SCFM (Standard Cubic Feet per Minute - Standard meaning Sea Level, 70 deg F)
only means something coupled with a specified pressure. If a compressor is
rated at 10 SCFM free air (that's 0 pressure), you might only get 6 SCFM at
100 psi, and the tool you want to run requires 8 SCFM at 90 psi. On the
other hand, if your hose is big enough you could probably run a tool
requiring 20 SCFM for a minute or two, depending how big your tank is.
Having enough PSI is rarely a problem, though having a higher PSI gives you
more actual air in your tank so you will take longer to run out. IMHO there
is no call for a two stage compressor in your situation. Primarily what that
does is give a much larger capacity by increasing air pressure to a very
high level, giving a garage with 4 people working in it the ability to all
use their impact wrenches/grinders/spray guns all at the same time for a few
minutes, at which point one or two stop and the compressor catches up. It
essentially increases the effective size of the tank. The rare exception
would be a tool/job that requires very high pressure. However, very few
tools need or can use more than around 90 to 100 PSI, and in fact you should
have a regulator to control that.
I would recommend getting (if you can afford it - oh yeah, Credit Suisse -
never mind <g>) a compressor with 10-20% more capacity than the largest air
hog you anticipate running on a continuous basis, and with a fairly large
tank.
And yes, an "oily" one. First of all, a regular oiled compressor does not
put any oil into the air unless or until it's wearing out. Secondly, most
air tools require oil for longevity and top performance, with the obvious
exception of Spray Guns and Sand Blasters. A commonly recommended procedure
is to put an oiler at the compressor to oil all your tools, and bypass it
and use a separate hose with an oil/water filter on it when painting or
blasting.
HTH,
<dnw>
1972 Midget
1998 Safari
1999 9-3
1964 (Me)
----- Original Message -----
From "Graziano, Michael" <michael.graziano at csfb.com>
> I'd like to purchase an air compressor for the new homestead, and cannot
seem to make a decision. I've gone through the archives (read -> old digest
emails saved on PC), but have yet to come to a decision. But, I do have
specific questions.
>
> Here are the basic assumptions of use:
> 1) basic carpentry equipment (nail gun)
> 2) basic automotive (air ratchet, impact gun, air chisel)
> 3) more advanced automotive (blast cabinet, eventual painting)
>
> That leads to several questions:
>
> 1) How much max PSI should I get? Most units are between 125 and 135
PSI. A few offer 150 PSI. How important is this factor? Should I be
concerned more with scfm?
> 2) What exactly is scfm? I know is has to do with air flow, but what
does the acronym stand for? And how much is enough? From one of the
digests:
> at 90 PSI
> 3/8 in. ratchet 3 scfm
> 1/2 in. impact 4
> air hammer 3.5
> cut off tool 4
> nibbler 4
> 3/8 drill 7
> 6" DA sander 4
> orbital sander 10
> sand blaster 6
> painting 4.5-7
>
> 3) What about oil vs oil free? One stage vs. two stage? I would prefer
to get an oil compressor for longer life, but how will that affect the air
tools? Will I have oil all over the place?
>
> I'm looking at 6.7 scfm unit.
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