Adjustable angle wobble board (ankle / balance exercise board). For improving balance, strength, etc. Do not use for rehabilitation without consulting an appropriate medical professional.
The board adjusts by having a main curved wobble base, wobbleA.stl, together with two optional inserts, wobbleB.stl and wobbleC.stl. With the default dimensions, if you put in just the wobble base, you get 12 degrees of motion away from vertical. If you add insert B between the board and the wobble base, you get 15 degrees, and with all three pieces, you get 17 degrees.
The wobble base uses a captive hex nut. You need to pause your print at the right point (use slicer preview to see where the nut ends), insert the nut, and continue printing. I recommend preheating the nut by putting it on your print bed and putting some glue stick on it to improve plastic adherence.
I used a router to cut a round wooden board out of 3/4" Baltic birch, because I had some from an abandoned project. You can also use a jigsaw, but it probably won't be as neat. I recommend printing in PLA with 50% infill, with extra solid layers inserted (e.g., every 20 layers) and with four shells.
* 450mm diameter wooden board
* radius of curvature for wobble base: 105mm
* 5/16" carriage bolt cut to 39.5mm (longer will damage plastic), not including head
* hex nut inserted before print reaches 16.75mm thickness
* insert B thickness: 11.1mm (make out of wood to save plastic)
* insert C thickness: 7.4mm (make out of wood to save plastic)
If you change the wooden board diameter, the angles printed on the undersides of the parts won't be right. If you want the ability to change the diameter, you may want to customize by turning off angle labels.
All these are adjustable in the Customizer. Choosing the angle number chooses whether to make the base (angle 0), or insert B (1) or C (2).