Print-in-Place Planetary Gear Spool Cap ⚙️

Not just another spool cap with a picture on top. This one actually moves!

Instead of using the top surface only for a logo, picture or decoration, I wanted to make the spool cap itself functional.

The result is a compact print-in-place planetary gear mechanism integrated directly into the spool cap.

Turn the outer ring and the gears inside start moving. The complete mechanism is printed already assembled — no screws, separate pins, glue or assembly required.

Just print it, carefully free the moving parts and enjoy the mechanism. ⚙️

Fully functional & print tested

This is not just a CAD concept.

The complete mechanism has been physically printed and function-tested on an FDM printer. Gear engagement, clearances and movement have all been verified on a real print.

The design uses:

45T internal ring gear

3 × 12T planetary gears

21T center gear

Print-in-place construction

Integrated spool cap

No assembly required

The entire mechanism was designed to stay as compact as possible, while still being printable and functional.

⚠️ Important – freeing the mechanism after printing

Please take your time when moving the mechanism for the first time.

Because this is a compact print-in-place mechanism with small clearances around the gears, some areas may be slightly connected or tight immediately after printing. The exact result will also depend on your printer calibration, material, extrusion and first-layer settings.

Do not force the outer ring aggressively.

Carefully work the moving parts back and forth and gradually free the gears. Once all print-in-place clearances have been released, the planetary mechanism should move normally.

The mechanism has been successfully printed and tested, but good printer calibration is important for the best result.

Two 3MF versions included

I have prepared two different 3MF files:

🎨 Multicolor 3MF

Prepared for a true multicolor print. Different parts of the planetary mechanism can be printed in different colors, making the movement and interaction between the gears much easier to see.

This is also the version that really shows that this isn't just decoration — the entire top of the spool cap is a working mechanism.

🌈 Standard / Layer Color Change 3MF

Prepared for a normal single-extruder printer.

You can create a multicolor effect by changing filament at selected layers. Filament-change layers need to be set in your slicer according to your chosen layer height, printer and desired color combination.

So you don't need a multicolor printer to make the mechanism stand out.

Why a planetary gear?

Because a spool cap doesn't have to be just a cap. 😄

I wanted to use the available space for something mechanical, functional and satisfying to play with. Instead of simply putting another image on top, the planetary gear itself becomes the design.

It can also be used as a simple demonstration of how a planetary gear system works — especially with the multicolor version, where the movement of the individual gears is clearly visible.

Number series

The current version includes number 1.

If there is interest, I can also prepare a complete 2–8 series, using the same functional planetary mechanism.

Print it. Free it carefully. Turn the ring. Watch the gears come alive. ⚙️