Foam Board Miter Cutter

thingiverse

I needed a 45° cutter to make miters in some 5mm foam board without cutting right through it. It was a 30-minute design and a 40-minute print, so the end result is a bit rough and ready but does the job I needed it to do. Pics of the thing in use and also the flash diffuser I was making are shown above. All you need to do is draw a line on the center of the joint you want to make (on the inside of the fold, obviously). Position your rule/straight edge along the line and carefully draw the blade through the board while keeping the front edge of the cutter against the rule. Do the same on the opposite side of the line, and you'll have a small wedge of foam to discard and a neat 90° rebate allowing you to fold your board. It takes a standard Stanley/Box Cutter blade, the type that are 62mm across the sharp edge. If a different size blade is used, it may not work as intended because the amount of blade sticking out beneath the base might be different. I just hold the blade in place while using it, although you could tape it down if you prefer. Please note: The 5mm version in the example photos is the only one I've tried. The other two (for 3mm & 10mm foam board) are the same principle and should work. I have no need for these thicknesses, but a comment on my Reddit post asked about making a set of them. If you try them and they work (or even if they don't), please leave a comment. Also: Obviously, these types of blades are ridiculously sharp, and care should be taken at all times while using them. I can't accept any responsibility if you use these cutters and hurt yourself.