Concept: Janus' Ring - The fastest folding Knife ever

DISCLAIMER:

I'm not responsible when you hurt yourself or anyone else with this thing.

This is just a box cutter knife you can't misplace anymore…

Yeah I know professional box cutter users don't misplace their knife because they have the routine to place them back in a pocket but I'm just a occasional user and somehow I misplace them all the time... so I came up with this completely revolutionary new knife design.

It doesn't have a traditional handle! It's attached to your hand like a ring all the time, that's where the name comes from: the ancient Roman God Janus. He is usually depicted as having two faces. This means your hand is free to do anything else like typing on a keyboard like I just do or reaching for the bear spray in your pocket or whatever you may wanna do. The knife is kept close with a magnet. It opens on a very specific but very subtle hand movement and also gets fixated with magnets in open position. (I wouldn't call it a lock because there is nothing to press / slide to unlock it again.)

Check out this video: https://vimeo.com/886777874 (14 seconds; just showing the opening and closing multiple times from different angles)

It's designed to be build as easily as possible and requires only off the shelf items:

• 1-3x 9mm break-off box cutter blades (as many as you can stuff into the holder to make them fit tight). BE EXTREMELY CAREFUL WHEN DOING THIS. YOU WANNA MAY USE PLIERS!
• 3x 5x1,5mm magnets. (can be obtained from GIZEH cigarette rolling papers which should be easily sourceable worldwide) ((you could get away with only one magnet but it's definitely way more fidgety with three of them.))

This is obviously a prototype and therefore FEEDBACK IS HIGHLY APPRECIATED!

I have uploaded a couple variations of the ring size for you all to start and experiment with. If anyone wants to do a openscad version feel free to do so.

The first number in the filename is the diameter of the index finger and the second number is the ring finger in mm.

Sidenotes:

• This design turned out to be the fastest deployable knife in the world.

Why? Well, you don't have to reach for it in your pocket anymore because it's a part of your hand. It's always ready within milliseconds and just half an inch of hand movement away from being deployed. Your reaction time is the only time it takes to deploy it. 

• For fidgety reasons you could use two of them on one hand or four on two hands. START WITH ONE. BE CAREFUL!

Printing:

• Print it laying flat on it's side. It will need (tree) supports. Make sure the supports don't jam the hole.
• Make sure the two thin walls get sliced properly. (one wall on the ring and one on the bladeholder - it's part of the magnet housing)

Printing suggestion:

use transparent material for the blade holder to show off the whole shiny blade and make it appear as it would be floating in mid air ;)

Assembly:

• deburr or drill the M3 hole to a size that the printed axle or a real M3 screw will move absolutely freely in it without any friction on the ring part. don't touch the two holes on the bladeholder part. the axle is a press fit into the bladeholder part and the ring part moves freely on the axle.
• pressfit one magnet into the tiny square hole on the ring part. should be nice and tight if it's not use glue. (the magnet is bigger in diameter then the ring is thick. 4 vs. 5mm. so make sure the magnet sticks out 0,5mm on each side. thats pretty crucial or the whole thing can't move freely.
• take a second magnet let it place itself against the other magnet from the outside of the ring. pull it off and mark the side thats attracted to the other magnet. take the bladeholder part and pressfit the magnet from the flat side (bottom) into it. watch out for correct orientation. (the marking you did has to face towards the axle.)
• brake off three pieces from the blades you want to insert. insert the blades into the holder. check orientation or make it two sided. be extremely careful!
• let the parts snap together. the three holes on the two parts should line up. shove the axle / M3 screw through the three lined up holes.
• The third magnet goes into one of the four possible positions between the rings to hold the blade in place when closed. I made several positions for you to experiment with. I use the third position.

Be vigilant and don't forget to post your make and leave a comment!