Looking for a air compressor what is important

The most important specification is delivered cfm at 90 psi, which is a common working pressure.
Bigger is better. I built my own head using Harbor Freight two cylinder pump and their biggest 240V electric motor (3 hp) and used my old 60 gall tank, inlet and modified the blow off valve. Total cost about $ 400 incl a new pulley and the adjustable belts. To buy something similar to this setup would be $1200+.

It delivers about 15 cfm at 90 psi which is enough to run any of the cheap tools including my sand blasting cabinet and a big impact gun. Compressor is quiet and runs only some of the time with the big air hog tools like the cheap die grinders. Plumbed it entirely in 1/2" iron pipe for safety (I weld and grind in there as well) and access; with plenty of downruns with drains. Make sure your tank has an easily accessible drain - compressing air heats it up dramatically, which will condense inside the tank......which is not bueno for your tools lifespan.

Anything below 7 cfm will end up running all the time while using most tools; having too much compressor means it will be quiet and not wear out prematurely.

If you are on a budget, I would consider the HF 21 or 29 gallon models, although they are both too small to run a real tool. Don't be fooled by the hp ratings, all that matters is how much air volume at real pressure is available. There are plenty of suppliers out there from Craftsman to Husky that should be able to provide you something decent for under $500. Reality is that you should spend more and get something with large pump and large compressor lines and outlets.

I have a Junn-Air pancake style compressor that I frequently use with my nailers. The first time that I turned it on I thought it was broken, because the light came on and there was no noise (I was in the quieter end of a noisy shop). Then I realized that air was coming out of the tank bleeder. I closed it and the tank pressure began to rise. In a quiet room, it makes about as much noise as a refrigerator. It's only 4 cfm at 90 psi, but it runs one of my nailers quite well at the speed that this old guy drives nails. It's also great to use when I do my power carving demos at trade shows, etc. I use a dentist type carver unit with 1/16" shank dentist bits for this.

In my shop I have an Ingersol Rand 14.5 cfm 5 hp 80 gallon compressor because I very occasionally do spray painting and sand blasting outside the shop. When doing either it is a small scale operation and I use a refrigerated dryer in the line to the tool when doing this because neither can handle even the slightest amount of moisture in the air. I also install a filter called a "toilet paper filter", because the filter element is actually a roll of toilet paper. It's a favorite for automotive paint & body shops. The line from the compressor that goes inside my shop has a line filter and regulator in the shop, but does not go through the refrigerated dryer. I use so little air inside the shop that I've never had moist air problems in the shop air.

The tank drain was an automatic unit that purged the condensate every time the compressor shut off, but I went through three of these and all began leaking badly in only a few months of use. I ended up just piping the drain into a 3" X 12" galvanized pipe nipple with a series of bushings at each end to go from 1/2" - 3" and then on the output end from 3" to 1/2", forming a cheap and heavy duty reservoir tank for the condensate, so the condensate builds up in this tank instead of in my compressor tank. On the outlet I added a ball valve and then several sections of 1/2" pipe and elbows to route this drain out through the side of my compressor shed and down toward the ground. Whenever I happen to go into the compressor shed, or more often when I'm sand blasting or spray painting, I just open the ball valve and vent the condensate for a few seconds. The air blast usually scares the geese on the lake as well as the neighbor's dog, but otherwise it works well. No more leaky valves, it works very well, and there's no condensate in my compressor tank to rust it. I shut off the power to this compressor when I leave the shop, but never bleed off the pressure, unless I need to do repairs. I can be away from my shop for 3 or 4 days and when I return there is still 90-100 psi in the tank. I think it's safer to leave the tank at pressure than to bleed it off after each use and then fill it back up and re-stress it the next time that it's needed, as long as the system has no serious air leaks.

Charley

Gary Wiant said:

Thanks everyone for the advice. As for air tools the only tool I'd really be interested in right now is a 5" or 6" orbital sander. I'll check the tool and see what the requirements are for the tool and search accordingly. I am interested in building one of the DIY compressors

Thanks again keep the ideas and recommendations coming

Thanks
Gary

Click to expand...

Orbital sanders use a lot of air. I had a 5” and gave it away as my 5.5 cfm HC wouldn’t run it for more than 5 seconds .It had a small tank though, but regardless of tank size, it would always be playing catch up . It only gave me about 20 seconds with a drill , which was disappointing.

I never thought about building one, and had no idea that was an option .

Here’s the one I gave away which was pretty much useless unless your running nailers or paint guns .
My next ones going to be a dual stage and be done with it

If you are interested in building your own; here is what I used from HF:

Pump: https://www.harborfreight.com/air-t...-twin-cylinder-air-compressor-pump-67698.html

Motor: https://www.harborfreight.com/3-hp-compressor-duty-motor-68302.html

Belts (it runs a dual belt): https://www.harborfreight.com/vibration-free-link-belt-43771.html

Motor Pulley: 5/8 shaft with 3/16 keyway - I tried several until I slowed the pump down enough for app 1050 pump rpm for greatest efficiency.

Below are some pics. The oil can be changed easily, the link belts allow for super tight belt tension. If I was to do it again, I would put the motor onto a slider with a dual bolt tensioner - if the belts aren't really tight (I mean like 3 ft prybar tight) they will slip and burn. This pump is very serious.

Also, keep in mind a lot of the inexpensive tools require about double the air volume of an expensive precision tool. Staplers and nail guns are easy peasy for most compressors. The worst air hogs are impact guns die grinders and sanders. They will easily utilize double or triple their rated airflow (since these are usually free/no load specs). Once you actually use them, they will choke on any of the small compressors, making for a frustrating and imprecise experience. Also, they can spit out oil (which needs to go into each tool before every use) and condensation, making a mess. Rear and adjustable exhaust ports are nice to have; as is some kind of inline dryer with some water traps. Using iron pipe with slightly angled runs and down pipes with ball valves at the bottom allows you to dump most of the condensation within the piping prior to it hitting the tool.

A small compressor will run all the time, get way hotter than a big one, putting more water into your air stream. The tank should have an easily accessible bottom drain.

I leave my 60 gall filled unless I go away for more than a week, also releasing pressure out of the piping and hoses. One thing I wish I had done was put the compressor into the shed, so it would be out of the way and quieter, altho it is way quieter than the old integrated Sears Craftsman Pro 5 hp head. Run a single large dia pipe into the garage, along with the electric controls and two ball valves so everything can be disconnected and shut down easily.
One or more separate regulators are also advisable, since nailers require lower pressure and you want the highest pressure and volume available at the tank.
I modded the blow off valve to 145 psi from it's original 130. This was done through the adjustable diaphragm and has helped the motor run a little less. All of the parts and connectors etc are super cheap at HF. Dont forget to keep an eye on their sales and coupons, I think I paid $115 for the pump and motor each a couple of years ago. The pipe is in stock in various lengths at HD or Lowes; don't forget to use pipe dope. I should have bought a pipe thread cutter and made my own, but there is over 100 ft of it in my garage, so I went a little nuts.

You can build all the distribution pipe and basically connect any compressor, so you can grow with it. Also, it is possible to run compressors in parallel for improved air volume delivery. Lots of info out there, I would stay away from PEX and plastic style piping - compressed air leak can create a serious problem in a wood shop environment - dust explosion and fire stoker being two that come to mind. All hoses should have an easily accessible ball valve shut off where they connect to the piping, as well as a master air and electrical power shut off.

Lots of info out there on the design and running of piping and how to make it work.
I realize working on cars, and having several dozen air tools, my perspective is different than most on here.........spoiled with real air supply is not a bad thing. Kinda like having a cabinet saw or industrial grade router table, dust collector and band saw.....which I bet most have on here lol.

Hope this helps a bit.