Compressed Air Engine

Files for the compressed air engine used in the following project: FDM printed parts: Crank Case (Front, Rear) Crank Shaft Bottle Lid Engine Mount Piston Head Cap Resin printed parts: Cylinder Head Conrod Piston Seal Mold Other Required Parts: Bearings OD 16mm ID 8mm W 4mm (x2) O-ring OD 7mm ID 3mm CS 2mm (x1) O-ring OD 10mm ID 4mm CS 3mm (x1) ** O-ring OD 22mm ID 18mm CS 2mm (x1)** No. 2 ¼" screws (x3) 6mm plastic ball (x1) Tube OD 4mm ID 2mm ** Pneumatic fitting 1/8" (x1)* M3 x 10mm (fitting prop adaptor to shaft) (x1) M2 Set Screw (adjustable piston pin) (x1) 1.5mm wire (Crank shaft pin, where conrod pivots) Acrylic tube OD 15mm ID 13mm CA Glue or Epoxy to attach parts *only for standard engine **only for bottle mount engine Cylinder To get the correct cylinder length and exhaust port positions, I build the bottom end of the engine (crank case, shaft, conrod, piston). Then push fit (don't glue yet) the cylinder into the crank case, turn the crank until the piston reached the top, then mark 4mm above the piston and cut the cylinder to that length. That should mean the cylinder head is about 1mm above the piston when glued in position due to it's 3mm glued section. Then move the piston down to the bottom, and mark where to drill the exhaust ports. I use a 1.5mm drill and evenly space 4 holes. Then glue the crank case (rear or bottle lid mount), cylinder and cylinder head together. The bottle mount version also requires the air tube to be glued in at the same time. Piston Seal The 'Piston Seal Mold' is a mold for a mold. I printed it using resin, then poured in R PRO 20 Silicone to create a flexible mold. Then used Polycraft DuroFlex 40 Polyurethane Liquid Casting Rubber to make the actual seal. I show the molding process at 11:24 in this video: It's a bit of a long and delicate process, so I've included a model of the seal itself if you're able to print it directly in resin (Would need shore hardness 40). This latest piston seal doesn't require glueing to the piston, it should be a friction fit, so replacing pistons doesn't require new seals.