Introduction: CNC Shopbot Geneva Wheel
I'm working on some demonstrations to teach mechanical engineering concepts to 11 - 17 year olds.
The first item that I decided to build was a Geneva Wheel. I made mine using a Shopbot.
The Geneva Wheel or Maltese cross is a gear mechanism that translates a continuous rotation into an intermittent rotary motion. The rotating drive wheel has a pin that reaches into a slot of the driven wheel advancing it by one step. The drive wheel also has a raised circular blocking disc that locks the driven wheel in position between steps.
The name derives from the device's earliest application in mechanical watches, Geneva, Switzerland being an important center of watchmaking. The Geneva drive is also commonly called a Maltese cross mechanism due to the visual resemblance when the driven wheel has four spokes. Since they can be made small and are able to withstand substantial mechanical stress, these mechanisms are frequently used in watches.
They are also used in film movie projectors, bank note counters, and assembly lines.
Step 1: Draw the File in VCarve Pro
I drew the attached DXF file in Vectric (www.Vectric.com) Software so that I could cut it out on on a ShopBot Router.
This is a great link if you want to learn more about the math.
After I drew the file, I cut it out on a ShopBot
This is what it looks like when it is working: http://youtu.be/INhvmcU-4Ks
Step 2: Glue It Togehter
The trick in getting the Geneva Wheel to work is that you need to have the half-moon orientated correctly so that it appears as the one being held by the two vice grips.
Other than that, you need to make sure that you don't glue the axles (5/16" birch dowel rods) to the rotating parts.
This is a video of the shopbot cutting out the file out of 1/2" MDF. http://youtu.be/QCWB2caoTkk
I made it at TechShop!