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mini air compressor

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  • mini air compressor

    Well, the adiabatic air compression scheme is out the window now, but I still want to build myself a small air compressor for the toolbox. I am thinking about a radial piston design, pancake type. I'm also considering a single cylinder long stroke type, possibly double acting. Just looking for more ideas- any and all thoughts welcome.

    The space I have to fit this into is about 22 inches in height, 8 inches wide, and 2 inches deep. That pretty much dictates a pancake design, which suits a radial just fine. The space also suits a long cylinder design, provided I can find a way to run a piston up and down the cylinder in a stroke about 5 times the piston diameter without the connecting rod interfering with the cylinder. One thing I don't want is a tiny piston scorching up and down a short cylinder at the speed of light, making more heat than anything else except noise.

    My intended use is for headless pin guns and brad guns. No air drills, or other high CFM usage tools. I fully expect to get only a few shots before the motor has to come on, since the tank is very small also. If the thing has to run constantly to give me one shot every five seconds, that will be fine. The fully charged tank will give me about four shots before needing the pump, and that's within my working envelope.

    I'm probably going to use a 3-400 watt range universal motor to keep the weight down, or maybe a PM motor of suitable size. Small treadmill motor, perhaps. No heavy induction motor- I ain't lugging one of those up and down stairs. The whole idea of this workbox is that I have all my required tools in it, and I don't have to separately tote a portable air compressor. The box is built- I can stand on it, my head just short of the ceiling, and I don't have to bend down to the floor to reach the most used tools and fasteners. If I can keep the total loaded weight to about 45 lbs, that will work. That's 30 lbs for hand tools, a jigsaw, two cordless drills, pin gun and headless pin gun, plus assorted fasteners- and the air system, air hose, extension cord- I'm looking at about 12 lbs or so max for the complete air system. The tank weighs about one lb, the motor about 3 lbs- no suggestions that include cast iron please-
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    Do what I did and use a CO2 tank from a paint pistol and get a regulator for the 3000 psi max pressure. I used this rig to go around for punch list items when I was a finish carpenter. It was so nice not hearing a compressor I got several extra tanks and used this system exclusively for all trim nailing they last a long time even shooting 15ga finish nails.

    I just did a search and these rigs are available commericially now. Lowes has one and Mcfeelys has one . Good luck


    • #3
      Darryl, years ago, Sears Craftsman sold a 3/4 hp compressor. It was a carbon piston in a carbon cylinder sleeve. My grandson presently has one, but the sleeve is worn and pressure is down. My point is, this unit is only the diameter of a 3/4 hp cap. start, 3450 rpm motor, which is about 8" and about 16" long. It should easily drive a pin gun with a small tank and regulator.
      Alternatively, have you considered "reworking" one of those little 12 volt tire inflators from CTC. With a universal motor, it might serve you very well.
      Duffy, Gatineau, Quebec


      • #4
        Hmmm... I'd just go up and down the stairs twice with two or more packages.
        ..but I like the spirit of your as yet dream.
        John M...your (un)usual basement dweller


        • #5
          The 12v tire inflator type of thing is what I'd like to avoid. I'd be building this device myself, and considering it a home shop project, so I don't mind spending the time to come up with something reasonable.

          I like the idea of a much higher pressure bottle with a regulator, though it does require attention to filling, and might also represent a safety problem on the jobsite. I think I'd rather stick to the built-in pump-

          Thanks for the suggestions.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


          • #6
            This comes to mind- I wonder if it's possible to convert an air tool into a pump- say a die grinder or drill- anybody tried driving one with a motor to see if it will work backwards?
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


            • #7
              A little out of the ordinary, but have you considered a 2 cylinder (opposed) compressor layout with a scotch yoke to turn the rotary into linear - no scraping the cylinder sides and the pressure fluctuations would not be as great with 2 cylinders 180 degrees apart. If you had a pancake motor you might even be able to fit that into a 2" height (say 1" bore pistons).



              • #8
                Have you considered using an old weed whacker, or chainsaw and building from there? It would be a fairly small package.

                Edit. just reread you original post, and don't think my idea would fit.
                Last edited by J. Randall; 10-15-2010, 11:20 PM.


                • #9
                  This may be a little bigger than what you were thinking of...

                  Have you considered gutting a cheap pancake compressor and replacing the compressor motor with one from a refrigerator? I've been toying with this idea for a while and I am convinced that it would make a compressor that was small, light weight, and whisper quiet. The obvious drawback is that the recovery time would be longer than normal and maintaining the proper oil level would not be easy without installing some kind of sight gauge.

                  Just a thought.


                  • #10
                    Friend at work said he used to use a refrigerator compressor for his portable air system. One of the smallest ones, like from a 2 cu ft or smaller. I'm kind of leaning away from that because of the smell they make, or used to make anyway. Still that could be a viable way to go.

                    I do like the scotch yoke idea, that had eluded me. Two pistons opposed on the same shaft would lend well to that configuration. That is a likely candidate for my project, thank you.

                    I've had another idea as well, using fluid as a piston. There would be two cylinders vertically, side by side, with a fixed volume of oil in them. A fluid pump would work through a reversing valve to alternately transfer the fluid from one cylinder to the other, compressing the air above the fluid column each time the transfer takes place. A sensing device of some kind would activate the reversing valve. Water would collect in the fluid of course, and would have to be drained as required.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                    • #11
                      I had a sandblasting and painting company. We used huge compressors for the sandblasting. Up to 1600 cubic feet per minute. The older compressors were rotary vane compressors. The new ones were screw compressors. The rotary vane compressors were easily repaired. The screw compressors were much more difficult and expensive to repair. The screw compressors were much quieter.

                      A die grinder uses a rotary vane compressor as does a impact wrench. I don't know if you could use one in reverse to compress air but I think you could. The volume of air produced would have to be calculated. The oil separator would be the biggest issue I would suppose.
                      Location: The Black Forest in Germany

                      How to become a millionaire: Start out with 10 million and take up machining as a hobby!


                      • #12
                        OK. Winging it here. Letting loose the crows of creativity. Compressor. Small. Quiet. Compact.

                        Opposed free piston electro-magnetically driven.

                        The pistons are linearly coded for axial position.

                        A big spring between the pistons recirculates kenetic energy.

                        While the pistons are mass balanced they are two stage and the magnetic drive keeps the pistons on the head end of their stroke (high in any case) making it possible to modulate delivery without sacrificing efficiency.

                        Reed valves: hard to beat them for weight and durability. Keep the moving mass down and they can operate at dazzlng speed.

                        I picture a compresser the size of a quart thermos running about 500Hz with 2 1/2" pistons putting out 3 CFM with 1/2" stroke @ 500 Hz.

                        The pistons are rare earth magnets and the spring tensioned to provide about 1/2 the compresson force relieving some of the work load of the mag driver.

                        The only detial I can't decide is whether to compress on both side of the pistons or the outboard sides.

                        Drive electronics? I haven't a clue. Ingenious would be good.

                        OK I thunk it up; now you guys build it.
                        Last edited by Forrest Addy; 10-16-2010, 04:09 AM.


                        • #13
                          Forrest, I like that idea as well. It would be about as vibration-free as could be. I would think that

                          There was an article written some years ago about solenoid operated valves for an engine. There was a particular type of solenoid that gave a very high 'push' with a fair degree of efficiency, but the stroke would be seriously limited. I'll have to look into that. Maybe a 3 ph drive could be arranged somehow- being an electronical type person I should be able to figure that out. It could be arranged where both pistons are driven towards center, and a single pressure sensor feeds an electronic circuit to control the commutation and drive reversal.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                          • #14
                            Forrest:- do the crows of creativity live in the same zoo as the dogs of war? (The devil MADE me ask!)
                            Duffy, Gatineau, Quebec


                            • #15
                              Seems like the crows of creativity have pecked at my last post. Some of the text I had typed is missing in action- or maybe the dogs of war have eaten it

                              Now I have another question about sealing rings. I have a couple types, one has little side support area, but the other has a substantial 'square' edge to it, with a slight outward lean at the actual sealing lip. Can that square edge be used to offer side support? In other words, do I need to have a substantial length to the piston, or can I get away with basically a disc machined up to fit the seal onto? If I go with a two piston design where both are connected by a shaft, then both are automatically kept square in their bores. There will be some side pressure if I use the yoke design, though I don't know how much. Maybe I should play it safe and use a substantial length for the pistons and just let the rings float.

                              I have some nicely polished tubing from a shock absorber that I'll use for the cylinders, and I'll insert those into machined aluminum heads. The heads will be joined to a front and back plate, both aluminum, which entire assembly will act to dissipate heat. I'll be using reed valves of some kind, and the plumbing will be pretty straightforward, with a water trap at the bottom, etc.
                              Last edited by darryl; 10-16-2010, 05:51 PM.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-