Double-Acting Hydraulic Cylinder – Syringe Powered (Blockineer)

Blockineer Double-Acting Cylinder – printable demonstrator

"The game cheats. We do the math." – from the Blockineer video "Minecraft's Piston Door Would Need 5 Megawatts".
Watch the video: https://youtu.be/Ev-PaNE5RPc

In the video, a Minecraft piston pushes a block in 0.1 s with no power source. Real machines do it with a double-acting hydraulic cylinder – the same part that moves an excavator arm. This model lets you hold one in your hand: two syringes, one printed cylinder, and you can feel the difference between hydraulics (water) and pneumatics (air).

Two versions:

blockineer_cylinder.scad is fully parametric (OpenSCAD): bore, stroke, rod diameter, O-ring grooves and clearances can be changed in the Customizer.

What you need (besides the print)

Option: instead of printing the barrel, use a clear acrylic tube 36 × 3 mm (ID 30 mm), cut to 80 mm. Then you can watch the piston.

Print settings (made for a Bambu Lab A1, 0.4 mm nozzle)

Roughly 75 g PETG for the working cylinder, 40 g PLA for the cutaway.

After printing, smooth the barrel bore lightly: wet 400-grit sandpaper wrapped around a dowel, a few turns, then grease.

Assembly (working cylinder)

1. Test-fit the rod in the piston (tight fit). Glue it with epoxy, rod end flush with the piston face.

2. Put the 25 × 2.5 O-ring on the piston and grease it.

3. Fold the 8 × 2 O-ring into a kidney shape and press it into the groove inside the front cap bore. Grease.

4. Slide the rod through the front cap from the spigot side.

5. Glue the rear cap into the barrel (epoxy into the glue groove). Let it cure.

6. Push the piston into the barrel and glue the front cap. Turn both caps so the ports point up, opposite the feet.

7. Glue the barbs into the sockets (epoxy, sparingly). Clear the channel with a 2 mm drill if glue got in.

8. Press the rod end onto the rod.

9. Tube from port A (rear cap) to syringe 1, tube from port B (front cap) to syringe 2.

Using it

Hydraulic (water): fill both syringes and tubes with coloured water and push out the air bubbles (cylinder ports up, cycle a few times). Push syringe 1 → the rod extends and syringe 2 fills. Push syringe 2 → the rod retracts. It is stiff and precise – water barely compresses.

Pneumatic (air): connect with air only. Now it feels springy and lags behind your thumb – air compresses. That is why excavators use oil, and why the Minecraft piston "cheats": it moves a block instantly with no fluid, no pump and no energy.

The math (matches the video)

• Piston area: Ø 30 mm → A = 7.07 cm²

• Rod side (minus Ø 8 mm rod): 6.57 cm² → retracting is about 7 % weaker but 7 % faster. That is the typical asymmetry of every double-acting cylinder.

• Full stroke (50 mm) needs 35 ml on the rear side and 33 ml on the rod side → that is why you need 50–60 ml syringes.

• Force: F = p · A. About 2 bar from your thumb on the syringe gives 2 × 10⁵ Pa × 7.07 × 10⁻⁴ m² ≈ 140 N (≈ 14 kg) – minus O-ring friction.

• Pascal's trick: a 10 ml syringe (≈ 1.6 cm²) instead of a 60 ml one gives about 4.4 × the force for the same thumb, but you have to push 4.4 × as far.

The real excavator in the video does the same thing at ~350 bar with cylinders as thick as your arm.

Files

• blockineer_cylinder.scad – source. Export single parts with openscad -D 'part="barrel"' -o barrel.stl blockineer_cylinder.scad

• *.stl – ready to slice

• parts_preview.png, section_preview.png – images

Credits & licence

Design: Blockineer (YouTube) Licence: CC BY 4.0 – share and remix, please credit Blockineer.