM, and the Hypertherm 6 CFM.

Is it feasible to run these from my air compressor? Is there an easy way to measure the actual CFM of my compressor?

I really need to stay with a portable type compressor. I don't have room for a larger 220V model.

I appreciate any suggestions from anyone with more experience on these cutters.

 

[Buckgnarly]

I have the Hobart version of the Miller 625, and to be honest it is a bit of an air hog. I have two compressors, a Sears 30 gallon and another big 80 gallon. Both are 220 and both put out somewhere between 9-11 cubc feet at 90psi. When I run the 30 gallon alone I can get about a min or so without the compressor kicking on. Keep in mind you can always wait for the compressor to catch up, just cannot make long continuous cuts.
The cutter is not as bad as a die grinder, but close. If you can run a die grinder decent with your setup, I would say you are fine, otherwise it is time to upgrade the compressor or tank size.

 

[hodge]

I have a Miller 625, and I use a Craftsman 33 gallon upright with 5.1 cfm at 90 psi, and it is all it can do to keep up with the plasma cutter.

 

[gwdixon]

You will need LOTS of air. As soon as you open the torch the air pressure in the system drops dramatically. 5.2 CFM @ 90 PSI is barely enough but when the torch is opened it will drop to 60 psi (or so) and the CFM air delivery will also drop. In summary, it is doubtful that you will have enough air with the current set-up.

The HF compressor probably is rated for the maximum air flow while the plasma cutters are rated for the minimum air flow. Those numbers are too close for comfort. The HF data is probably quite optimistic and gathered with a new machine in an ideal environment.

The only true way to know how much you need is to get the plasma cutter and run the air through the torch. Watch the plasma's air gauge (if so equipped) and if it starts dropping off below the recommended level then you are going to run out of air and cutting efficiency.

You could cut in short bursts and let the compressor catch up but that is a last-ditch solution and will cause poor and uneven cuts.

 

[Shield Arc]

Are you sure you want to go down this path? Once you get the air situation straightened out, then comes the air filter, then the air dryer. Just one thing after the other!

 

[kevin37b]

As far as the cutter definitely get one big enough for your uses . As far as your compressor , you might get away with it a little while . If you are into doing something involving alot of cutting , a big compressor is going to run all the time also . But a bit of patience and good technique, occasional use , you might be okay . The bigger compressors are built to run continuous duty , doubt if your 's will do it very long . The biggest concern with a cutter is keeping moisture out of the air . Very hard on tips . Also , that moisture seperates better as that air cools . Keep 30' or so of air line , or coiled up hose between compressor and water seperator . Those cutters may have built in seperators , but an inline sperator never hurts . Hope this helps .

 

[kevin37b]

Yep , while I was pecking away Shield arc said it all .

 

[jgayman]

I appreciate the feedback.

I have a need to cut metal for small projects and repairs. I have a cold-cut mitre saw that I can use for small pieces of flat stock, angle, etc. I have a small Oxy-Acetyl torch kit that I can use for crude cuts up to 3/8". I was looking for something that would allow for more flexibility when I need to cut something out of a sheet of 1/4" or need to cut odd shapes, etc. In reality I will probably never need to cut thicker than 1/2". I just thought it wise to spend smart and get a unit a bit bigger.

So perhaps I just need to set my sites smaller and stick with something like a Hobart 500i.

Or should I just go with something like a Longevity unit that only needs 4 CFM?

I have no problem with filters and moisture separators.

 

[Buckgnarly]

DO NOT GO SMALL!!!!! Go bigger than what you think you will need!!

As for dry air, I have copper lines in my garage with 3 "zig zag" setups with low drains to cool the air. One dryer at the end of the run and another on the machine. Never had an issue with moisture in all sorts of temps (unheated garage).
Get the right plasma (big!) and you will never go back....though it cannot take the place of the oxy for heating and such!

 

[Shield Arc]

I have a small Oxy-Acetyl torch kit that I can use for crude cuts up to 3/8". I was looking for something that would allow for more flexibility when I need to cut something out of a sheet of 1/4" or need to cut odd shapes, etc. In reality I will probably never need to cut thicker than 1/2".

You realize it takes just as much skill with a plasma as it does oxygen & acetylene to get a good cut?