Personal Over-engineered Kinetically Extending Digit (POKED)

This project started as an exercise for me to learn to design mechanisms. I ended up spending way too much time on it (most of which spent coming up with a name) and, since perfect is the enemy of good, I had to declare it done. In the end it is a fun toy to play with, it is oddly satisfying to use, and it makes a great conversation starter if you leave it on a table when you have guests at home. Don't use it to poke people in the eye.

For this project, I am assuming you're already familiar with how to use a laser cutter. If that is not the case, I would recommend reading this Instructable and/or asking people at a local makerspace. You could also use an online laser cutting service, but since I've never used one, I can't make any recommendation.

This project requires quite a lot of hardware :

•    A 200 x 200 mm minimum 6 mm thick wooden board suited for laser cutting (I use MDF, but plywood works fine too)
•    17 M3x20mm screws
•    1 M3x25mm screw
•    54 M3 washers
•    18 M3 nylock nuts (regular nuts won't work as these get loose when using the device)
•    A piece of Ø 3 mm interior/Ø 4 mm exterior diameter brass tube (an M3 screw should fit inside)

As for the tools, you will need:

•    Access to a laser cutter
•    A screwdriver that matches the head of your screws
•    A pair of pliers
•    A hacksaw
•    A file

The design file comes in two versions : lefty or righty. These are basically mirrors of one another, so you can flip the parts around after cutting if you chose the wrong one, although I wouldn't recommend doing so as laser-cut parts often have a side that ends up cleaner than the other.

Since I am left-handed, the pictures in this Instructable are for the lefty version.

After choosing a file, load it into your laser cutting software. The lines are split into three groups: the etching of the hand, the holes and the outline of the parts. Make sure you set your laser cutter to do the etching and the holes before cutting the outlines, as this will prevent the parts from getting misaligned during the cutting process. If you prefer setting the order of the cuts yourself, I have also provided SVG files for each individual parts.

After cutting, you should have:

•    Two parts of the handle
•    The etched hand cutout
•    Ten linkage bars
•    A small round spacer

To reduce friction between the screw and the wood, you will need a brass bushing that will fit inside the slot on the hand cutout. Using a hacksaw, cut a 6 mm piece of brass tubing, and smooth out the ends with a file. It is fine if your bushing is a little longer than 6 mm, but don't cut it shorter than the thickness of your material or the bolt will be too tight to move freely.

With a screwdriver and a pair of pliers, attach the two parts of the handles using a 20 mm screw. Use washers to "sandwich" each part and screw a nut at the end (check the diagram for reference). Pay extra attention to the way the handles are put together : the smaller part goes on top! (Note: this is true for both the left-handed and right-handed version)

When tightening the screws, make sure that the parts can move freely without too much wobble.

Assemble the ten bar-shaped parts of the pantograph mechanism using the same procedure as before. To keep things organized, start by assembling each pair of bars before putting them together along with the handles. Remember not to tighten the bolts too much!

These last two parts are the trickiest, so check the pictures for reference if you have trouble putting everything together.

Use the 25 mm screw to attach the top of the hand cutout to the rest of the assembly. Place a washer, the round spacer, and another washer behind the hand cutout before inserting the screw into the hole at the top end of the pantograph mechanism.

For the sliding joint at the bottom of the cutout, add a washer and the brass bushing around a 20 mm screw before passing it through the slot. Put another washer, and pass the screw through the bottom end of the pantograph mechanism. Add another washer and a nut at the end and tighten the screw.

Once everything is assembled, check that all the parts can move freely. If the mechanism gets stuck, unscrew the bolts a little.

And that's it, have fun !