Working steam engine model using compressed air.

Tolerances are tight between the pistons and the engine housing, but will lossen up with a bit of use. This may require a gasket between the top and bottom engine blocks depending upon the flatness/tolerances of your top and bottom layers. M5 bolts, nuts and washers are required for all connections and lock nuts are suggested for the linkage arms.

For Teachers and Students:
This is an excellent teaching aid for showing the components and mechanisms of action for a steam engine and for converting linear motion into rotary motion. This is a basic model of the James Watt engine. Students and teachers can learn more about this at:

https://study.com/academy/lesson/james-watts-steam-engine-facts-lesson-for-kids.html
https://www.bbc.com/teach/class-clips-video/the-invention-of-the-steam-engine/zkvygwx
https://medium.com/@badeekhoury/the-father-of-all-engines-the-steam-engine-9f53053e870

Assembly Notes:
Recommend a strong filament such as ABS or Nylon for a working model, but PLA will also work. Use the minimum air pressure possible to create movement - less than 10PSI should be more than adequate. It is better to have to hand start the movement than to use too much air pressure.

Note that the shafts of the Drive Piston and the Valve Piston are intentionally a bit larger than the corresponding inlet holes in the engine body, and are shaped as polygons instead of tubes. This is to allow for sanding of the shafts to match the profile of the engine inlets given different printer tolerances. A tight, but still moveable, fit is necessary to avoid undesired pressure loss, so some manual tuning is required. Some dry lubricant is also recommended on the shafts as well as the internal moving components.

The engine body may need to be elevated on a small platform to create a horizontal alignment of the drive shafts with the crank assembly. In theory, the double-jointed shaft assemblies should allow for the variance in height (as is the case in actual steel / iron engine components) but plastics may not provide the rigidity that metal provides. Raising the engine block may minimize undesired torque on the shaft assemblies and improve performance.

Additional assembly notes regarding the valve shaft are included in the pictures.