Same thing you do for cutting 13cm into thirds: make one third a bit fat. Go 4 1/4, 4 1/4 and 4 1/2". Or construct it.
That’s not a problem I face in the wood shop a lot though. A more practical problem: We tend to mill boards to 3/4" in thickness. To do a half-lap joint, you need to cut away half the thickness of each board and then lap them over each other, you can set your depth to 3/8" and you’re there. If I’m going to do a bridle joint or a mortise and tenon, a third of 3/4" is 1/4". Show me a third of 19mm on a metric ruler. I’ll show you where it is: 6, 6, and 7mm.
Same thing you do for cutting 13cm into thirds: make one third a bit fat. Go 4 1/4, 4 1/4 and 4 1/2". Or construct it.
That’s not a problem I face in the wood shop a lot though. A more practical problem: We tend to mill boards to 3/4" in thickness. To do a half-lap joint, you need to cut away half the thickness of each board and then lap them over each other, you can set your depth to 3/8" and you’re there. If I’m going to do a bridle joint or a mortise and tenon, a third of 3/4" is 1/4". Show me a third of 19mm on a metric ruler. I’ll show you where it is: 6, 6, and 7mm.