Minimum compressor needs

As I've mentioned in earlier posts, I'm looking to buy a small compressor for misc home use. I want the smallest usable unit I can get.
Besides low demand tasks, I would also like to occasionally use an impact wrench for a seasonal tire rotation and possibly a die grinder for stripping rust on a wrought iron railings. I've seen both tools rated at around 4cfm @ 90psi.
I visited my local Lowes store and saw a DeWalt/Emglo 4 gal machine rated at 4.1cfm @ 90psi. When I mentioned my intended uses to the sales clerk, he laughed. He said I need *at least* a 15 gal tank to run either tool.
What sort of intermittent use, if any, would a 4 gal unit provide? I don't need Mr Goodwrench levels of performance. I'm just a guy in the driveway doing 2 wheels at a time.
Do I truly need 15 gal+ before even considering using an impact wrench or grinder?
Thanks
--
David
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when running. however, that's constant running. it's supposed to not run more than 50% of the time, else you risk burning out the motor. when it's off, it has to run using the stored tank. a 4 gal tank won't run your wrench for very long, and you'll have to stop to let it refill.
an impact wrench isn't a good example. it is usually only used for very short bursts, which is ok to use a small tank for. a grinder will be used for a long time. you don't want to be stopping every 30 seconds for a minute or two to wait for the tank to catch up.
he's right. 15 might be too small for a grinder. i'd probably look at least 30 gal.
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I use old oxygen tanks in series for heavy volume tasks like bead blasting. All oiless compressors will crap out very soon if allowed to get hot i.e. they run a lot. The rings are Teflon and do not last long when hot. Which is exactly what your dinky compressor is going to do when connected to an impact wrench. I installed an new patio cover this summer and used a 1/2 impact wrench to lag in the screws, 5/16 X 4.5 inches long. Even with my extended tank capacity I could only do one screw at a time. I have an 15 gallon tank and I was running 120 psi.
A 4 gallon tank, lets see fill a tire, blow off the bench, brad nailers, and staplers is all that I would try to run.
Check Harbor Freight, I have an friend that bought an 30 gallon unit for about what I paid for my 15 gallon.
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Gallons don't do the work, the output of the compressor does, but you find small output compressors on small tanks.
An impact wrench is really a low air use tool. Generally it runs for a few seconds and you are done with it so the compressor can catch up. Any small pancake 4 gallon compressor will give you enough air to spin lug nuts off the wheels of your car. A die ginder, air drill, air rachet, or random orbit sander will kill you for air use. I have run these tools of a 20 gallon genuine 2 HP compressor but it would not keep up. I have a 60 gallon Porter Cable compressor that almost keeps up with these tools. PC calls it a 7 HP, but it is really a 3 HP unit, runs on 240 volt only. It is close enough to keeping up for me.
I found that in the end I needed two compressors, a portable, that I can drag around, and a large stationary for work in the shop.
You may want to buy a pancake for now, see how it works for you, then buy a statioary compressor for the shop.
Ratings on air tools are the opposite of HP ratings on compressors! Tools often are rated for less than their constant CFM, and compressors are rated for max HP, not running HP. My be that 4 CFM die grinder is over 10 CFM constant. In fact I have a Granger catalog in front of me right now. Their die grinders are rated for a 25% duty cycle, on for 15 seconds, off for 45. The smallest grinder is rated for 3 CFM, but in constant use it will suck up 12 CFM! Some of the grinders are are over 20 CFM! So hook that up to your 4 gallon compressor and see how many seconds it will run! Greg
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Are you trying to save space, or money?
DJA wrote:

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RTFM for the tools you want to use. Listed will be the SCFM requirements. To use the tool at capacity you will need a compressor and tank that can deliver the volume of air required. You might be able to get by with a smaller unit but you will have to wait for the tank to recharge. I run a 6.0 CFM air chisel on my undersized compressor but if I use it for more than short bursts I have to wait for the tank to refill. I think the tools you mentioned have high pressure and flow. The wrench might meet the short burst factor but the grinder is a sustained operation.
Colbyt
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on 12/15/2004 8:51 PM Robert Barr said the following:

I guess the answer is both, but space is the biggest issue.
The other replys seem to reinforce why they make larger compressors. It sounds like a 4 gal unit will drive low demand tools up to a homeowner use of an impact wrench. That's about it.
That's why I asked.
Thanks.
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David
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"DJA" wrote

If all you will be using a grinder for is wrought iron rails, I would be looking at the wire brushes or the discs sold for drills (if you have a drill!)
I have an original Emglo twin which is a 4 gal., it will run a framing nailer if I use 3/8" lines. It will run 2 roofing coil nailers all day long. It will run an impact gun, fill your tires etc. Since it's portable, it's ideal for taking on the job site. The big ole hunky 30 gal I have sure doesn't see the action the little 4 gal does.
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on 12/15/2004 9:10 PM Cooper said the following:

I have used drill attachments but the awkward size and constant kickback is tiring. I thought the smaller angled grinder would be ideal. I still do, but it doesn't sound like something I can use with a small compressor.
The 4 gal unit will still be useful, but I've lowered my expectations.
Thanks
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David
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