Safety knife
thingiverse
A versatile safety knife/cutter is this one: https://www.martor.com/it/prodotti/coltelli-di-sicurezza/product/secumax-combi-109137.html. It's incredibly easy to print and operate. Just two files are required: the main body and the top section. Print them out, insert the blade, and then attach the cover. To seal it securely, you can even add a screw to the top.
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With this file you will be able to print Safety knife with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Safety knife.