ZeroG Hydra Oldham Coupler & Thrust Bearing Mod

I created this on a user request. At the moment, this is untested! 

This mod adds F8-M16 thrust bearing blocks to Sir_Washes Hydra Oldham Coupler mod.

Stepper motors are not designed to take axial load. With the weight of the bed pushing down on the motors, there is a high risk that the spring washer inside of the motor gets compressed causing uneven layer heights or even cause damage to the motors.

With this mod the weight of the bed is no longer pushing down on the motors but rather on the bearings and the motor mounts.

Use rigid couplers instead of the commonly used springy ones as the goal here is to remove any vertical wobble.