I needed to cut am 20cm wide and 18mm high board and the side had to be in a 90° angle with a nice straight cut.
So i designed this guide for my japanese Kataba saw.
To get the guide completed you will need 4 threaded rods with nuts. I used M5 *330mm rods and it worked great.
Until now I have used this guide for 8 boards and it seems to work great with my Kataba.

The slot is only 1mm wide so it is perfect for japanese saws. If you want to use other saws you will probably have to widen the slot.

printed with 2 layers of 0,2mm ABS filament and 15% infill. I am sure other combinations will work good.
Make sure the guide is laying flat for printing so the grain can handle the force from the rods better.