For this Instructable I made a 3D-Printed Geneva Drive, which is a mechanism that converts constant rotational motion into rapid, indexed motion of a certain number of degrees. This is really hard to visualize, even from pictures, but Wikipedia has a great animation here: http://en.wikipedia.org/wiki/Geneva_drive . I originally made this Geneva Drive to be a present, but I ended up not needing to give it away, so I keep it around as a cool engineering project. I designed it in SolidWorks from pictures of Geneva Drives online, and had it 3D printed by Shapeways. You can see a video of me rotating it by hand here: http://www.youtube.com/watch?v=XuHOVUXu2yE
Step 1: Why Are Geneva Drives Useful?
Step 2: SolidWorks
I love using Solidworks whenever I have the chance. I designed both parts in SolidWorks, making sure to design them so that they would fit together and work properly. I couldn't find any specific equations in Machinery's Handbook for designing Geneva Drives, so I looked at pictures online and designed the parts so they would fit together and operate the way I wanted them to. I then scaled them so that they fit within my price range, because 3D-printed parts are charged by the cubic centimeter of volume of the part.
Step 3: 3D Printing
This step was really cool, I had known about 3D printing for a while but this is the first time I actually had parts printed. I went to the Shapeways website: http://www.shapeways.com/ . They offer a wide range of materials, ranging from white plastic, which is $1.50 a cubic centimeter, to sterling silver, which is $20.00 a cm^3. I went with the white plastic, and tried to minimize the volume as much as possible, by cutting out as much material as I could from the back of the parts. On the bottom of the driving gear you can see that I cut some material away from the body and I designed it with some holes through some cylindrical parts of the gear. I designed it so that there was at least 1/8" of material everywhere, but I probably could have cut that down to 3/32" or 1/16". On the other hand, that little nub on the top of the driving gear used to be a little handle, but it snapped off when I had it in a bag I checked on an airplane. In hindsight, I probably should have made that handle a lot thicker and lower, maybe 1/4" in diameter and 1/4" high. The driver costs $18.81, and the driven part, which is called the maltese cross on there, costs $10.74. If you search for "Jared Humphreys" on Shapeways, you can view the parts on there.
Step 4: Wooden Base
This was a pretty easy step. To show off the function of the Geneva Drive, I drilled two holes into a piece of maple which were spaced apart so that the two parts would mesh properly. I determined the distance between holes by creating an assembly of the two parts in Solidworks and measuring the distance between the centers of the two parts.
Step 5: Functioning
The driving gear used to have a little handle on top, but it broke off, so now I have to rotate it by hand as best I can. You can see a video of it here: http://www.youtube.com/watch?v=XuHOVUXu2yE