Summary I also designed one with a built in belt tensioner http://www.thingiverse.com/thing:1674146 This is a modified mount for the Max Micron Prusa i3 clone (probably fit many others also) shifted the stop switch over and away from the mounting bolt so they don't interfere with each other anymore, also in sunk the mounting bolts so once started no need for twisting around and trying to keep a wrench on it while also trying to turn a driver for the bolt. more solid design also for strength .