Eyebrow Puppet Mechanism (3D Print + Laser Cut)

For this project I made a mech for a puppet that will go on top of the upper mouth plate of a puppet so that its eyebrows can "wiggle" up and down and emote with them. This design is meant for a slightly scaled up and modified version of this pattern made by the late great Puppet Nerd, Adam Kreutinger. This design is based on this video demo of a mech designed by BJ Guyer, which I've been adapted to be made mostly in Fusion for a combination of 3D printing and Laser Cutting. I was inspired to make this mech and the puppet I intended it for two years ago using these techniques and machines that were accessible to me, but the complexity of the form and my lack of experience with CAD software caused me to abandon the project. While this post does not feature the whole puppet I hope to in the near future complete this project and update this post, and possibly edit this component of the project because as you'll soon see my iteration of this mech while functional definitely has room for improvement; I will make things I'd rework or change in a future version as they come up.

BJ Guyer's Original Mech (Stan Winston School)

-Fusion360 + Adobe Illustrator

-Epilog Fusion Maker 36 Laser Cutter

-Original Prusa MKS4 3D Printer (any 3D printer will work)

-1/4in thick plywood

-Two Rubber bands OR two Pull/Extension Springs

-One 1/8in(or smaller) screw eye (1-1/2in or shorter)

-Embroidery Thread/elastic/twine (if you need a substitute I recommend something with texture/grip)

-0.02in diameter straw

-Key ring

From the moment I knew that this project gave us the most creative liberties out of all of our assignments I knew I had to attempt tackling this project again. I felt mostly confident that with my new CAD + CAM skills I'd be able to recreate it and began sketching what I could observe from the video. From what I could see as well as Guyer's explanation, the mechanism works because of the spread out tension between both ends of the metal rods, one side of the tension provided by tautly tied strings on the outer sides and a spring which causes it to default to a horizontal position, when the outer strings are pulled on through the tubes on the bottom of the mouth plate with a key ring for your finger, the spring is extended the rod which runs through holes and more tubes in the eyebrow plates rotates which when the eyebrow is attached causes it to appear to wiggle up and down.

Adapting for CAD Software

I had the interesting challenge of trying to determine which of the components of Guyer's design I could realistically recreate in Fusion. I determined that I could make the wooden brow and mouth plates (laser cut), the string tubes, and the eyebrow rods (3D printed). I also thought that as an addition instead of the eyebrows being attached with dura collars, that I'd 3D print an interchangeable press-fit eyebrow piece to swap out for different expressions and styles.

Below are the Parameters I used for the form to facilitate scaling

The eyebrow and mouth plates were fairly simple laser cut press-fit pieces made with 1/4in thick plywood. For larger puppets I'd recommend 1/2 or larger which can be achieved by wood glueing multiple layers of whatever plywood thickness you have available. This version's mouth plate is a half circle with tenon holes (0.5x0.25in with 0.25 being parameterized as ply), a 1/10in hole for the 1/8in eye screw that I'll attach the springs to, and two 1/5in holes for the tubes that the string will run through. Both components are extruded to 1/2in. In a future iteration and for anyone wanting to recreate this mech, I'd make the string tubes, and eyebrow plates farther apart from each other to make the other parts easier to construct.

Laser Cut Preparation

While exporting as a DXF file for laser cutting, I ensured that within my setup under the cutting tool that my selected machine had the kerf settings set to 0.25mm, this setting was recommended to me by my course instructor and is what worked for a snug fit that reduced the likelihood to needing to hammer pieces together. I then opened my DXF file in Adobe Illustrator and sent it to the laser cutter, ensuring I focused the laser to the thickness of the plywood and that my lines were at 0.001pt.

Laser Cutting + Partial Construction

The laser cut process was fairly straight forward and I was able to use the preset for 1/4in thick plywood on the laser cutter. After putting these two pieces together with some like hammering, to make sure the fit for the eye screw hole was right and tested the diameter of the string tube holes with some straw pieces. Happy with the stability of the brow plates I moved on to the 3D printed components.

Rod

For the rod portion my instructor let me know that the structure that rotates didn't need to be a cylindrical twisted object (in fact because it would be 3D printed it's strongly recommended to reinforce the "rod") which allowed me to design a more practical part that fit well in the holes in the eyebrow plates. I designed this part with a midplane plane between the edges making up the hole on the brow plate, on that plane I sketched a circle slightly smaller than the hole to stabilze the rotation and extruded it -1.25in (while this design will work with the puppet patter I'll be using but definitely consider the thickness of the material you make the head out of). On the face of the rod potion I designed an elipses the part the springs and strings will be ran through which has a slit cut into it to slide in the rubberbands/springs.

Interchangeable Eyebrows

On the outward facing face of the rod piece I created another offset plane and sketched a circle that was 0.2mm larger than the circle it sits on using the offset tool, I then used the same tool again to create the outer edge of the press fit. I extruded that piece in two directions side one (facing forward) was 0.05in and side two (facing back) was 0.1/ I then created another offset plane on the outer face of the press fit piece (pictured below), sketched a rectangle and rounded the edges using the filet tool. The size of this part like the rod is dependent on the size of the puppet and your personal preference, so it does not affect its functionality.

String Tubes

For this piece I pretty much redid the previous step only using the two holes in the mouth plate by creating a midplane between the two edges that made up the hole. Because I didn't need it to rotate I was able to make the clearance just big enough to fit snuggly in the holes.

3D Printing

After a few attempts and adjustments I was able to print these components and processed them before moving onto constructing the mech.

With all my pieces tested I was able to put the mech together. Before threading the rubber bands through the eye screw I slid it into the brow rod hole and attaching the removable press fit brows to the front of the rods to secure it in place. Later I was able to use the straws from the prototype to further secure the rods in place. I then used a simple mid string slip knot to tie the key ring, ran the strings through either string tubes, as well as the brow rods; after tying it there I also ran the now secured string through the same tubes in the opposite direction. After ensuring that the string was taut the mech is now complete. Below are pictures detailing the construction in case this explanation is unclear as well as pictures of the various positions the brows can be in.

Final Thoughts

I am ultimately very happy with the result, there is definitely ways I'd like to improve this design, most of which I've mentioned in the above steps. As I move forward with the construction of the puppet I imagine I'll have to change the various pieces but I'll be sure to upload an updated version once it's done. I'm very grateful for all the help and inspiration I got from my instructors Devon and Emilie who's course is the reason I felt confident enough to make this mech, y'all are the best!