Thursday , February 22 2018
Home > Engines > New Project: Plans for a Simple Air Engine

New Project: Plans for a Simple Air Engine

Material: Aluminum, Steel, and Brass
Units: (in)


If you’re looking for a simple engine to build that runs on compressed air, here’s a nice set of plans for you. Here’s what Rob had to say about his plans:

“This was the semester long project we did in class for Machine Tool Technology at the University of Central Missouri . I would like to hook the engine up to something and do tests.

The base is made out of a 3/4 in thick aluminum and the body and cylinder is mild steel. The flywheel and crank is made out of brass. I used most tools that you would use with metals. Vertical mill, horizontal mill, metal lathe, drill press and grinding machine, thread tap. I even machined the threads on the wrist pin.”

– Rob K.

Here’s a video of the little engine in action:

Thanks for sharing your plans Rob!

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About Tyler

Tyler is a hobby machinist and 3D printing aficionado. He teaches computer programming and web development at Highline College near Seattle. Tyler founded Projects In Metal in 2008 because he was frustrated by the lack of free plans available for hobby machinists.

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  1. Tyler


    I am planning on building this air engine just for fun.  Do you know whether or not there is an exploded view of all the parts in real life, not a drawing?  The part I am unsure of is the shaft and wrist pin.




    Mtw fdu.



  2. Sorry for the late reply.

    I don't remember seeing an exploded view anywhere, but you can contact the original author via his instructables page. Here's the link:…

    If you find an exploded view somewhere, be sure to link to it for the reference needs of others. 

  3. Will do!!!!


    Cheers Tyler!


    Here's what I have done so far.


    Image Enlarger


    I have made 2 changes to the material for the base is mild steel and the gear is made from nylon.   The square block on the end is still to be machined down to 3/4 x 3/4.  That and the wrist pin(which I ended up working out) are the only 2 bits needed to finish  this off.  This has been a fun project to make.


    Mtw fdu.



  4. Looks good so far!

    We are going to need a video of the little engine running … Smile

  5. Shall do!!!


    I am going to be busy at work for the next 5 days  so maybe any time after that I can organise a video for you guys to check out.


    Mtw fdu.



  6. Here is a pic of my Simple air engine:


    Image Enlarger


    Here is the link to the video.  At the moment it is not operating with the air  because my air supply is not enough.  I am going to get a air fitting to  permanantly have it setup.   There is no voice overs just me turning it by hand with a few different views.  The video goes for 2:24.  My apologies for some of it being a bit blury.




    Mtw fdu.






  7. Looks good!

    Why plastic for the flywheel? No bar stock large enough? I doubt it will matter with this engine, but with other engines having a heavy flywheel will help the engine run better.

  8. I have got the right size brass stock there but I have ear-marked  it for another job which I am currently doing for a customer.  I have got very little of it in stock so Nylon was the next thing to use (I have got an ample amount of this).


    Mtw fdu.



  9. Are you sure it's not running because of air supply? I'm not familiar with the engine in detail, but I can imagine that the fly wheel simply isn't adding enough intertia to get the piston back to past top dead centre. I'd sort that to be honest Mtw as I guess it'll stutter after less than one rev as it is.

  10. If you look at the video, in the background, there is a air blower gun which I just put up to the inlet side of the engine.  I was not able to hold this on the hole correctly and at the same time spin the gear around.  I need to connect the air up like the 1 in the first post of this thread.  I have read somewhere it has a rating of 1000rpm at 40psi.  There was no way I was delivering that much air with my blower gun.


    This should explain it a bit clearer.


    Mtw fdu.



  11. If there's enough weight in the crank web and counterbalance you stand a chance, but I'll stick with my thoughts as the engine is utterly dependant on the flywheel action for most of its rotation. At the very least it'll need speed to overcome this with your lighter flywheel, so it may work at the higher rev ranges.


    I'd love you to prove me wrong though to be honest so that it works for you, as I said I'm not close to that particular engine, so I'll wait to see what prevails.

  12. I will re-post the out-come as soon as time permits me to do so.


    Mtw fdu.



  13. Smaller engines will run fine without much of a flywheel.  However, they will not run at slower speeds, and will require more air pressure.  Since I prefer my engines to just tick over, as opposed to running flat out, I tend towards a slightly oversize flywheel, and usually use brass.  More mass will allow the engine to coast more, and let you run the engines on very low pressures – less than 2 PSI  in most cases.


    With such a small engine, even adding a rim of steel (think galvanized conduit) will help with lower speed performance.  Black iron pipe would also work well. 


    BTW, if there are children in the neighborhood, invite them to look at your engines.  Kids love to watch them run.  I get asked at least a couple of times per year to bring out the ones I have made and run them.

  14. How do you put this engine together?

  15. Looks a lot like a simply air engine from a machining book, we have in metal shop. I might scan them and then start a new thread.

  16. I haven’t built this engine myself, I shared it with permission from the original builder. What part of the assembly are you having trouble with? Have you machined the parts yet? I think as you machine each part you’ll start to get an idea of how everything goes together. But if you’re stuck let me know and I’ll try to help with the assembly.

  17. Ok. Yea thanks. But as you said I think I’ll be able to see it better when I have everything done in metal shop. But If I have questions I will for sure ask.

  18. Sounds good. Happy turning!