Balance Board Roller

I'm not sure if “roller” is the right term, but this is a round bottom piece to make a teeter board or balance board, for physical therapy to treat balance issues or just to balance on for fun. Note: this is absolutely not in any way a certified piece of medical equipment, it's just something I made, so use the design at your own risk. 

The piece of ¾" scrap plywood I used is about 30" x 12" and has 3 of these parts attached side by side. They have built-in alignment pins on the edges to help position them. The screw holes are designed for 1" drywall screws so they won't go completely through a ¾" thick board. I used a piece of tape on the drill bit as a depth gauge so pre-drilling the holes wouldn't go all the way through the wood. 

I made this for my daughter, who weighs about 120 lbs, and I have no idea what the max load is, but I weigh 170 lbs and the finished board as shown holds me. I did not use any engineering to calculate how thick the parts should be, just took a guess, and set the infill at 30% which seemed reasonable. Print time at 80mm/s on my Ender 3 was 10 hrs per part. Printed in PLA.