CFM - Average and continuous

[xrdad]

Looking at adding some tools to the arsenal, but ran into something I don't quite understand.

There's a random orbit sander I want from Princess Auto (HF for my American brothers), and the box says "4CFM avg, 11 CFM continuous).

The sales guy had no idea.

I'd assume that it will take 11 CFM to run this tool, but why the 4 CFM spec?

Background: I have a Camp/Haus 5HP 26 gal oil lube 2 cyl cast iron running on 110v (could be converted to 220).
The label spec is 5.8CFM at 90 psi.
I'll likely end up doing an upgrade eventually, but the budget is tight and if I can make this work a little longer, it will help. The usage is for hobby only, in my home garage.

Any idea why the tool has 2 specs?

 

[pipsters]

11 CFM is the air it draws while...running. Average CFM takes into account breaks. It's largely an arbitrary number. I run a 1/2" impact which requires about 20 CFM using a 25 gal tank but it depletes it quickly. You simply are using stored air at that point.

I wouldn't buy an air operated random orbital sander to use with a small 110v compressor. Buy an electric one instead.

 

[rlitman]

Just to be clear, 5hp is an impossible number to hit on a 120V 20A circuit. It's really got to be closer to 2 actual hp.
That compressor is not going to make you happy running a DA sander. My last compressor was a "6hp" 220V 60 gallon Craftsman Pro, and it was just barely able to keep up with my Dynabrade.

Oh, and as a general rule, due to better tolerences, quality name brand air tools require less air than import brands to do the same thing. Still, my Dynabrades (it doesn't get much better quality than that) are out of your compressor's league, unless you feel like sanding for 15 seconds, and then waiting for 30. For me, sanding is more of a "continuous" thing, and continuous CFM numbers are all that matter for a sander. Any other numbers are just fraudulent.

 

[kv501]

Get an electric one. Your compressor will thank you.

Look in the manual and somewhere it will say that while the output is technically 5.8 CFM, the duty cycle for that small of a compressor won't allow it. It will tell you that the duty cycle is 100% but that they "don't recommend" using it to that level. That is manual-speak for, "Don't do that or you will notice funny smells and rapidly decreasing output from your compressor."

If you are going to rattle off 24 lug nuts once every 3 months, yes.

If you often run an 11 CFM tool for more than 5 minutes at a crack, you will have a burned-up compressor.

 

[xrdad]

Thanks guys..
That 4 CFM average really threw me. Never seen that before.

I'm trying to build up my tool box, and for the most part my compressor works fine with my mechanic tools (impact, drill, air hammer). But it hates my air ratchet and angle grinder.
The dilemma now is: do I buy a better compressor, or do I just go electric from here on out?
I picked up a 4 1/2" angle grinder the other day... electric. The sander/polisher is available electric, as are most tools. But it seems a shame to have this big air compressor that has such little output. I might try to sell it and move up a notch.. only then, I'm relying on the tag of the new unit for output that may be totally unrealistic?
With a minimal budget in mind, hard to decide where to put the next $ I have and towards what....

 

[MattT]

Average CFM numbers are sucker bait used to sell air tools to folks with 110v compressors.

The dilemma now is: do I buy a better compressor, or do I just go electric from here on out?

I prefer air when someone else is paying for it but have gone mostly electric/cordless for home use. I only do mechanical work though. Sounds like you're tooling up for bodywork though so you'll need air for paint............

 

[kv501]

I have a 33 gallon 120V compressor that suits me fine. That said I don't run high flow air tools with it. I use it for air nailers, impacts (lug nuts), tires, etc. The only thing I use it for that ***** a lot of air is a texture gun once in a very blue moon. I normally don't do huge rooms, so there is some down time between rooms and also to mix mud and refill the gun.

I have the room for a bigger compressor but I don't want to use that room for one. The one I have is nice because it is portable (can't take 240V to most places), and just enough to spin lug nuts and texture. Anything that's going to take more power I get electric. If I had a dedicated compressor shed and some money to burn I might do it.

Remember that if you do sell the existing one you are going to lose the portability.

 

[xrdad]

Matt, you are right..

I'm am getting set up to do "light" body work. It's for my personal junk piles and has more to do with learning how to do it myself, over trying to make a $$ at it.

I do feel I got 'suckered' into buying this compressor, although I did get it over 10 years ago and it's really done everything I've ever asked it to do. It's probably still worth something for the general hobby guy and I think my hobbies are starting to push it's limit and I have to think about getting something better.

I just don't want to get suckered into another 'weak' compressor. If I can't trust the tag, how will I know which one to get?

In the meantime, I think I'll start getting more electric tools. Maybe this way, the compressor I have can stay and the electrics will be enough for me.

 

[Marlin]

Average CFM numbers are sucker bait used to sell air tools to folks with 110v compressors.

Not always. Although it is a calculated value base on speculation of run time, it makes sense for many types of tools, such as, ratchets and impacts that are not continuous use tools. In the case of these tools if the mfg only listed the at load and free speed values many people would think their compressor was not good for anything more than nail guns and bike tires when in reality with proper hose and fittings they run most impacts and ratchets just fine. The problem is this when this rating is applied to a DA sander using the expected run time equivalent to an impact, which it looks like was done on the DA the OP is referring to.

 

[xrdad]

Here's the flyer for a similar tool they had on sale.

Not sure I believe the rating they gave it?

edit: pics too small, sorry. Here's the link:http://www.princessauto.com/pal/product/8145385/Orbital/6"-Air-Palm-Sander

 

[diesel research]

Here's the flyer for a similar tool they had on sale.

Not sure I believe the rating they gave it?

edit: pics too small, sorry. Here's the link:http://www.princessauto.com/pal/product/8145385/Orbital/6"-Air-Palm-Sander

They are rating it for 10 or 15 seconds run time and 45-50 seconds of rest and then counting how much was used over the "whole" minute.

 

[74grabber]

I'm am getting set up to do "light" body work. It's for my personal junk piles and has more to do with learning how to do it myself, over trying to make a $$ at it.

I am in the same situation in trying to do light body work with small air compressor (I have a 240 compressor but currently in rental house for few more months).

My best solution to my problem was a porter cable polisher sander, and a grizzly spray gun. Get a good air filter dryer setup and should be good to go. From what I have read the porter cable (cant remember model number off top of my head) has a very similiar action to the DA sanders.

Also seen good reviews on the ultra low CFM guns from Eastwood, my pocket book was just not deep enough for them learning and maybe use 10 times in my life.

On other hand the porter cable is not cheap but will be used alot more and usefull for alot of different things. I felt worth every penny to put an investment into it.

This is what I came up with from hours of searching on autobody forums, and I am comfortable I made decent purchases for my usage.

 

[rlitman]

My father has two Porter Cable RO sanders. The 5" with the top grip, and the 6" with the barrel grip.
The 5" is underpowered in my opinion, but is a good tool. The 6" is bulky.
I've got a friend with a Bosch 5" RO sander.
Bosch's best RO is a better sander (but their cheapest is not as good). One nice thing about the Bosch, is that the pad doesn't spin when there is no pressure on it (you have to see it to understand).

But they aren't a true substitute for a pneumatic DA. My 6" dynabrade has more power than the barrel grip PC, and your hand sits much lower to the work, which makes it much easier to handle. Also, electric and wet sanding don't mix too well.