Plasma cutting - how much air do I really need?

[Blast Chamber]

I have the Powermax30 and I can cut 1/2 steel with good results. Thats way over what it's rated for.

Agreed. I have the Powermax 30 as well and I love the small size and portability. It has done everything I have asked of it, and the 110VAC input makes it easy to take to another location.

For air I run a pair of small, ancient Kellogg compressors that I picked up cheap on Craigslist. Running both of them simultaneously makes up for the low CFM of each. The pumps are cast iron so I expect them to outlive me.

 

[Gary Fowler]

I just kinda smirk to myself everytime I read one of these threads where someone wants to spend several hundred $$$ for a plasma rig because they cant make a decent cut with any oxy acetylene torch or think its cheaper because they dont have to buy gases. Danger of storing compressed gas bottles is less than storing a plastic gasoline container so any fear there is only perceived and not real although just as in storing any flammable product proper precautions should be followed. Please post back your costs for equipment, parts replacement ie tips, nozzles, tungsten electrodes etc, larger air compressor and quality of cut that you get using you new plasma rig compared to what it would have cost you to get your oxy rig upgraded.
If you already have a cutting torch and are only going to be using Carbon Steel, then your money would be better spent in learning how to use the torch you have and investing in some larger bottles and a bottle cart to move them with.

 

[tjflicek]

Or maybe he just wants one. It's his money!

 

[jimcolt]

The rating for a Powermax45 (Hypertherm) is 6 cfm@ 90 psi. The plasma system has an internal pressure switch that will shut down the DC power when the inlet air pressure drops down to about 80 psi. Most compressors cycle from 90 to 120 psi......some as high as 150 or 160 psi. So....with a compressor with a flow (cfm) rating lower than the plasma- will allow you to cut until the compressor cannot maintain the minimum inlet pressure. Depending on the tank size on your compressor you will likely get 20 to 40 seconds of cut time.....then you will have to wait for the compressor to build pressure...then start cutting again. I have used my Powermax45 outside of my shop many times on a small 3.8cfm@90 psi Porter cable compressor (for nail guns, typically). I can get about 30 seconds of cut....which usually is adequate for small jobs...and if it is sheet metal I am cutting....I can cut a couple of hundred inches in 30 seconds.

The big problem with to small of a compressor is that it will run all the time, and will get very hot....as well as add a lot of moisture to the air. Compressors that are not designed for continous duty simply will not last very long. For field or hobby use....a smaller compressor is often adequate. For shop use and or production use....the compressor should be double the requirement (so a Powermax45 should have a compressor with 12 cfm@90 psi flow).....for best results.

A Hypertherm Powermax30 uses about 4.5cfm @90 psi.


Jim Colt Hypertherm

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.

 

[jimcolt]

A horsepower is equal to about 750 watts......since compressors have a lot of friction....lets say closer to 800 watts are actually consumed. A 20 amp 120 volt outlet can provide about 2400 watts......so in reality, under perfect conditions a 3HP electric motor will run on a 20 amp 120 volt circuit.....as long as there was nothing ellse running on it.
Compressor manufactures use a locked rotor rating to advertise horsepower....which is totally useless....but many will buy based on what the spec sheet says. I have seen 6 HP advertised on 120 volt compressors.

Jim Colt

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.

 

[jimcolt]

This may have been true with the first hand held plasma's from 30 years ago.....but today you plug the plasma into an outlet, plug in an air hose, lay the torch right on the plate....pull the trigger. You can guide the torch on a template or straightedge (metal, cardboard, plastic, wood). It takes just a few minutes to get used to the speed. Todays hand plasma's are pretty easy.


Jim Colt

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

 

[Shield Arc]

I tried the dragging technique, but some plates are just too rough to get a good cut, so I use a burning bar, or the CNC table when I can. But sometimes you just have to free hand things.

 

[jgayman]

I just kinda smirk to myself everytime I read one of these threads where someone wants to spend several hundred $$$ for a plasma rig because they cant make a decent cut with any oxy acetylene torch or think its cheaper because they dont have to buy gases.

Guilty as charged! Do not confuse want with need. I'm just a home user. I don't have a farm and I don't have a shop. Right now the torch kit lives in the shed with the lawn mower which makes it next to impossible to use when the weather turns cold and I cringe when the temps are near 100. The plasma can live in the basement with everything else. I don't like using the torch. I've never had any formal training and the only thing I can remember is "A before O or UP you GO". heh

I have a wire welder but only weld 2-3 times a year. Mostly repairs and an occasional fabrication. In most cases I need to cut material first.

Like most home tinkerers / DIYers, for what I have in tools and gadgets I could cover paying someone else to do the work for the next 20 years but it wouldn't be near as much fun or satisfying.

For the amount of usage per month I don't think the cost of consumables would be an issue.

I really appreciate all the input I've gotten here. It has been very helpful. I'm still not sure when I am going to get one. Still need to look around and do my homework.

 

[yomax4]

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

I thought I posted this earlier. I have a PM-45 at home. Works Great, Consumables last good all though you pay the price for that. I use the 45 for a lot of various cutting on all metals. But...If you pull the cover of of yours you will see at least 4 countries of origin on internal parts. Funny how some are from China......USA made?? kind of. Just syain..

 

[Gary Fowler]

This may have been true with the first hand held plasma's from 30 years ago.....but today you plug the plasma into an outlet, plug in an air hose, lay the torch right on the plate....pull the trigger. You can guide the torch on a template or straightedge (metal, cardboard, plastic, wood). It takes just a few minutes to get used to the speed. Todays hand plasma's are pretty easy.


Jim Colt

You can buy or make a little chariot for you cutting torch also so you can just drag (actually roll) it along, use straight edges also, but with any equipment, you need some skill to use it for good cuts and long use of the equipment. Dragging the tip on the metal will mess up the tip if a bit of spark or molten metal pops up on to it requireing expensive replacement parts.