Plasma cutter flow rate requirement


I am buying a plasma cutter, and my welding supplier is pushing the Miller 375.
Very light, small machine, but it does cut nicely on 1/4". I wanted to go up to
a Thermal Dynamic 52, with double the cut. It was only about $400 more (about
1400 vs. 1800).
My old Cambell Hausfeld compressor is rated at 5.7 CFM @ 90psi; it is old and
probably has some small leaks with put the CFM number lower.
The 52 has a flow requirement of 6.7 @75psi; if I am doing the math correctly,
this corresponds to (75/90)*6.7 = 5.6, which my compressor can handle.
Is this correct ? Any advice is appreciated.
Reply to
Bart Killam
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1400 vs. 1800).
Advice:
Hypertherm Powermax Harbor Freight refrigerated air dryer New compressor
Reply to
Pete C.
I second the vote for Hypertherm. They are the leader in plasma cutters now. I am trying to sell my Thermal Dynamics Pak38XL so I can buy the new Hypertherm Max30. I don't really need a new plasma cutter, but the Max30 is just so much smaller and more powerful. The Hypertherm Max30 and the Miller 375 Xtreme are very similar, and both use Hypertherm torches, but the Max30 has the newer nicer torch, and comes with a full kit of accessories.
Reply to
Ernie Leimkuhler
I'm with Pete. I have a Powermax 600 and I do CNC with it - have beautiful cut through 1/2" AR 400F. That is hardened to 400 BHN and Abrasion Resistant - the F is even more resistant. The consumables are lower cost when with Powermax (so I read) and the refrigerated air dryer really saves more. It is 220V.
I have a good filter before the air dryer to keep it clean as well. Martin
Pete C. wrote:
1400 vs. 1800).
Reply to
Martin H. Eastburn
1400 vs. 1800).
How much continuious cutting will you be doing? the compressor can catch up between cuts. seems like you're close enough.
I have a Hypertherm Max 70, has to be 10 years old. works great, the newer ones are smaller.
Thank You, Randy
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Reply to
Randy
Just a hobby welder, very short cutting times, typically under a minute, never over five minutes. Mainly concerned about damaging the machine if the flow rate was less than required.
Mainly was wondering if the flow rate computation was correct. Decided on the Hypertherm 45, the spec sheet gives a flow rate, but not a pressure. Need to contact Hypertherm. After spending about $1500, do not want to buy a new compressor. The high flow rate models can get expensive.
Reply to
Bart Killam
I think the real issue is how fast can your tank re-pump up once a low level is tripped. And is the low level above the working pressure ?!
I have a dual cylinder cast iron on a large verticle tank. I drive air tools without problems. I drive my Hypertherm 600 at flow and pressure - and cut without interrupt. My compressor can, upon trip, deliver more than I use and thereby fill the tank back up to high pressure as I continue to cut.
On large sheet cuts and hundreds of inches on the CNC table - it might cycle on a time or two.
Post the tank and preliminary pressure sensing and regulation I have a particle/water filter - then a refrigerator unit - then another filter on my plasma input. I put cold air out the nozzle.
Martin
Randy wrote:
1400 vs. 1800).
Reply to
Martin H. Eastburn
Your calculations are not correct. You don't get to do the derating calc you show. The operative word is STANDARD cubic feet per minute which is measured at atmospheric pressure. The compressor takes in a certain volume, compresses it to whatever pressure so that is the limiting factor. Higher pressures and the compressor cannot output as much air on the exhaust stroke so the CFM goes down working into higher pressures.
Bart Killam wrote:
1400 vs. 1800).
Reply to
RoyJ
Hypertherm will shut down with error lights on the front if the flow is low. My 600 did. I had ice in my refrig unit and it limited flow. Martin
Bart Killam wrote:
Reply to
Martin H. Eastburn
What's that Lassie? You say that Ernie Leimkuhler fell down the old sci.engr.joining.welding mine and will die if we don't mount a rescue by Fri, 12 Jun 2009 00:27:52 -0700:
Third vote for the powermax30 very nice machine.
Reply to
dan
What's that Lassie? You say that Bart Killam fell down the old sci.engr.joining.welding mine and will die if we don't mount a rescue by Fri, 19 Jun 2009 00:54:51 +0000 (UTC):
The machine will shutdown if the pressure gets too low. On my powermax30, the internal regulator is set at 60psi. I don't know what the pressure switch is set at, but you could just lower the pressure until it gives you a low air fault without cutting to find out how low it can go.
Reply to
dan
On short cuts you will be running off the air in the tank, so the pumping capacity of the compressor will not really come into play.
Thank You, Randy
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Reply to
Randy
I called Hypertherm tech support; the PowerMax 45 need a full 6.0 cfm @90psi. Any lower flow rate would result in auto shutoff with error lights on panel.
I looked into compressors in that range. It seems that under 6.0 cfm, compressors are inexpensive; under $300. The next step up was 7-9cfm, with prices at minimum $800. And these are 220V machines, which would require rewiring my garage for 220V/60A.
So while I can afford the powermax 45; the compressor and rewiring job is not affordable right now. One has to be rich to be a hobbyist welder.
Reply to
Bart Killam
Same with blacksmithing: You can make a small fortune -- if you start with a big one.
Reply to
John Husvar
Any lower flow rate
Buy a second smaller compressor and manifold the two together. You'll increase both the storage capacity with the two tanks, as well as the CFM capacity with both compressors running. The only bad part is you also increase the noise level.
Reply to
Pete C.
As has been pointed out previously, your demands on the compressor will be intermittent. I.e., you will draw from the tank & it will catch up while you're paused to reposition the work and/or yourself. If you're not doing CNC, your duty cycle is likely to be quite low.
Even if you find yourself stopped & waiting for the compressor to catch up, you're still getting work done and nothing's been harmed. And it will happen infrequently.
Go for it! Worst case you'll find that you do need a bigger compressor and you'll live with this one while you save up for the new one.
Bob
Reply to
Bob Engelhardt
With a little bit of patience and attention, you can buy a used compressor for much less than the above prices.
The OP can also use a smaller compressor, as long as it has a big enough tank to hold enough air to make his typical cuts. He would just have to wait between recharges. A possibility to consider is to buy a smallish compressor and a extra tank. Tanks cost next to nothing used.
Some things are inevitable, such as getting at least a 5 HP compressor and rewiring a garage for 220. You can postpone them, but in the end it will be necessary.
Ditto on blacksmithing.
i
Reply to
Ignoramus12074
If you have a big tank that will help. If you have several smaller ones all connected it will deliver from the volume while the pump tries to catch up. You have to have them stored with say 100 more pounds of pressure and regulate it down. SO if you have an old one, put in line and as a storage and even pump it to aid in re-pressuring. When you can replace what you have you might want to keep the extra volume, but not pump.
A lot of time you can find various pumps and tanks for sale in estate sales or simply moving. Using the tanks as a storage area will help a lot!
Think of water. If you have two 1/2" inlets and a 3/4" outlet - one won't be able to keep up, but two will match the output. The volumes in the tanks will deliver the flow as they drop in pressure being refilled by one or more of the 1/2" inlets... So if you don't do 100% cutting for many minutes - you might be ok. When you let go of the trigger, the pump starts overtaking...
Consider cutting right angles - cut 2" across one flat and then let go of the trigger. Reposition and cut again.
You won't use it all of the time, it is best to have one rated higher than needed in volume and pressure.
The one I have is a belt driven, double headed cast iron I bought at Home Depot (as I recall) with all green on the front - meaning all air tools can be used.
The low trip is above my Hypertherm 600 trip point and the pump can generate more than I use and fill the tank several times during long cuts. I cut some 1/2" AR400 pre-hard at 8-10"/minute. If it weren't so tense, I could fall asleep.
I cut thin stuff at 200+ in/min and that scares me as the CNC table goes into action!
Martin
Bart Killam wrote:
Any lower flow rate > would result in auto shutoff with error lights on panel. > > I looked into compressors in that range. It seems that under 6.0 cfm, > compressors are inexpensive; under $300. The next step up was 7-9cfm, with prices > at minimum $800. And these are 220V machines, which would require rewiring > my garage for 220V/60A. > > So while I can afford the powermax 45; the compressor and rewiring job is not > affordable right now. One has to be rich to be a hobbyist welder.
Reply to
Martin H. Eastburn
As I mentioned in another post, you don't have to replace the existing compressor, you can supplement it. If the current compressor can do say 4 CFM you only need to parallel it with another that can do 2 CFM or better to get your required 6 CFM to support continuous cutting.
I fired up the CNC plasma table I've been building for the first time this past weekend :) I did my test cuts on 14 ga steel at 150 IPM and it is amazing the time dilation effect that occurs. The gantry moving at 150 IPM during testing seems pretty slow, but that same 150 IPM seems like a rocket when there is a plasma stream going.
Reply to
Pete C.
What kind of table do you have ? I have one and there are groups in Yahoo. I have PlasmaCam myself.
Martin
Pete C. wrote:
Reply to
Martin H. Eastburn

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