Plasma cutter and under-powered compressor

[couch67]

Hello GJ,

This plasma cutter is on sale, and has been on my watch list. I don't do a lot of sheet work, and I have a metal bandsaw, this would get occasional, light use. Mostly thin stuff, 3/16" and less.

https://www.princessauto.com/en/procut-30a-plasma-cutter/product/PA0008784639

My trouble - my compressor is a husky 2 gal 'quiet' model, which delivers 2 scfm @ 90psi (3scfm @40psi). The plasma cutter spec calls for 6 scfm @75psi.

I'm guessing this is a no-go, even for short cuts on light gauge metal? I'm wondering if an extra tank would help with capacity, to lengthen the cut time. Or is the right compressor the only way to go? Wondering if anyone else out there has some experience with this.

 

[Jbullfrog]

You are correct. A plasma cutter requires the right amount of air flow to cut. You could try adding a larger tank, but you still might not get enough flow.

 

[jack stand]

I'd investigate a metal cutting circular saw for breaking down sheets of that thickness.
Plasma cutters have "consumables" that you WILL consume! I'd be concerned about finding these after 4-5 years with a off brand or re branded machine leaving it useless. Milwaukee has a nice saw but it's in the $350 range the last time I checked.

 

[809]

Also consider oxy torch for cutting metal plate.

 

[couch67]

Thanks for the replies. Yeah, for the amount I would use it, I can't really justify upgrading the air compressor on top of an already spendy purchase. The circular saw looks interesting, I will take a closer look at that.

Based on my needs, maybe a simple torch setup is the way to go for now. It would also help with heating up seized parts.

 

[sherlocktk]

Thanks for the replies. Yeah, for the amount I would use it, I can't really justify upgrading the air compressor on top of an already spendy purchase. The circular saw looks interesting, I will take a closer look at that.

Based on my needs, maybe a simple torch setup is the way to go for now. It would also help with heating up seized parts.

A plasma cutter uses about the same amout of air as a common blow gun for your air compressor. You need to maintain ~65psi or so for the plasma to cut effectively. To test it hook up your blow gun, and look at your PSI gauge, once it drops below 65 that is how long you can use your plasma cutter and still be effective. Plasma cuts thinner sheet goods really fast, thicker stuff takes a while.

 

[couch67]

Quick update - after a bit of experimenting (using @sherlocktk 's advice and more googling, (and the plasma cutter was on sale again), I bit the bullet and bought the one in my first post a few weeks ago. I looked at torches but didn't like the thought of renting tanks for such occasional use. Tips and other consumables are needed for the plasma cutter, but they are relatively cheap for this machine and one kit should last me a very long time with my current use.

I did a small project on the weekend, and made several cuts in 18 gauge plate, several cuts were 24". The air compressor kicks on after about 6" of cutting, but was able to maintain enough pressure for a clean cut right to the 24" mark. I should quantify that by taking a video of the pressure gauge while I'm cutting.

I was amazed how quick and clean the cuts are! Obviously this is with relatively thin stock, and will be different with 1/4 plate - but I don't do a lot of thick cutting at the moment, and will be fine with having to wait on the compressor for those rare times.

 

[sherlocktk]

I know on my cnc machine, the plasma does not get pissed off at me until I get below 45 psi (Forgot to turn on the plasma cutter). I always describe a plasma cutter as a 1/4 inch lightsaber that cuts through metal. I would not write off an air storage tank from harbor freight to get some more capacity if you are patient. You can plumb this together without too much work https://www.harborfreight.com/air-t...-tanks/11-gallon-portable-air-tank-65595.html

 

[nadogail]

I once cobbled together an air compressor using empty refrigerant tanks, at the time they could be had for just asking. They won’t make your compressor larger but they will act as a buffer for your thicker cuts.

 

[jonesg]

plasma or no plasma that compressor isn't big enough for much more than tires.
I bought a cheap HF 21 gal compressor for my plasma 12 yrs ago, the plasma cutter blew up 3 yrs ago,
but the compressor is still in use for air tools etc.
I think I actually used the plasma cutter twice.
Still wish I had bought an OA torch.

 

[The Cobbler]

plasma cutters are great . so much nicer than oxy/acet in my opinion
the consumables at Princess Auto are on the pricey side , you can probably do better on Ebay or amazon . I bought some drag tip consumeables & seem to use them more than the regular ones that come with the machine .

 

[Jswain]

All the small tank does is limit your duty cycle basically. Instead of being able to cut for 6 minutes straight maybe you get 30 seconds, but you can cut quite a bit in 30 seconds.

Find yourself a small portable air tank to add some volume to your system when you can. You don't need the biggest and baddest everything to cut a 2" wide piece of 1/8" plate every 10 minutes.

 

[metalmagpie]

When I was doing architectural steel fabrication, I had a plasma cutter on the job site and I used the same air as the framing crew did to run their nail guns. It would run out of air during a cut. Big problem. I made a reserve air tank out of an old 20 lb propane bottle. I'd fill that up and once it was pressurized I'd make my cut. If a bunch of nail guns started firing at the same time, the air draw would come out of the bottle. It worked just fine. All the carpenters realized what I'd done and they came in and asked me about it with their jaws dropped. They couldn't believe a junk BBQ bottle and a few pipe fittings would fix a big plasma cutting problem.

I think I still have that air tank. I use it now mostly if one of my kids gets a flat tire and needs it filled up somewhere in the neighborhood. I fill up the air tank and give it to them. They haul it back to their car and then it's just like an air hose at a gas station.

metalmagpie

 

[ez-duzit]

plasma or no plasma that compressor isn't big enough for much more than tires...

This. Generally you need 10-12 cu ft/min @ 90 psi. In other words, your compressor *****.

 

[couch67]

So, I ended up taking the advice of adding some ballast to the system. 5 gallon portable tanks were half price last week at PA so I bought one. If money and space were not a consideration, I might look at larger compressors - but my testing showed this upgrade will suit my current (and hopefully future) needs.

I also reconfirmed that the compressor specs will allow for longer run times. The manual states the compressor is 'designed for continuous operation', but for long term reliability, should be run up to 30 minutes per hour. No problem from me.

Did some preliminary tests before going too far with more permanent plumbing / fixturing:

All tests were done with an air gun with similar flow rate to plasma cutter, and measured the time to reach various pressure drops (120 to 90psi, and 120 to 70psi). I have another project to start in a few weeks that will get more plasma cutting time - I will see if the results are comparable when using the cutter. 70psi is the minimum recommended operating pressure of my plasma cutter.

Pressure (psi)	Without Portable Tank (seconds)	With Portable Tank (seconds)
120 to 90 (90 is kick on pressure)	9.5	34
120 to 70	35	120

I made up a bracket to hold the tank at the ceiling (out of the way), close to the hose reel. Added another drain as well. This was before painting.

(Note the horizontal pipe in front of the tank isn't part of the air system, it just rests on the garage door tracks and is used to hang things up to dry)



Bracket is painted, and lined with foam leftover from an old yoga mat

 

[isb cornbinder]

You are correct. A plasma cutter requires the right amount of air flow to cut. You could try adding a larger tank, but you still might not get enough flow.

A larger tank will not increase the output of the compressor. What you have may be enough volume because it may be unlikely that you will cut continuously. The compressor can continue to run and supply air to the tank while you are not actively cutting.
I have owned and used a MILLER Spectrum 300 for more than 20 years. This 300 cannot out draw my Ingersoll T30. The T30 may start while I am cutting, build up the pressure then shut off while I am cutting. This could happen in your situation, although more frequently if your compressor output is lower CFM.

 

[nadogail]

A small compressor is comparable to a small paycheck. You can spend large amounts of your money but you will have to do it less often. A bigger storage tank is comparable to a savings account that you make deposits to so you can take those expensive vacations, just a lot less often.

 

[Uncle murph]

A larger tank will not increase the output of the compressor. What you have may be enough volume because it may be unlikely that you will cut continuously. The compressor can continue to run and supply air to the tank while you are not actively cutting.
I have owned and used a MILLER Spectrum 300 for more than 20 years. This 300 cannot out draw my Ingersoll T30. The T30 may start while I am cutting, build up the pressure then shut off while I am cutting. This could happen in your situation, although more frequently if your compressor output is lower CFM.

Very nice!

 

[couch67]

A larger tank will not increase the output of the compressor. What you have may be enough volume because it may be unlikely that you will cut continuously. The compressor can continue to run and supply air to the tank while you are not actively cutting.
I have owned and used a MILLER Spectrum 300 for more than 20 years. This 300 cannot out draw my Ingersoll T30. The T30 may start while I am cutting, build up the pressure then shut off while I am cutting. This could happen in your situation, although more frequently if your compressor output is lower CFM.

Exactly. Compressor output is the same but the air tank just adds some extra buffer. It goes without saying the compressor and tank needs more time to get back to full pressure, given the cfm to replenish is the same and the volume is much larger.

As long as I'm not cutting huge amounts of 1/4" plus material, or start sandblasting, I think the setup will serve me well.

A small compressor is comparable to a small paycheck. You can spend large amounts of your money but you will have to do it less often. A bigger storage tank is comparable to a savings account that you make deposits to so you can take those expensive vacations, just a lot less often.

Agreed! Good analogy. Everyone can relate to money.

 

[ez-duzit]

You are limited by an insufficient compressor.

 

[couch67]

You are limited by an insufficient compressor.

yeah thanks. heard you the first time.

 

[Jswain]

Some people drive to the store in a Civic, and some people drive to the store in a Cadillac.
Rarely do the people driving the Cadillac realize you can drive to the store in a Civic just fine.

 

[Dewaynep]

Wish I had seen this sooner, but you got the gist of what I would've said. I have a miller model 375 (I think that's the model) plasma cutter. I have used it with a very small, very inexpensive pancake compressor that was very worn out to cut up a wood burning stove that was in a friends basement. It worked just fine. You'll be fine, as you have already figured out.