Air Engine





Introduction: Air Engine

Inspire the next generation of engineers, challenge their ability and push the boundaries of what they thought a 13year old can make and challenge what you think a teacher can teach!

This is a project I run in my after school engineering club, normally air/steam engines are difficult to make and even harder to get running, I studied various plans and developed this relatively easy build..........even a poorly made example will run. It is a proud moment for both the student and the teacher when they complete and run one of these. Check the video to see one in action.

Learning Objective

Students will apply a series of fundamental engineering skills using a variety of equipment and machinery to work with precision, this includes lathes and milling machines. They have the opportunity to either work independently from a step by step guide or if unsure about a process can ask a friend or teacher for guidance enabling them to learn a new skill. Students aim to recall previously learnt skills and apply in a more challenging situation, they have to use a metal lathe to drill to a precise depth, parallel turn to a specific tolerance,  and......... they will also learn how to cast aluminium. This project is a skills challenge and a massive confidence builder.

Future learning objective

I am intending on expanding this next year to include scientific calculations.
  • F=MA
  • PSI Vs RPM graph
  • Efficiency

Step 1: Students Work

Here are two typical examples of a students work.....remember these kids are only 13!

Step 2: Fly Wheel - Making the Mould

Materials; Styrofoam 75 x 75 x 20mm + 30 x 20 x 60
  • Scribe a Ø70mm circle on the Styrofoam using a divider or compass
  • Cut out with a coping saw then use the disk sander until round
  • Collect a 'runner' and cut a V groove in the top then flatten the other end on a disk sander
  • See teacher to stick together with superglue.

Step 3: Fly Wheel - Casting

I am fortunate enough to have access to a crucible in my school workshop if you dont build your own by searching instructables for 'back yard foundry' 
  • Take a metal container and add 20mm of sand in the base
  • Add the mould and bury in sand so top of the runner is sticking out roughly 10mm
  • Get teacher to pour aluminium into mould

Step 4: Fly Wheel - Preparing the Casting

  • Cut runner off casting
  • Clamp and drill Ø6.8mm hole through the centre of the casting then tap a thread at M8
  • Take a large diameter aluminium or steel rod (Ø25mm or above). Centre drill it and then drill a Ø6.8mm x 30mm hole
  • Cut the head off a M8 x 50mm bolt, file the sawn edge and put into the rod

Step 5: Machining the Casting

  • Screw casting onto the machining arbour
  • Parallel turn down the sides until its round round
  • Face off the front of the casting

Step 6: Fly Wheel - Machining the Recess

  • Set up the cutting tool to cut the recess 3mm deep into the side, leave approximately 9mm from the outside and middle
  • Set the parting off tool to 450 and chamfer edge
  • Remove the casting from the arbour and flip it around to repeat the machining on the other side.

Step 7: Fly Wheel - Drilling the Holes

  • Using the Digital calliper accurately measure the inner and outer circles then create the 5 centre holes to lighten the flywheel using 2D Design to make a template.
  • Drill a small pilot hole Ø4mm
  • Drill a Ø8mm hole
  • Using the deburing tool tidy the holes you have drilled.

Step 8: Fly Wheel - Drilling the Centre

  • Carefully clamp the flywheel onto the pillar drill and drill the centre to Ø10mm and deburr edges

Step 9: Cylinder - Facing & Drilling

Materials; Aluminium rod Ø25mm x 55mm long
  • Face off both ends and chamfer.
  • centre drill and drill at Ø10mm to an accurate depth of 45mm.
  • Use the digital calliper to check depth and re-drill if necessary.

Step 10: Cylinder - Machining the Flat

  • Set up work in milling machine to create a flat edge approx 4mm wide
  • Level the work piece using a fixed scribe
  • Use a digital calliper to check the width of each end. if its parallel your work is level
  • Now keep milling until the flat is 15mm wide.
  • The image above shows what happens if its not get a tapering cut on the surface

Step 11: Cylinder - Drilling Holes in Flat

  • Measure and mark the holes as per the working drawing, holding your work in a V-Block, centre punch, centre drill and drill the holes into the flat.
  • Put the cylinder back into the lathe and re-drill at Ø10mm but be carefull not to make the hole any deeper (this removes any burrs from drilling the small holes into the flat..
  • Use a countersink to deburr the edges of the hole.
  • Sand the cylinder to create a good surface finish.

Step 12: Cylinder - Axel

  • Cut a Ø6mm steel rod to 30mm long
  • File a chamfer on each end
  • use a M6 die to cut an external thread 20mm long
  • Thread lock into the 6mm hole in the cylinder

Step 13: Piston

  • Cut Ø8mm rod to 40mm long
  • Face and chamfer both ends of the 8mm aluminium rod.
  • Mark out and centre punch, then Drill Ø3.2mm hole as per the video and drawing below.
  • Machine some Ø12mm nylon rod as per the diagram above
  • The nylon is hammered onto the aluminium

Step 14: Chassis - Marking Out

Print the working drawing ensuring the CAD software you use does not alter the scale. you can use the printout as a template.
  • Cut out a template
  • Use tape to stick template onto steel plate, ensure the bottom of the template is aligned with the bottom of the plate
  • Scribe around chosen template with a ruler and scriber
  • Ensure the paper is pressed flat against the steel then centre punch the crosses.

Step 15: Chassis - Drilling Holes

  • Clamp the steel into a drill vice ensuring it is gripped on the top shelf
  • Use a medium centre drill to drill and the holes approx 2mm deep
  • Use the appropriate drill bit for each hole according the working drawing
  • Remove steel from vice and use the deburing tool to tidy up the edges

Step 16: Chassis - Cutting

  • set up the chassis in the milling machine
  • Mill the two longest sides down to the scribed lines
  • Cut the top edge off with soft jaws and a hack saw

Step 17: Crank Ring

• Carefully measure distance between piston and chassis
• Face off Ø25mm aluminium rod, centre drill, drill Ø10mm x 10mm deep
• Chamfer the outer edge
• Part off at the correct thickness
• De-burr holes.
• Center punch  4mm in from edge, drill Ø3mm.
• Cut Ø3mm steel to 12mm long and FILE a chamfer on the edges and thread lock it into the crank ring

Step 18: Support Rods

  • Use Ø12mm aluminium rod and create two pilers as per the working drawing
  • Drill the side hole on a pillar drill
  • Thread all four holes with a M5 tap

Step 19: Base

  • This is precut for the students as they are not allowed to use a router
  • Students can mark and drill the holes
  • The measurements are taken from the hole centres on the chassis
  • The diameter of the holes is Ø6mm for the clearance and Ø10mm fro the counter bore

Step 20: Assembly

  • The flywheel and crank are attached using a Ø10mm steel rod that is long enough to go through the fly wheel, chassis, and crank ring
  • The axel should be stuck using not get threadlock in the chassis or the wheel will not turn
  • They cylinder is held with a spring and a M6 nut
  • The support pillars are fixed using a M5 bolt cut to size
  • The base is fixed to the engine with 30mm long M5 bolts

Step 21: Enjoy

This example has a very heavy flywheel so is much slower than the one shown on the fist step.

If you have any questions about this please ask.




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Do you sell completed versions?


Beautifully made! You are a craftsman.

will it work if its made in a larger size

Hi there. I've been looking for a tutorial on how to build a minni diesel engine for my year 10 science project but haven't found anything that can help me, luckily Google helped me find this tutorial. It's not diesel but I'll enjoy making it either way. Thanks so much from Wynberg Girls High school, South Africa!

Nice air engine! did you try it with steam?

These is my steam engine from student project:

now make it street legal... and go 60mph

you should make the kids do everything. My grandfather tought me the lathe and vertical milling machine at age six (am 14 now)

Can you tell me how the air supply is fitted, is it just a push fit?
Also what length, diameter and strength spring is best to use?


hi, good questions :) air supply is just push into the hole. a light spring is best, the nut allows adjustment of pressure.

could you please tell me the dimension thickness of the chassis this would be much apreciated