3rd Z-Axis Stepper Parts for D-Bot

thingiverse

This is a set of parts I designed and modified for D-Bot derived printers, adding a third z-axis threaded rod connected to a third stepper motor. The motor mount is a clone, matching the D-Bot's design as closely as possible, so printing another stock one would likely work fine. The bed mount is a from-scratch design that fits the stock threaded rod nut and anti-backlash nut, but moves the nut farther out from the bed to align properly with a stepper mounted below it. The nut can be mounted either inserted into the bracket or inverted, as seen in my photo, with room for the anti-backlash nut to fit in both cases. The whole setup can be mounted either inside or outside the rear rails of the printer, and I've tested it both ways, moving it to the rear to avoid potential snags from bed wiring. Many 3-support mechanisms on this site use toothed gears and belts to synchronize two or three threaded rods with a single stepper motor. While this mechanism works, it has significant drawbacks, including the possibility of a belt slipping and making it harder to get the Z axis back into alignment. It also leaves an exposed belt under the printer where things can catch on and potentially damage. Using a third stepper motor avoids these issues by driving all three rods equally. Depending on your controller, you may be able to run all three in parallel or serial off your controller, as I do with my Duet Wifi, running all three in serial. This design is forward-looking because it can accommodate a Duet2x or 5x controller and enable three-way active bed leveling, where the controller drives each Z axis separately to level the bed accurately. To keep the three steppers in precise sync long-term, I've calibrated the printer to re-sync them at power up. The basic pattern is to home all three axes first, then lower the bed 310mm quickly and reduce the stepper current to a very low amount. Next, it makes a slow additional move of 30mm, allowing the steppers to start skipping and sync back up above the mounts. Finally, it cranks the stepper power back up and rehomes the Z axis. For those interested in doing something similar, I have a corresponding part that bolts onto the top of the D-Bot motor mounts, including this one, which stops the gantry at precisely 40mm above the stepper motor mount. You can find it here: https://www.thingiverse.com/thing:2510053