Compressor capacity for sanding

Re: Compressor capacity for sanding

john lucas

You will have to find someone more knowledgeable than me with the numbers. A sander eats up air faster than any other tool, or is at least up there. It needs to be able to maintain 90 PSI for a considerable amount of time. I had one of the HF 30 gallon things and it would run the entire time I was sanding which turned out not to be good for that machine. I got lucky and found a used 80 gallon machine with a 5 horse 2 piston compressor. It keeps up easily with what I do. Machines that size are expensive new.

Re: Compressor capacity for sanding

Pete in Holland MI

Don't get hung up on how many gallon tank a compressor has. That is misleading. You need to study the CFM (cubic feet per minute) of the compressor if you plan on sanding for long periods. 15 seconds here & there are one thing, but depends on how long you plan to sand at a time.

The tank size only dictates how often your compressor will fire up. If your tool usage is greater than the cfm at 90psi output of your compressor, eventually you will be out of air.

First, figure out the CFM consumption of your tool. Figure out how many seconds it will be on during each minute of each hour.

Example:

Say a sander is rated at 9cfm at 90psi.

You estimate sanding 30 seconds for every minute thru the day.

That shows that you need a compressor of at least 4.5 cfm, else you will steadily lose ground, but it will run continuously to do that.

Note that some tools now are rated with a duty cycle (percent time one within a minute). These seem to be 25% on some tools I've seen. This means that if your sander is rated at 9cfm at 90psi at 25% duty cycle, it actually will consume 36 cfm of air turned on for a steady minute!

Air sanders use a LOT of air. Compressed air is expensive. You may be running a 3 to 5 hp motor to run your little air sander.

Pete

Re: Compressor capacity for sanding

Dick Coers

Just match the compressor rating to the sander. I would then get around 25% bigger compressor so it doesn’t run 100% of the time the sander is running.

Re: Compressor capacity for sanding

Dick Coers

Good response Pete. Running the high hp compressor for sanding is the exact reason Mirka and up with the Ceros and Deros sanders.

Re: Compressor capacity for sanding

jorge

Thank you Pete et all,

so now I have a new question for the people that sand with air, what sanders are you using for the inside of a bowl? An for the

outside?

I have 2 which are 3" that I use inside.

Keith Newton

The older is a Sioux Model 5201 and a Chicago Pneumatic CP7200SMini Random OS. That I bought after thinking I'd lost the other. I have run them many hours on a Rolair 1.5 hp, although a little larger would be nice.

A larger pad isn't of much use inside a bowl since it only touches around the edges. If you get a little sander, be sure to get a universal air connector between it and the quick couple, so you don't fight the stiffness of the hose. Also, I tie / clove hitch a piece of t-shirt around the bottom air--out port to absorb the oil.

Pneumatic random orbital sanders

John K Jordan

I use two pneumatic sanders for bowls and platters.

One is the Grex ROS with 2" or 1" sanding disks. It's small and light weight. I have the extension shafts that let me reach things like the bottom of a box. I like this so much I got a second one.

For things that are less sharply curved I use a pneumatic palm ROS with 3" disks. (Got it from Rizza at Woodturner's Wonders.)

I have not done any power sanding with a rotating close quarters drill for years. I far prefer the gentle action from the random orbital sanders. I usually don't run them wide open, but slowly, easy to do by pressing just a little on the Grex trigger and easier with the palm sander since it has a control valve which limits the air supply. I suspect I could add a valve to the air line for the Grex but I haven't tried that yet.

I use a 5hp 60 gallon compressor and it doesn't need to cycle often when working like this.

I use this with finer grits, rarely coarser than 320. After removing tool marks with negative rake scrapers and smoothing with hand scrapers, not much sanding is needed. Sanding by hand is usually enough sufficient but the sanders are less effort.

JKJ

Re: Compressor capacity for sanding

George Balock

Great topic. I have a stupid corollary question. I own two compressors. One is a 30 gallon 1.5 hp compressor rated at about 4.5 cfm and a more portable 5(?) gallon Emglo rated at about 3 cfm, both at 90 psi. If I made a manifold to combine their air, could I effectively get over 7 cfm @ 90 psi? What are the experts thoughts?

Yes you can. I've done that numerous times.

Keith Newton

All it takes is a T fitting with two male quick connects and one female.

If the pressure switches are not set at the same level, one may start before the other, but that not a real problem.

Also make sure they are plugged into outlets from different breakers, or it will overload and trip.

Re: Pneumatic random orbital sanders

jorge

Thank you John,

Now I have clearer Idea of what I'll have to get. I've been sanding with the close quarters angled drill since day one, some woods straight from the gouge need little or no sanding, some others with areas that cut smooth and areas that raise the grain, are my nemesis, I scrape with cabinet scrapers and sand afterwards, sometimes this process takes more time than the turning did, I want a time economy.

Re: Compressor capacity for sanding

mikeee12345

Several of the facilities I work at have multiple 2000HP process air compressors that tie into a common header manifold that is used to provide process air for the facility. As the demand for air increases each additional air compressor is brought on line to keep up with demand. Each compressor has a rotary vane discharge valve that modulates how much back pressure or supply air is generated by each compressor. As each additional compressor is brought online, the rotary vane valves throttle back on the running compressors as the additional compressor ramps up in speed and adds air to the header and a computer system balances the loads between all of the air compressors running.

With your application each compressor is running wide open trying to keep up with the demand, it would not make any difference on how they were controlled.

Re: Compressor capacity for sanding

mikeee12345

Several of the facilities I work at have multiple 2000HP process air compressors that tie into a common header manifold that is used to provide process air for the facility. As the demand for air increases each additional air compressor is brought on line to keep up with demand. Each compressor has a rotary vane discharge valve that modulates how much back pressure or supply air is generated by each compressor. As each additional compressor is brought online, the rotary vane valves throttle back on the running compressors as the additional compressor ramps up in speed and adds air to the header and a computer system balances the loads between all of the air compressors running.

With your application each compressor is running wide open trying to keep up with the demand, it would not make any difference on how they were controlled.

Re: Compressor capacity for sanding

Joe Fleming

I can comment on the GREX random orbital sander. It is rated for 8 cfm. I have a 1.5 hp compressor that has a 30 gallon tank. A 1.5 hp motor will put out about 4.5 to 5 cfm of air. I can run my sander for 15 to 20 minutes before the tank drains and I need to let the tank recharge.

However, if I need to power sand for 15 to 20 minutes, then I better practice my turning cuts because that is where my problem is.

Joe

Re: Compressor capacity for sanding

Doug Reynolds

I have the Grex AOS368 air powered 105 degree angled drill. Manual states it's operating pressure is 90 psi and, air consumption is 8 SCFM (whatever that means). I used it for the first time the other day and it seemed to stall a lot and, the compressor was running full time.

My compressor (Craftsman 3 1/2 hp, 25 gallon tank, 120 volts, 35+ years old) puts out 6.8 CFM at 90 psi so, I gather it is not powerful enough for the job.

Is it time to upgrade and, if so, to what size?

I also have the Sioux 8000ES 3/8" Variable Speed Close-Quarters Drill which I really like until I read the horror stories of it getting clogged up with sanding dust and has to be rebuilt. I blow it out with compressed air after every use. This is, however, why I bought the Grex so I wouldn't have to worry about sanding dust.

Some folks suggest buying a Harbor Freight angled drill and consider it a disposable tool. Use it until it quits and, buy another.

I also have tried wet sanding which seems to do a decent job if I have a good surface to begin with.

Any advice?

minimum requirements

John K Jordan

>>>GREX random orbital sander. It is rated for 8 cfm.

As I mentioned, I use the Grex and palm sanders with a fairly healthy air compressor, a 5hp 60gal IR. But these will work on a more limited air supply if you don't run them wide open. I generally use them at a gentle power, limiting the air flow with the palm sander and by just barely pressing the trigger on the Grex. However, I don't know the numbers.

I tested the Grex on a smaller compressor once but didn't use it extensively - if I had some kind of in-line air flow meter it would be easy to check the numbers but yikes, those things are expensive!

If someone who lives in E. TN wants to try the Grex (and the palm sander), stop in for a visit.

JKJ