Stop! Read this!

Update 29 Sep 2021: I've had a couple of these fail. Thankfully they didn't fail in a way that caused injury, but I've come to the conclusion that this design is neat, but it's just no good for a printed item. It's possible it could be beefed up, but I've found that sometimes just because you can print something - it doesn't mean you should. There are plenty of nice razor knives you can buy made out of actual metal, I strongly suggest you buy one of them instead of trying to print one. Because of this, I'm taking down the files for this design. If you insist on printing a razor knife, check out the sources and print one of those.