Compressor Choices for Pneumatic Sanders

      It takes a lot of air to power air sanders, but many shop owners consider the upgrade worthwhile. Here's extensive advice on compressor choice, with additional tips on setup and operation. September 8, 2007

I'm going to transition from electric to pneumatic orbital sanders. How much do these things really consume on average? I'll need a new compressor and am wondering what I might need for the sanders and the rest of a small shop (widebelt, door clamp, upcut saw). Seems like something around 17 - 20 CFM should do the trick, since not everything will run at the same time?

Forum Responses
(Cabinetmaking Forum)
From contributor A:
My experience says that two sanders and a few other things going in the shop and you really start to see air used. I just installed an Ingersol Rand T-30 and it is doing great - 35CFM with a 35 CFM Hankison dryer to go with it. The dryer is very important or you will be dealing with a lot of water (unless you are in the desert). I found one used for around $1500 - new is about $3500 for the pair.

From contributor B:
Whatever you buy, buy an electronic drain to dump the tank every time the compressor runs. This one thing really keeps a lot of moisture out. We have a 7.5 screw with a dryer, running with a random orbital sander, PTP, bander and spraying glue and lacquer all at the same time. It keeps up, but we kept our old 10hp 80 gallon tank in the manifold and it adds a lot of volume to the shop. So don't go selling the old tank yet.

From contributor C:
You will need about 5hp/orbital sander. I wouldn't buy less than a 10hp for a small shop plus an air drier and a coalescing filter. We started with a 10 then added a second10 then got a 25hp screw, kept one of the 10's as a backup and let its tank serve as a buffer. Still there are times we run real close on air and have had the CNC shut down due to low air. Most tools don't take much air but the CNC router does, and spray guns too, and the worst, the air sanders. Use a loop-piping layout to limit the pressure drop in the lines.

From contributor D:
This is something that always puzzles me. One electric sander = 1/8 HP, maybe. To do the same work with air powered, you are running a 5 hp motor. It's a lot harder to collect dust, and the hose is much more awkward than an electric cord. Why not get Festools instead?

From contributor E:
There is different action with a pneumatic sander. I use both but for sanding between finishes a 3/32 orbit pneumatic cannot be beat. By the way, I have my Festool extractor hooked up to my pneumatic - 5 hole is available with some models - and it works great!

From contributor B:
We have burned up six Porter Cable sander and two Fein sanders over the past three years and still have done nothing to the Dynabrade air sanders except add oil. It is easier on the hands and easier on the pocket book. The sanders that we have burned up don't offset the cost of the compressor and its accessories, but it sure is nice having enough volume to run a shop of our size. The Dynabrade we have is 3/32 cut and leaves an absolute beautiful surface.

From the original questioner:
I have Festools now, a 5" and 6", hooked to vac. They are starting to wear out (I think I'm on the 3rd pad for each and the vibration is increasing), and I'm hearing that pneumatic is faster with as good or better finish. Is this true?

From contributor C:
We've got 8 Dynabrades and they last a long time if you put a little oil in and don't drop them on the concrete. Before we had a refrigerated air drier we had shorter life from all the air tools. Condensation would get in the bearings. They sand faster than the electrics and give a really good finish. For the increase in compressed air cost you are getting speed and finish quality. Don't buy the off brand replacement pads as they will not be the correct weight for balance. The Dynabrade pads run really smoothly.

From contributor D:
There have been several good suggestions made in response to your question. My advice is if a 7.5 hp (2-stage compressor) that produces 25 CFM at 175 PSI (+- 1) will fit the present needs, add an additional 20% to 25% to this for growth.

A 10 HP (not available in single phase) will produce 35 CFM at 175 PSI. 2-stage is important because it normally reflects a heavier duty unit. 2-stage units are normally cast iron pumps and turn slower RPM's to achieve a higher CFM. The pump does not turn as fast so it does not wear out as fast. The stuff you see in Home Depot and Lowes has 3450 and 3750 RPM motors, thus they turn the pumps fast to achieve the higher CFM. Stay away from compressors that have aluminum pumps.

Automatic tank drain and automatic low level oil switch is a must. The compressor is one of the least noticed machines in a shop until it goes down. Anything that can be done to take the guess work out of it is a major plus. An air dryer is a must for just about anything from air tools to finishing equipment. A refrigerated dryer will take your air temperature down to 38 dew point and remove the moisture.

There are 2 kinds of dryers, one for a compressor with an aircooled aftercooler and one without. A aircooled aftercooler is a radiator looking thing that the air goes through when it leaves the compressor before it enters the tank. The compressor flywheel pulls air through it to cool the air temperature down to 100F or lower. Naturally the dryer that must work with the compressor that does not have an aircooled aftercooler will be more expensive due to needing to bring the air temperature down from a higher starting point.

I suggest you buy quality at the start and it will last up to 75,000 hrs if you do regular maintenance such as oil and air filter. Some of the best piston compressors are made by Champion, Ingersoll, Quincy, Sallor Beall. Most of them are freight free if purchased over the internet.

From contributor B:
One of the things I noticed is the difference between the pad on my Fein sander and the pad on the Dynabrades is the thickness. We can really flatten a lot of solid surface quickly with the Fein, not to mention face frames and doors also. The Dynabrade is a lot better to follow up after the wide belt. I would highly recommend always using the manufacturer’s replacement pads also.

I would truly look at a package rotary screw complete with dryer and tank. I went the other way and thankfully someone came by to help. I know the upfront of 5k to 7k seems like a lot, but the down time of a too small compressor has been probably cost us that of the junk and the screw combined.

From contributor C:
If you opt for a screw get one with the upgraded controls so it will shut off the motor after it goes to unload for a short while. Screws have 3 states: loaded (compressing the air), unloaded but the motor is still running, auto off, after the timer runs down with no air demand the motor is shut off. As soon as the tank pressure dips the compressor will restart. Screws generally operate at lower pressures (120psi) but can turn out higher volumes of air. Be sure to get a drier with the new compressor. We made a mistake and bought a Curtis 25hp screw, not good quality!

From contributor B:
To contributor C: Great point.We had a rep in with little experience telling us to run our screw at 150 psi to make up for the shortcoming of volume/storage. If it wasn't for the shut-off control with a pause/cool-off, we would've definitely cooked the screw. We turned it down to 110 psi, regulate the shop main manifold to 98 psi, and hooked our 10hp piston back to the manifold for the storage. What a difference. Cut our running times by two thirds.

We are saving for a new package from Kaiser, Chicago Pneumatic, or Ingersoll-Rand. They are all great quality and proven performers. We had been told numerous times from our machinery sales reps that the true cost of air becomes evident when junk is purchased, and how smoothly the shop can run with efficient equipment. I wish I had listened in the beginning.

From contributor F:
I invested in a 10 hp upright compressor from Eaton Compressor and a matching air dryer. It is very adequate and I run 2 air sanders. I have 1" copper lines around my shop. The key is to buy the Mirka sanders with the Abranet discs. The Mirka sander has a built in vac feature that works better than any downdraft table I have used. The whole sander is less than $300 and the discs last quite a long time since the dust does not build up on the disc. The sanders need about 16 cfm each. This has proven to be a sweet set up. I saved about $4000 on a down draft table.

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