The Rack Gear (16-pack) is now available for purchase on www.vexrobotics.com - P/N: 276-1957 - $19.99
Rack gears can be used to turn rotary motion into linear motion.
*]Use any VEX spur gear as a pinion to drive these rack gears.
*]Stack multiple rack gears back to back for longer motions.
*]Combine these with a VEX linear slide and Rack Gear Bracket (sold separately) to create a simple linear actuator.
*]Each Rack Gear includes (3) 6-32 threaded inserts on their back face. Mount these similar to VEX motors or servos with 6-32 screws.
In my experience, chipping the rack gear teeth is mostly because you didn’t get a good, tight mesh between the pinion and the rack. If you are using the linear slides with the bracket, you can adjust the clearance between the pinion and the rack by adding washers between the gearbox bracket and the sliding rail. If you think this through, you will see that it moves the pinion gear CLOSER to the rack, reducing play and chipped teeth. Of course, this can also introduce more friction so you may have to play with the tolerances.