I made this a while ago and have second version that had inproved pin so it would be easier to print but I can't find it now.

I used to make knives back in the day and kinda miss it and I don't have the space and tools to make steel ones so I designed this little keychain knife from scratch to be easily 3d printable in 3 parts that easily click together creating little slip joint (non-locking) knife.

About practicality. I made this as a keychain to put on my keys and show people what you can 3D print, open letters and cut the tape on boxes once in a while. Blade retention and durability depend on what materials you use. If you by any chance have a machine that 3d prints metal you can have a fully functional knife and you can get some fairly nice results with carbon fibre or metal-filled filaments but it will be nowhere near the same as if it were hardened and made of metal. If you use PLA it's pretty much just a letter opener.

As you can see in the background of my pictures I made a lot of them making sure that it is as good as they can be it is a fairly small thing so if your printer isn't set up that well I would suggest you scale it up a bit first.

I will try to add in a short video with a timelapse of it being printed and the final assembly just in case. Again I have it somewhere but not sure where.

Disclaimer if you decide to purchase this file you are the one responsible for a physical product you create from it. As for me posting this, I am not aware of any place where it would be illegal to print a knife but I don't know everything. From what I know I can tell you that although it is just an innocent keychain/toy that can hardly cause any damage there are countries with strict rules in which this item could be classed as a knife or a weapon and therefore illegal to carry in public places and I would strictly advise anyone to NOT take this on a plane.