I made this instructable because I needed a way to drive multiple axles in sync for another instructable I am making. Unlike some makers I have no access to any CNC machines and due to that, I cannot build custom parts easily. One thing I am fortunate to have though is a fairly nice wood working shop, not that you need a very nice one for this project. I have attached the link to the design in the 123D library for all those CNCers out there, but for everyone else you can make this with some simple tools. This sprocket can be used for mechanical purposes, or it can be used for art and decoration.
-a hand saw (or a table saw that can cut 45 degrees)
-a drill (I used a drill press, but a drill will work)
-a 3/4 inch drill bit
-wood thicker than 1/8 in (plywood will splinter easily)
-an accurate ruler or measuring tape
-a clamp or two
-a metal file or sand paper
-SAFETY FIRST! safety glasses
lets get started!
Step 1: Squaring
First, you need to cut a square out of the wood. This square should be 2.5 in x 2.5 in. Make sure it is as close as possible to being right on. The problem with this whole project is that with an octagon, in order to make one with one inch sides from a square you need the dimensions to be 1+(2/(sqrt2)) which is unfortunate because nobody makes 1/sqrt2 rulers. Fortunately 1/sqrt2=.707106... which is very close to 3/4 or even closer to 11/16. I used 3/4 which is why the square is 2.5.
Step 2: Octagonalizing
This is where precision really starts to matter. Measure 3/4 from a corner of the square on both edges, then cut from point to point. Repeat that for each corner. Do not be afraid if your octagon doesn't look quite right, the measurements are not perfect, so it is a little off.
NOTE: disregard the drilled out portion of this picture
Step 3: Drilling
Here is where you will use your drill/drill press and 3/4 inch drill bit. Take your octagon, clamp it down tightly and drill straight down centering your drill on the octagon's vertices. Be careful to clamp it down well, because a 3/4 drill bit will rip that piece of wood right out of your hands. Precision really matters here, because if you are a little off, your sprocket may not work.
Step 4: Sanding/Filing
With your file or sand paper, round off the teeth on your sprocket. After that, your sprocket is done. This picture is a perfect example of what happens when you use plywood, it splinters a little.
Step 5: Drive Belt
In order to actually use a sprocket, you need a belt. You can make a belt out of almost anything, the only thing you need to know is that 3/4 the length of your octagon's side is the spacing from the center of one hole to the next on the belt, or in the case of the sprocket I built, 3/4 in. I included a picture of my quick paper belt.
Step 6: Why Use a Computer?
I used a computer to produce a prototype because I was not sure that my idea would actually work. I needed to see if the octagon would actually turn out the way that I wanted to. It also gave me what measurements would actually work (i had a couple pages of calculations for ideal measurements).
I used 123D which is great because it is free and easy to use, my next project, which is a secret for now, will also be constructed in that program. I encourage all makers to at least learn how to use CAD(computer aided design) programs as it will come in handy.
Step 7: The Future
Since I have entered this into the make it challenge I feel that i should say what I would do with a 3d printer. I often find myself at the point in a project where a part is almost impossible to make without such a machine, and although this does take me down a path of discovery, it often leads to distraction and loss of focus and dedication. I have a number of projects in mind for the near future, one of which will be an entry in the robotics challenge (it will probably appear in a month or so), and a few others. Happy making my friends, I hope you found this useful.