This is a simple actuator/automata display model of the Scooby Doo mask reveal meme. I like the meme template and wanted to turn it into a fun 3D printable model to have on my desk, especially at spooky halloween time. The print features a rack and pinion gear machanism which translates linear motion into circular motion. By pushing the rack, Fred's arm will reveal the villain by unmasking him in a smooth swoop.

The assembly requires NO glue and NO externaly sourced parts, everything is 3D printed. The model is modular so you can design your own frontplate which utilizes the same mechanism and just exchange it (a blank FRONTPLATE is availlable in the files). All parts can be printed in approx. 3 - 3.5 h with BBL P1S with a 0.4 mm nozzle.

The mechanism parts (BASE, GEAR and RACK) are designed for easy printing without suppports and print collectively in approx 1.5 h (P1S). The model somewhat relies on tight tolerances in order to be assembled. The most "important" tolerance is between the gear and the moving arm so they can be friction fit together but still can be disassembled later. Since the tolerances vary strongly between printers, printer models, settings and filament, I have provided multiple gear models with different tolerances on Plate 02 to be printed separately, from which you can choose which one fits best (15 min for 4 gears on P1S with 0.4 mm nozzle). The gears are quite small and do not consume much filament, and in my builds GEAR_3 worked best.

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The FRONTPLATE features 8 colours printed in one layer which required a little bit of slicer trickery for printing with only one or no AMS.

PLEASE READ THE PRINT INSTRUCTIONS CAREFULLY ON HOW TO PRINT THE FRONTPLATE DEPENDING ON YOUR PRINTER SETUP!

• If you have two AMS units (you lucky person) then the print is simple and straight forward (see 2xAMS print profile and the corresponding print instruction).
• If you have “only” one AMS, then you are limited to 4 colours/layer and you would need to print the FRONTPLATE from two plates. Please refer to the print instructions for printing with one AMS (1xAMS) and read it carefully before printing!

I added a small piece of the frontplate to test if the method works for you (1xAMS_TEST). If you are uncertain please try to print this first :)

I am also working on using the same method without needing an AMS at all but unfortunately it is not 100% straigt forward as in this presented solution. As soon as I have it ready I will post it here :)

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The assembly is mostly intuitive but I have included a comprehensive assembly instruction as a PDF as well as a short video below :)

I am looking forward to your makes and your feedback!

Happy printing and HAPPY HALLOWEEN!

Printed and tested on BBL P1S with one AMS. 0.4 mm stainless steel nozzle, Textured PEI build plate.

Print settings:

BASE: 0.2 mm layer height, 3 walls, 10% hexagonal infill, 0.8 mm bottom layers, no top layers, arachne

STANDS: 0.2 mm layer height, 3 walls, 10% gyroid infill, 3 bottom layers, 3 top layers, arachne

GEAR and RACK: 0.2 mm layer height, 4 walls, 100% infill, 3 bottom layers, 3 top layers, arachne, (top surface ironing for RACK)

ARM and all colours for the FRONTPLATE: 0.2 mm layer height, 3 walls, 100% infill, 3 bottom layers, 3 top layers, arachne

Used filaments for the print in the pictures:
BACKGROUND: eSUN PLA+ navy blue
COLLAR and JEANS: GEEETECH PLA blue
SCARF: BambuLab PLA Basic Orange
HAIR: eSUN PLA+ yellow
SKIN: eSUN PLA+ bone white
OUTLINE: eSUN PLA+ black
ROPE: eSUN PLA+ dark brown
CLOTH and FRONTPLATE: eSUN PLA+ white
BASE, GEAR, RACK, STANDS: eSUN PLA+ black

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Here is a quick Q&A with potential questions:

Q: Why is the printing of the FRONTPLATE with one AMS or no AMS so complicated?

A: If you want to print more than 4 colours with only one AMS (or no AMS at all) you usually can introduce a GCODE command for pausing the print and changing the filament. However, as far as know in Bambu Studio this command can only be easily implemented between layers and not inside a single layer. The model was designed to print all 8 colours on the first layer only (@ 0.2 mm) to minimize filament consumption (since you don’t need the same colour stacking on top of itself) as well as unnecessary filament switching. Therefore, you need to do such a trick to allow more colours to be printed inside one layer.

Q: My TEST print looks bad. The colours from the second plate have gaps and do not look smooth.

A: This has to do with the nozzle height. I had the same issue even after taking care of the previous point, so I ran the built-in calibration of the machine again and after that it worked on the first try. Another issue could be that despite deactivating bed leveling, the start GCODE still features a quick probe at the center of the bed before printing. If some of your previous prints were at exactly this probing spot, then the Z-offset will be wrong which leads to the nozzle being too far away from the bed resulting in “ugly” surfaces. Make sure that your nozzle gets wiped clean before starting the second plate print. Also make sure that your build plate/bed is clean and has good adhesion.

Q: Why does the BASE have no top surface?

A: This was more a strategic decision to minimize print time and filament consumption. Since the FRONTPLATE covers the top of the BASE anyway you will not see the infill and vice versa you would not see your pretty top layers. The infill was chosen to be the most rigid by consuming the least amount of filament (and hexagons are still bestagons).

Q: Why is the rest of the FRONTPLATE white?

A: This decision was made to make the white parts of the design (e.g. shirts) as white as possible. Each filament has a certain transmission distance (TD) which tells you how “see-through” a certain filament colour is. Standard white PLA usually has a quite high TD meaning its very see-through. If you print only one white layer and a darker layer on top of it (= behind it if looking at the final model) the dark layer will be visible through the white layer and the white will look very darkened/dull. Therefore, the rest of the FRONTPLATE was printed in white to minimize such effect.

Q: None of the gears fit well to the arm. The hole is either too large or too small.

A: Try to re-scale the GEAR model in the slicer (in a range of ± 0.5% at max, otherwise the GEAR will not fit into its hole in the BASE if scaled up too much). Reprint and see if it fits. If the GEAR is too loose, you can try jamming a small piece of filament, e.g. a piece of the priming line, between the GEAR and the ARM pin from the exposed back side. However, if nothing helps, you can glue the GEAR to the ARM after assembly, but then you will not be able to disassemble the model anymore :(

Q: The position of the ARM is too high/low from in the resting position when assembled.

A: Make sure you inserted the gear in the right way as described in the instruction. Otherwise, the tolerances of the rack could be the problem. You can try to up-/downscale the RACK model in the slicer by a bit (also around ± 0.5% at max) and see if this works. If the ARM is too high you can file down a bit off from the right stopper of the RACK (where the gear teeth are attached, see picture) which will shift the minimum position of the ARM, however this could be a bit tricky.

Q: Why do I have some strings of different colour on the FRONTPLATE?

A: This is due to stringing and unfortunately not that easy to “fix”. You could try to change the retraction setting (e.g. increase retraction speed) for the filaments you are using (under Filament Settings → Settings Override) but I have no experience with changing those values.