Stool

I had a plank of beech left over from making the bed, and I wanted to try box joints, and we needed a gardening stool (2 out of 3 of these statements are true :-))
Problem one was that the router bit I bought wasn’t 10mm, but varied between 9 and 9.5mm – needless to say the joints didn’t fit. Woolcraft send me a new bit. When testing on some scrap pine all was OK, but on the beech the router bit kept slipping down during the cut, no matter how hard I tightened it up (any ideas?). Also I was never sure whether it was cutting through the wood or burning my way through it, but I’ve read this is a “feature” of beech.
I’d hoped the end-grain on the joints (my wife calls them “the stiches”) would show up more. It’s also kinda heavy.
Learned a lot, could do better, will do better, 6/10.