>>411611...continued.
Some tips,
Align the wood grain opposite from what you see on mine in that image in
>>411321 The vibrations flow better through the wood when the grain is radiating away from the bridge. It also helps strengthen the bridge and prevents the bolts and tee nuts from lifting/bending the top board off the sides.
Put the sound hole in the center, so both thumbs can reach it. You can place either thumb over the hole to change the sound as you play. It should also be about twice the thickness of your thumb. Too large and it won't work well to change the sound with your thumb and too small and it won't work as well projecting the sound. Being perfectly circular or oval produces the best sound, but you can always experiment with styles.
Make the box/board only as wide as you can comfortable reach your thumbs just passed the center tines or sound hold in the box.
You can install piezo pickups inside the box to allow the unit to be electric or acoustic. I recommend installing 3 of them. One on the bottom of the inside of the box and 2 right under the sound bridge.
You can make the sound box rather large so it sticks out way passed the sound bridge and experiment with various styles and sounds.
Some kalimba have two holes on the bottom or sides that you cover/uncover to change the sound.
Any box, metal or wood, can be used to make a kalimba. The bridge is the most important part to get right. You can even just use a board and no soundbox. A flat bottom is best for setting it down. Hardwoods are best for the sound. Boxes should be designed with the thinnest wood without compromising durability.
>pic of a few instruments I made, the acorn-shaped kalimba was purchased. It is made from a gourd, but is terrible to get to sit on a table as it wants to flip over constantly. 