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?

 

[joshuabardwell]

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.

Somebody correct me if I'm wrong, but I was under the impression it was realistically impossible to get more than about 2 HP out of a typical 120v outlet. No? HP and cfm ratings on those little compressors are optimistic.

I have basically the exact same compressor, but with an 8 gallon tank, and only a "2 HP" motor (air-quotes intentional). It is rated at 4.5 cfm at 90 PSI and I have measured it at about 4.2 cfm. If you want to estimate the actual cfm of your compressor, you can follow these steps. They're not the most accurate, but they will get you in the ballpark.

 

[yomax4]

Look at the Thermal Dynamics Cut Master 42. It has Vent to Shield technology that requires only 3.2 cf of air. Still cuts 1/2 and it's 115v / 230v. you can use your comperssor with it. At worst on the other units you can cut a minute, wait a minute etc.

 

[joshuabardwell]

I have a small Oxy-Acetyl torch kit that I can use for crude cuts up to 3/8".

If you have an O/A torch that you already know how to use, I'm not sure why you're looking at plasma, unless you just really want a plasma, in which case more power to you. Especially since you say you can't step up to a 220v compressor right now, I think you're going to have a hard time making plasma work. I don't use O/A myself, but I have seen others produce perfectly nice cuts with it. Sure, it takes some skill, but plasma takes skill too. Maybe your time would be better spent practicing with the O/A torch, and put the thousands of dollars you would put getting set up with plasma into something else?

 

[jgayman]

If you have an O/A torch that you already know how to use, I'm not sure why you're looking at plasma, unless you just really want a plasma,

Let me reset.... I'm not an expert with the torch. I probably should have been more specific. My torch kit is one of the small 10CF/20CF portable units. Again, it meets my needs. Saying I "know how to use it" would be a stretch. I can turn one piece of metal into two. I am sure I can cut just as ugly with Plasma.

I would like to eventually get rid of my torch. I don't like messing with the gas as I really don't have a proper place to store it.

 

[joshuabardwell]

I would like to eventually get rid of my torch. I don't like messing with the gas as I really don't have a proper place to store it.

Got it. Not wanting to deal with the gas is the main reason I don't cut with a torch now. Well, that and the up-front expense of getting set up, but that's similar for O/A vs. plasma.

The Thermal Dynamics plasma looks really exciting if it can run off a small portable 110v compressor.

 

[Buckgnarly]

Plasma allows you to cut anything conductive, not just steel like oxy. I do not cut much Al, but when I do the plasma is nice! There is a pros and cons for both, and f you can swing it both is best....but lots o' $$

 

[jgayman]

The Thermal Dynamics plasma looks really exciting if it can run off a small portable 110v compressor.

Yes, the Cutmaster 42 looks nice and at 3.2 CFM should work with a smaller compressor.

 

[jgayman]

Plasma allows you to cut anything conductive, not just steel like oxy. I do not cut much Al, but when I do the plasma is nice! There is a pros and cons for both, and f you can swing it both is best....but lots o' $$

Yes! That is the one other thing I forgot to mention. I actually wasn't aware that Oxy/Acetyl had so many limitations when I got it. It has served me well but I'm ready to swap the bottles for an electric cord. I have to keep my unit in an unheated storage shed which is an issue when the weather is cold. I tried using it last weekend and my Acetylene pressure was ZIP.

 

[BukitCase]

When I got my plasma cutter I looked all over the net for reviews - the Hypertherm PM45 was the ONLY one in that size range that I could find ZERO negative comments about, other than price (around $1600) - it's rated for 1/2", but I've seen videos (soon to be verified personally) of cuts over 1". I have a large (21 CFM, 80 gal., 5 REAL horsepower (Baldor motor, 25 amps @ 240 volt) compressor, so it's not starved :=) - I set up a manifold just for that, with a spare outlet in case I want to run another tool. Since this compressor puts out 165 psi, my manifold consists (in order) of a regulator (so I don't blow anything), then this Amazon.com: Astro Pneumatic 2618 Air Control Unit, 120cfm Capacity: Home Improvement as a pre-filter, then this Amazon.com: Motor Guard M-100-KIT 1/2 NPT Clean Air Filter Kit: Home Improvement -

So far, I've only put maybe 10 hours on it total, with NO sign of wear on consumables. As previously mentioned, practice is everything. A cutting guide also helps make you look like you know what you're doing, and weren't "CUI" (cutting under the influence)

The PM45 is made here in the US - the Cutmaster 42 is NOT. Last I checked, the Cutmaster 52 and up were still made here.

Check out several videos of cuts made with the 45 here

Powermax45 handheld plasma cutter | Hypertherm

Bottom line - no buyer's remorse here... Steve

 

[jgayman]

Thanks Steve.

Let me ask a dump question. Is the volume of air only required for the max cut? Example, the PM45 specs say like 6CFM. But if I am only cutting 1/8" or 1/4" can I assume it would need significantly less than 6CFM?