I have various air tools and they seem to be ok, then I bought a 3" circular
metal high speed cutter and my compressor couldn't keep up. Every 10 seconds
I have to stop the saw and wait for the compressor to catch up, PITA.

I have a real 2 hp, 230V, 20 gal compressor rated at 7.7 CFM @ 90 PSI but
the cutter is only rated at 5 CFM @ 90 PSI. That doesn't make any sense.
What gives?

I have a real 2 hp, 230V, 20 gal compressor rated at 7.7 CFM @ 90 PSI but
the cutter is only rated at 5 CFM @ 90 PSI. That doesn't make any
sense.
What gives?
Sounds like someone didn't put down the right specs. In my experience
air tools like drills and screwdrivers use from 8 to 10 cfm @90psi.

dennis
in nca

On Sat, 22 Oct 2005 15:53:42 -0700, "Frank"
wrote:

I have various air tools and they seem to be ok, then I bought a 3" circular
metal high speed cutter and my compressor couldn't keep up. Every 10 seconds
I have to stop the saw and wait for the compressor to catch up, PITA.

I have a real 2 hp, 230V, 20 gal compressor rated at 7.7 CFM @ 90 PSI but
the cutter is only rated at 5 CFM @ 90 PSI. That doesn't make any sense.
What gives?


It's real simple. The air tool is rated at 1/10 duty cycle. :-)

As for how much air is enough well that depends on what you're
doing. There never seems to be enough air till you go really
overboard. To see my solution look on my home page below and look
under "portable air compressor".


Wayne Cook
Shamrock, TX
http://members.dslextreme.com/users/waynecook/index.htm

"Frank" wrote in
:

I have various air tools and they seem to be ok, then I bought a 3"
circular metal high speed cutter and my compressor couldn't keep up.
Every 10 seconds I have to stop the saw and wait for the compressor to
catch up, PITA.

I have a real 2 hp, 230V, 20 gal compressor rated at 7.7 CFM @ 90 PSI
but the cutter is only rated at 5 CFM @ 90 PSI. That doesn't make any
sense. What gives?




Losses in the air motor. While rated at 5 cfm, that is probably under
absolute ideal conditions on a hand-built prototype saw.
Make sure you use a good air tool oil, like Blaster, which will help with
some of the losses. Generally, like a new auto motor, it takes a bit
before the air blades in the motor 'wear in' and once that has occurred,
it should reduce air consumption some.
I would suggest a bigger tank, 20 gal isn't much at all when you are
working with air tools.

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

"Anthony" wrote in message
...
"Frank" wrote in
:

I have various air tools and they seem to be ok, then I bought a 3"
circular metal high speed cutter and my compressor couldn't keep up.
Every 10 seconds I have to stop the saw and wait for the compressor to
catch up, PITA.

I would suggest a bigger tank, 20 gal isn't much at all when you are
working with air tools.

A bigger tank will only delay the inevitable. Once you draw the air reserve
in the tank down to the point that the compressor kicks in, you're fighting
a losing battle if the compressor is not able to pump air faster than the
tool is consuming it.

- Michael

Do you have 90 or less PSI on the cutter ? or 125 maybe...

I can believe the tank falling from full to the low start compressor level -
beading off air through the tool.

The compressor should be able to just make it to full but I suspect a leak or
more pressure than 90...

Martin
Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder



Frank wrote:
I have various air tools and they seem to be ok, then I bought a 3" circular
metal high speed cutter and my compressor couldn't keep up. Every 10 seconds
I have to stop the saw and wait for the compressor to catch up, PITA.

I have a real 2 hp, 230V, 20 gal compressor rated at 7.7 CFM @ 90 PSI but
the cutter is only rated at 5 CFM @ 90 PSI. That doesn't make any sense.
What gives?



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"Frank" wrote in message
. ..
I have various air tools and they seem to be ok, then I bought a 3"
circular metal high speed cutter and my compressor couldn't keep up. Every
10 seconds I have to stop the saw and wait for the compressor to catch up,
PITA.

I have a real 2 hp, 230V, 20 gal compressor rated at 7.7 CFM @ 90 PSI but
the cutter is only rated at 5 CFM @ 90 PSI. That doesn't make any sense.
What gives?


My bet is it is not really 5 CFM! Many manufacturers are rating their tools
at duty cycle, in other words maybe 25-30% of actual use. My bet is the tool
uses close to 15 CFM continuous.
A 2 HP compressor will not keep up with any air tool I am aware of! Trust me
I had one for years! I upgraded to a compressor that produces about 10 CFM
an it pretty much keeps up with all my tools. 15 CFM would be better, but I
don't work that hard any way!
Greg

"DeepDiver" wrote in
:


A bigger tank will only delay the inevitable. Once you draw the air
reserve in the tank down to the point that the compressor kicks in,
you're fighting a losing battle if the compressor is not able to pump
air faster than the tool is consuming it.


Yup, 100% agree, however, a larger tank will give you more run time
between tank refills, so you can get a bit more work done before the saw
quits.


--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

"Anthony" wrote in message
...
"DeepDiver" wrote in
:

A bigger tank will only delay the inevitable. Once you draw the air
reserve in the tank down to the point that the compressor kicks in,
you're fighting a losing battle if the compressor is not able to pump
air faster than the tool is consuming it.


Yup, 100% agree, however, a larger tank will give you more run time
between tank refills, so you can get a bit more work done before the saw
quits.

Yes, but then you will also have to wait longer for the tank to come back up
to full pressure. The bottom line is that compressor capacity is much more
relevant than tank capacity when it comes to high-volume continuous
operation.

- Michael

With that fairly decent compressor, you deserve a reasonable sized
tank, say 40 gal+ Otherwise the compressor could be compressing air
but not have anywhere to store it. The shop compressor we have is 208
v 3 ph 5+ hp sitting on a 200 gal tank, ~150 psi. Probably upwards of
30 CFM. Even with 2 people blasting away with die grinders
continuously, it only turns on for about 30 sec every 5 minutes. The
cut off tool like the one you describe does uses a fair bit of air
(more than the die grinders), but we have had 2 people with impact guns
simultaneously and it doesn't seem to need to catch ip.

"Martin H. Eastburn" wrote in message
...
Do you have 90 or less PSI on the cutter ? or 125 maybe...

Hmmm. That just triggered an idea. If the tool is rated at 90 PSI and
your compressor is supplying something significantly higher than that, a
regulator will give you significantly more run time. Perhaps not enough, but
more. I think I may try this myself.

Vaughn

On Sat, 22 Oct 2005 15:53:42 -0700, "Frank"
wrote:

I have various air tools and they seem to be ok, then I bought a 3" circular
metal high speed cutter and my compressor couldn't keep up. Every 10 seconds
I have to stop the saw and wait for the compressor to catch up, PITA.

I have a real 2 hp, 230V, 20 gal compressor rated at 7.7 CFM @ 90 PSI but
the cutter is only rated at 5 CFM @ 90 PSI. That doesn't make any sense.
What gives?

11 CFM seems to usually be enough for most single user "garage" shops
in intermittent use. 7.7 CFM is not enough for most rotary air
tools. I doubt that your compressor delivers 7.7 CFM once it gets
hot, particularly if it is a single-stage unit. Further, with a
small tank you'll be delivering hotter air to the tool. Hotter air at
given pressure has less "poosh". Air tools are rated at cited
pressure and flow with supply air at standard temp, probably 20C or
so. Your air won't feel hot from a blowgun because it cools on
expansion. Some rotary air tools get quite cold in operation when
run from supply air at std temp.

A larger tank cools the air more between compression and delivery.
It doesn't increase the capacity of the pump, but if the pump can keep
up it delivers "better" air to the tool. As the air in the tank
cools, pressure drops and the pump adds more air to maintain pressure.

For serious (e.g. professional) use, at least 15 CFM, 18 is
bettter.