Mechanisms and design
Parts that come out already working
Seven parts, one print and no assembly step. The secret of a print-in-place mechanism also lies in the air between its parts.
Video in preparation. You can explore all the content on this page right now.
How do you print two parts together without fusing them?
Design a gap the machine can preserve. Clearance has to survive the printing process.
01 / Printing empty space
Print-in-place means making an assembly in its working position. Small clearances separate the parts. Too little clearance can fuse them; too much creates play. A clearance test helps find a combination that works for that machine, material and setup.
02 / A small planetary system
The script’s design has a 12-tooth sun, five 8-tooth planets and a 28-tooth ring: seven parts. With the ring fixed, the orbit of the planet centres turns at 12 ÷ (12 + 28) = 0.3 times the sun’s speed. Ten sun turns give three orbits. Each planet also spins on its own axis: that spin is different from its journey around the sun.
03 / Moving without falling apart
V-shaped or herringbone teeth help retain the parts vertically. Supports trapped inside a mechanism would be difficult to remove, so the geometry must support itself during printing. Here, the approximate 45° overhang guideline is measured from vertical; the actual limit depends on cooling, material and settings.
04 / Scaling changes the gap too
Scaling a design to 50% turns a 0.3 mm clearance into 0.15 mm. The printer does not gain resolution because the file got smaller. The first layer can also spread out: this is elephant’s foot. Checking its settings and compensation can help, but suitable clearance comes from testing, not a universal number.
Turn it and follow the marked planet
The ring stays fixed. The coral dot follows an orbit; each planet’s mark shows its own spin. This is a motion diagram, not a manufacturable tooth drawing.
Teaching model · Not results from filming.
Predict before printing
Materials: a pencil and paper; a printer is optional.
- Draw two parts separated by 0.3 mm and calculate the gap at 50%, 100% and 200% scale.
- If you have a clearance test, record which parts move using the same material, orientation and settings. Do not force parts with sharp tools.
- Compare prediction and observation. The episode’s STL files will be added when available; for now, explore the simulator.
Questions to keep you thinking.
Does three turns mean each planet spins three times on its own axis?
No. It means three orbits of its centre around the sun. Rotation on its own axis has a different speed and direction.
Is 0.3 mm the right clearance for every machine?
No. It is one of the script’s proposed values. The test includes 0.15, 0.2, 0.3, 0.4 and 0.5 mm. Filming results are still pending.
Does 45° guarantee that supports are unnecessary?
No. It is an initial guideline measured from vertical. Shape, cooling, material and layer thickness can change the outcome.
What did you take away?
Three questions, no grades and no rush. Every answer comes with an explanation.
Answers explained
With the ring fixed, 10 sun turns produce…
3 planet orbits. 10 × 12 ÷ (12 + 28) = 3 orbits of the planet centres.
A 0.3 mm clearance at 50% scale becomes…
0.15 mm. Uniform scaling changes gaps too: 0.3 × 0.5 = 0.15 mm.
What can happen if clearance is too small?
The parts can fuse. Deposited material can close the gap and join the parts.
Keep exploring
Content based on the Hands On Science script. Additional technical references: