Ok, I have some spare cash and I was thinking about getting a few air tools. The more I look, the more confused I get. Can anyone explain what I sould be looking for? I want to drive an Impact wrench, ratchet and dremel.

Here is the commpressor I was interested in. http://www.harborfreight.com/cpi/ctaf/Disp...temnumber=38898 So I need something bigger??

So what is CFM, SCFM, PSI (pounds per sq inch)

 

- I have a basic one like this:



- I have never used a "pancake" style like the one you listed.. but they're basically all the same... it should be fine for what you're trying to do...
- I want to upgrade to one like this, but the one we have has to break first:

 

CFM = cubic feet per minute.

Start with these threads. If you still have questions then ask 'em & someone will answer 'em.

http://forums.s2ki.com/forums/showthread.p...threadid=168444
http://forums.s2ki.com/forums/showthread.p...threadid=165919

 

CFM: cubic feet/minute - measures volume of air delivered
SCFM: standard cubic feet/minute - cfm at some standard, ASME defined set of conditions
psi: pounds/sq. in. - measure of air pressure

Think of it in this oversimplified way: pressure (psi) times volume (SCFM) is proportional to power delivered to the tool.

Most compressors will list CFM or SCFM at 40 and 90 psi. They can deliver less air flow at the higher pressure (the motor/ pump can deliver a fixed amount of power, see statement above). You'll run your air tools at 90 or 100 (unless you're painting), so pay attention to that rating. A bigger tank allows the compressor to fill the tank, shut off, and let you run the tank down from the shutoff pressure to 90 or so before the compressor cuts back in. Thus, a higher maximum pressure means the tank is pumped to a higher pressure and will run your tool longer before the pump has to kick back in. And a bigger tank does the same. A lower 'duty cycle' leads to longer compressor life.

Look at the air tools you want to run, and buy a compressor large enough to drive the one that consumes the most air, typically the die grinder or sander/polisher. (Painting may require even more for a full-size gun, though detail guns consume less.) Keep in mind that you usually use an impact wrench intermittently: that is, you remove 5 lug nuts, then put the impact wrench down while you remove the wheel, etc., allowing a compressor that is only adequate to catch up. Sanders and die grinders are used pretty much continuously, so the compressor must be able to keep up. The tool's air consumption rating may be at a 50% duty cycle, but most of us amatuers sand/grind for a few minutes, then stop to look at what we've done.

All of this assumes you're interested in a compressor for personal use, not for a full time shop. For me, at home, I've got a compressor that's really too small (4 hp/11 gallon/direct drive/oilless), but I can afford to wait on it from time to time. The price was right, and I use it about once a month. When time is money, waiting on a compressor won't fly.

In summary: more CFM @ 90 psi, higher max pressure, and bigger tank are "better", although once you have enough for your needs, anything more is wasted. And 230V is more efficient than 115V, but I wouldn't pay to have the service run for hobby use.

 

Here's the air consumption ratings from an old catalog:

1/2" impact wrench: 4.2 - 5.4 cfm@90
3/8" air ratchet: 4 cfm@90
1/4" die grinder: 3 - 4 cfm@90, but remember you use these continuously
sander/polisher: 8 to 11 cfm, again used continuously

I don't see ratings for spray guns, but if memory serves (less likely with each passing day), I'm thinking a full-size spray gun uses something like 12cfm@40.

My little compressor delivers 5.1@90. It is barely adequate for the impact wrench, irritating when using the air ratchet (used more continuously), and virtually useless with the die grinder. It will run a detail paint gun, but not a full-size one.

The compressor you linked to delivers 4.2@90, so it would be severely taxed by a die grinder, unable to run a sander, and wouldn't paint. You'd probably get tired of the compressor running all the time if using an air ratchet, but could get by with an impact wrench.

 

Good advice here. I have had too small a unit and it was frustrating, but many of the larger ones are really designed for a shop. Here is a quote from one vendor:

"CFM (cubic feet per minute) is the best gauge in determining power," said Landsly. "You should select an air compressor that exceeds the CFM of your most powerful air tool by 1-1

 

Stratocaster,

The harbor freight compressor you have link is designed for use with framing and roofing nail guns. It would be completely inadequate for use with any normal garage air tools (wrench, drill, impact gun, grinder)

This is the air compressor that I have at home. The two main features that I like about it is the higher psi allows longer use of tools before the compressor kicks on and it is very quiet for an air compressor. I've used it in the middle of the night and the neighbors never complain about the noise. Since it has a lower hp motor than some of the other units, it doesn't flow as much SCFM, but the higher psi more than makes up for the lower SCFM rating.

 

this is the air compressor/tank I have. http://www.sears.com/sr/javasr/product.do?...pid=00916556000

it is great for most things (grinders, air ratcheting wrenches, impact wrenches, HVLP spray guns, etc). it also comes with some tools, which is great. only thing I don't like about it is the yellow plastic hose. it doesn't stretch that far. but you can go to harbor freight and buy 50' hose for $10.

don't get that harbor freight one you listed, it definitely doesn't have enough power to run anything for any amount of time because of the small tank and compressor. go ahead and get a good compressor (like the one I listed) otherwise after you find out how weak the one you listed is, you'll spend $300-400 for a good one. so why spend $100 on a crappy one after one use you'll see its not so good and buy a good compressor? just do it right and shell out $300-400 for a good compressor from the start.

 

I have a 6 gallon pancake compressor, used primary for nailing and airing up the tires. I will probably pick up an impact wrench at some point, and it should be fine for occasional use.

The information posted so far is good, but I'll add one other point. Oil-free compressors are significantly louder than the oil lubricated ones, and generally have a shorter life. Most of the cheaper compressors you'll find are going to be oil-free. Neither of these is a very significant issue for a light user, but I thought I'd point them out.

 

[QUOTE]Originally posted by jeffbrig Oil-free compressors are significantly louder than the oil lubricated ones, and generally have a shorter life.