1. Unlike belts they can transmits large amounts of torque
2. Unlike meshing gears they don't need to be constantly lubricated
3. Unlike belts and mesh-gears the spacing between gear centers can be easily adjusted by shortening/lengthening the chain
However, getting the right size/right pitch gear can be an impossible task for some DIY projects. Specifically, those that require a gear to fit a certain bolt mounting bolt pattern.
The obvious solution when a sprocket gear is wanted, but can’t be found, is to make your own. Historically, this is easier said than done because the two main methods for a DIY to create the high accuracy needed for a sprocket gear is to use a 3D printer or plasma CNC. Both of which have issues given that sprocket gears typically require more strength than can be provided by 3D printers and the warping often caused by plasma cutting creates gears that have an annoying tendency to throw the chain off.
This is where plasma-sprockets enter the scene. I developed these while creating the world's first apocalypse ready solar car, the Apocalypse EV1 (http://www.ApocalypsEV.com). Plasma-sprockets use a radically different multi-piece sprocket design. The unique design sandwiches a chain between two side sections as it rotates about the gear, preventing any warping issues caused by using a CNC plasma cutter.
In addition to creating sprocket gears that can be effectively cut with a CNC plasma table; plasma-sprockets do what no other gear or pulley has done before - allow you to take them on and off the middle of an axle without having to take the axle off. By not having to remove the tires, bearings, and mounting brackets just to change a gear ratio, plasma-sprockets save hours of time and lots of confusion (trust me).
This Instructable covers how to create a virtual plasma-sprocket and then make it into a real part via a plasma CNC table.
Step 1: Get DraftSight or other 2D CAD
For those who have learned how to use, and are hopelessly addicted to AutoCAD's GUI, I might note that DraftSight has the look and feel of classic AutoCAD without the $4000+ price tag.
NOTE: This instructable only covers how to convert an already drawn sprocket gear into a plasma-sprocket. To learn how to draw a basic sprocket gear and where to get a free CAD program please check out one of my other instructables that covers the topic http://www.instructables.com/id/How-to-Draw-a-Sprocket-Gear/.