Four fours clock

thingiverse

I was inspired by this physicist's clock but some numbers seemed arbitrary and lacked an overarching theme. I remembered the "four fours" math puzzle: write all numbers from 0 to 10 with exactly four fours, using the four arithmetic operations; or from 0 to 20 allowing for square root. The math expressions were typeset in LaTeX. The size is 25 x 25 cm with a hole for the standard clock kit shaft. If you cut on a bigger size, remember to keep fixed the size of the shaft hole. I cut the face from 3mm plywood on a CNC router to avoid charred edges and engraved on the laser cutter. I tested several clock kits and settled on this reliable one. If you use different kits or materials, you may need to adjust the supplies; e.g., if the material of the clock face is too heavy for the shaft on the clock kit, you may need to add a D-ring at the back of the clock face. The clock face could also serve to spark children's interest in math. If you use it for that purpose, please report your results here.