Summary

Here's a hand tool for making miters and chops in small materials. Good for model building, doll house trim, etc. It uses a common utility knife blades and 4-40 screws. The model is in inches so scale by 25.4 for Millimeters if necessary and the knife blades will fit well.
7-9-15 Update- I accidentally exported with too high a resolution for the geometry. The files now are much liter.

Instructions

This is a chopping tool and it works really well!
It uses 3 screws, 4-40 that are 9/16" long. I bought them online, but you can drill out the holes if necessary to fit what you have on hand. The model also uses utility knife blades that are available at any hardware store. The model is in inches so scale by 25.4 for Millimeters if necessary and the knife blades will fit well.
The uploaded model is a little more deluxe than the photo, so you benefit from the second version.
I made two different lengths of hold down dogs. I like the short one because it is so sturdy, but there may be a use for the taller one in some instances. I recommend roughing up the surfaces where the dogs go inside the holes, inside the holes, the miter guide, foot of the dogs, and the surface of the chopping block. A little sandpaper abrading helps pieces not to slide around. If you haven't used dogs before, just put the end in the hole and press down until it wedges. A slight twist and pull will unlock it. I wouldn't recommend leaving them wedged after use because it may distort the plastic.
If the cut doesn't go all the way through, you can move it to the end of the razor by where your hand presses to try again or prop the piece up with a little material under it. You can draw other angles on the bed to line up with and use the dogs to hold the material in place to cut.
If necessary, you can model a mitered piece to prop and chop crown molding for doll houses.
Enjoy!
Simonarri on Instagram.

Miter Razor