I wanted to make a DIY Knife Handle for one of my Japanese beginner knives, and figured that I might as well take advantage of my CNC router as I already have it. The first handle I built was inspired by the octagonal Wa-Handles, specifically with the dimensions listed on coltonhandcrafted.com. I used these dimensions to model the handle in Fusion360, and then split it into several parts to experiment with different wood looks:

Note that instead of building the handle from a single piece of stock, it is instead layered, with the middle layer being sized to fit the tang. This allowed me to use my Workbee CNC router to cut all pieces, assemble them, and then grind them to a smooth fit.

I ended up pouring the ferrule/top bit out of epoxy mixed with black acrylic paint since I didn't have any black wood around. I first attempted using a silicone mold created from a 3D printed ferrule, but these ended up too bubbly, so instead I poured smaller epoxy squares and just ground them into the right shape:

After sanding the handle down to a smooth finish, I stained it with a mix of Beeswax+Mineral oil, and pressure-fitted the knife: