I've designed a rebreakable karate board to test your strength.
I've made 3 difficulties, an easy, medium and a hard board, from 10mm to 15mm thickness, the 10mm one is very easy and is mainly designed for children, the 12mm and the 15mm ones are quite more difficult and require a lot more effort than the easy board, please note that the strength needed to break these boards are not the same as proper karate boards on the market.
The test prints sounds like what its supposed to do, to test if it fits/works or not, these are printed with quite a bit of tolerance, the same as the boards itself ,so if your prints don't function as intended, then there is something wrong with your printer, you can also use the test prints as fidget toys and can be very satisfying to snap.
Please print the boards the intended orientation since this is the strongest orientation and also so that the boards fit together properly, and also enable brim since you would need a lot of layer adhesion for the board to print out well, even with a good print bed.
Please note that the 12mm board hasn't been tested yet and may have some clearance/durability issues putting it together, and also some boards may require some persuasion for them to slide on, but after a few uses should be a lot easier to put on, and please also note that these boards aren't perfectly designed and may have some other issues since this uses up so much filament just to test out
I also take no responsibility in any harm that is caused by this product and should be used with care.
If you would like to support me and help me buy more filament so I can test and make more designs, you can send money via paypal through this link: https://www.paypal.me/GeorgeElliott11