1) Get 3 cards – 1 normal credit card (preferably expired), one card that is not a credit card (because they are not flat), but has a magnetic stripe on the back, and a 3rd card that is of the same size, but does not have to have any markings (could be an old drivers license or company keycard, for example)
2) Get a snap-knife blade of the slim type (also known as a “Japanese Knife” blade).
3) Cut the 3rd card to shape as is illustrated in the image. The idea is that the hole in the blade will be secured using an axle and when rotated, will protrude down about ½ of an inch.
4) Cut the bottom card (no. 2) as is illustrated in the image. This hole will be used to extend the knife, and hold it in place.
5) Cut a hole in the 1st and 3rd cards, about 1/16” wide. Try to make the holes exactly above each other. This will be used to hold the axle that holds the blade in place.
6) Using simple contact glue, glue the bottom card (no. 3) to the middle shape (card no.2). Try to make the gluing as clean as possible, with no glue traces on the contour lines.
7) Place the blade in the cavity that’s in the 2nd card.
8) Glue the top card (no.2) to the middle one, and again – try to make it clean.
9) Use a piece of soft plastic as the axle, and insert it through the top hole, the blade’s hole, and the bottom hole.
10) Cut the axle so that it protrudes only about 1/16” to each side.
11) Using something hot, push on the axle’s ends, and flatten them. This can be done with a soldering iron, but works just as well with a large nail’s head, heated over the stove-top. Ideally, the outcome will be an H shaped axle, as flat as possible on the credit card.
12) Now, use your finger to push out the blade and hold it in place. Practice extending it quickly and holding it steady. Keep in mind that the blade is really sharp, and if you keep the knife in your pocket or wallet, it has no safety and can extend and cut the wallet or wound you.
