Start with a 9" x 2" universal edger blade, $5 at Home Depot. Scribe a line at some angle. I chose 30°, or 60°, depending on how you look at it.
Cut along the scribe with your tool of choice, I used a Dremel w/ cut-off wheel.
Again I forgot to take intermediate pics but you get the idea. Remove the paint and clean up the cut with a grinder. It was necessary to flatten the blade as it had a slight cup. Flattening can be done on a belt sander, disc sander, or 80 grit sandpaper glued to a flat surface. The blade doesn't have to be perfect but the flatter it is the better it will slice wood. Also flatten the top as this will be one cutting edge.
Cut 2 pieces of scrap wood approximately 5" x 2 1/4" x 3/8", the exact length and thickness is up to you. Drill a hole for the binding post which will fit through the existing slot in the blade. Drill a hole and countersink on the opposite handle for the machine screw. Secure the handles to the blade with epoxy or CA glue and secure with the binding post. If the screw protrudes on the back just grind it flush. Sand the handles flush to the top and bottom of the blade and apply a coat of oil or your finish of choice.
I didn't bother polishing the blade.
It's ugly. If I were to do this over I would cut the blade to 1" wide because it doesn't need to be this bulky. That said, I wouldn't bother making another. This one works okay and I use it but there are better options for homemade parting tools. A thinner blade generates less heat and is less metal to sharpen. Sometime soon I plan on making a parting tool from an old carbide saw blade.