I started my woodworking career with a quarter blade electric sander, quickly transitioned to a random orbit electric disc sander and finally found that I could substantially shorten sanding time with an air palm sander. I settled on a 5 “Dynabrade sander and a Sears 3HP air compressor. It took me less than an hour to realize my mistake: the little compressor I bought couldn’t start to meet the air demands of the pneumatic sander. It would stick around. without air pressure almost immediately and the air sander would slow to the point of being useless, then you would have to wait several minutes for the pressure to build up again to get another minute of sanding.

To make matters worse, I hired three people as sanders, so I’d have to keep three machines running at full speed all day. I did some calculations and found that I would need a ten horsepower air compressor with a large tank to do this. I was lucky to find a used one for not much money, but it required three phase power and a lot. More money was invested for an electrician to connect it to the building’s 208-volt 3-phase power. The big air compressor was so loud it could be heard throughout the building and on the block, but it powered those three sanders from dawn to dusk. The good news is that it paid for itself by saving sanding time very quickly.

Pneumatic sanders are aggressive and efficient. They are lightweight compared to their lesser electric cousins. My sanders accepted them right away and production took off. I was as happy as they were. Soon there was another machine besides the air compressor that required having large amounts of air in the shop: an Onsrud reverse pin router. It was also great to be able to blow the sawdust off the benches and the machine while cleaning the shop at the end of the day. The compressor was also used to spray finishes on the finished furniture.

Years later, I built a smaller woodworking shop in my house that only required one air sander running at a time. For that store, I bought a half-size air compressor and insulated it in a soundproof room in one corner of the store. I ran ¾ “galvanized tubing under the shop floor to three regulators in three different convenient locations. The machine I purchased for that shop was a 5 HP Ingersoll Rand model with an 80 gallon tank. At the 80 PSI required by my sander Dynabrade, the The compressor would produce enough air throughout the day. I must say the compressor was very well built. All I had to do was keep an eye on the oil level in the sight glass. At night, I would turn off the main air valve on the side of the machine, leaving the electricity on, to silence the compressor overnight.

I must assume that, having read this far, you have some interest in using an air compressor to power pneumatic tools in your shop. A 2-stage reciprocating air compressor will most likely meet the needs of a small or medium-sized shop. As a general rule of thumb, a 5 HP air compressor will drive one pneumatic sander, a 7.5 HP machine will drive two, and a 10 HP machine will be needed for three sanders.

The size of the compressor’s air tank is an important consideration – the smaller the tank, the more often the compressor will need to turn on and off. This is difficult for both the compressor motor and pump over time and consumes more electricity. I wouldn’t even consider an air compressor used to power an air sander with a less than 60 gallon tank and would be much more comfortable with an 80 gallon tank.

The type of electrical power required by an air compressor is another consideration. If you have 3-phase power available at your location, that’s fine. Three-phase motors tend to use electricity a little more efficiently than single-phase motors. Large air compressors will require 3-phase power, but the 5 HP models come either way. If you don’t have 3-phase power available, you can make it with a rotary or electronic phase converter like I did in my smaller store. Whether you use single-phase or three-phase power, you will need 230 VAC power for single-phase motors and 208 or 220 VAC for the three-phase variety. Be sure to check the voltage and amperage requirements of any air compressor before purchasing. Electricians can be expensive.

A two-stage compressor pump is a must for a machine of this size. Two-stage machines have two cylinders, one larger than the other. Air is first introduced into the large cylinder where it is partially compressed and sent to the smaller cylinder for final compression in the tank. As air is compressed, heat is produced, so a good machine will always have a built-in finned intercooler.

Compression not only produces heat but squeezes water out of the air that ends up in the tank. Tanks can rust internally over time and if this is not kept under control, the rusty air tank can eventually explode causing tremendous damage and even death. That is why it is vitally important to drain the water tank every day. Most machines are equipped with a drain valve at the lowest point of the tank. If you don’t want to spray water all over the floor below the compressor, you may consider connecting it from the valve to another location, such as under the floor or into a drain. Running water will flow uphill into a sink because compressed air pushes it out of the tank.

You will need at least a regulator and an in-line water trap first. These are inexpensive. A regulator allows you to set the correct air pressure for the tool you will be using (say 80 PSI) instead of tank pressure (say 175 PSI).

The air output of a compressor pump is expressed in standard cubic feet per minute (SCFM) or simply in cubic feet per minute (CFM). Not all 5 HP compressors emit the same volume of air per minute. This is a function of not only the power of the motor, but also the efficiency of the compressor pump that the motor is feeding. The higher the CFM, the less the compressor will have to cycle on and off to meet the demands you are placing on it. A small compressor pump in a huge tank will not produce more air than in a small tank. The only difference will be in the number of times the compressor turns on and off each hour and the time it takes to re-compress the tank each cycle. In the end, you need to pay more attention to SCFM (or CFM) than to engine power or tank size. Airflow is the end product of any compressor and the CFM should be sufficient for the job at hand.

All reciprocating air compressors release oil with the air they compress. When the tank reaches the maximum designed pounds per square inch, a pressure switch will shut off electrical power to the motor. Simultaneously, a certain amount of oily air will be released into the workshop environment. You may see oil build up on the wall behind the compressor and also in the pump and compressor over time. This is not a cause for alarm, but periodic cleaning may be necessary.

Reciprocating (piston-type) air compressors are loud and this is something you should plan for for the sake of yourself, your workers, and others around your location. If silence is an important criterion, you may want to consider spending the extra money on a screw type air compressor. Screw compressors do not have pistons or cylinders. The air is compressed into a turbine by a large metal screw, which rotates at a very high speed. These compressors just purr compared to the alternative type, but they are very expensive. They sound more like a quiet jet engine than a noisy truck engine.

I hope this article has been useful to you. Buying an air compressor for your woodworking shop can be quite an expensive investment when you consider pipes, regulators, hoses, water traps, wiring, and electricians. You will want to buy a machine that is equal to the jobs it will do, but no more than that. Buying the wrong air compressor can be a very costly mistake. My intention in writing this has been to provide you with the knowledge you will need to select the correct one.