Tevo Tarantula Dual Z / Adjustable Z Limit Switch

A simple and minimal inverted single-motor dual Z mod for Tevo Tarantula. It's easy to print and effective.

• Before assembling, make sure both rods (lead screws) are straight. If not, it's better to buy new rods rather than compensating for it or resorting to suboptimal solutions.
• Key to zero rotational backlash is to properly tighten the belt by adjusting/sliding the secondary rod.

The calibration cube was printed @0.1mm layer height with properly tensioned belts https://www.thingiverse.com/thing:1780636

I tried to fix the following problems in the original design:

1. The X axis can be pushed up and down, which can be problematic especially for auto bed leveling with constant z motion. This is due to the flexible coupler and the bending of the acrylic mount of the Z motor. This design inverts the placement of the motor, which allows the lead screw to sit directly on the motor shaft inside the coupler. This completely prevents any downward push and get rid of the top acrylic bending problem.
2. Both rods are locked in place with pillow block bearings, which prevent the x axis from rotating like in the original single rod setup. I prefer the single motor solution because the two rods are always in-sync and I can manually turn the z motor without resyncing.
3. An adjustable z axis limit for quick fine-tuning the height.
4. Both rods are positioned much closer to the X axis (Photo 4) to reduce the bending torque exerted on the top rod mount (or the original acrylic motor mount). And the top rod mounts are reinforced so that there is minimal or no bending.
5. The nut mount design allows the x axis to rigidly sit directly on the brass nut of the lead screw to prevent any bending torque and vibration (Photo 4). Both 4 and 5 help prevent banding.

Part list:

1. 400mm Lead screw. http://www.ebay.com/itm/322001200138
2. GT2 Timing belt 696mm. http://www.ebay.com/itm/2GT-Timing-Belt-L-520-540-550-600-606-610-640-670-696-GT2-synchronous-Belt-loop-/331976368563
3. Flange Bearing Pillow. http://www.ebay.com/itm/1Pair-8mm-Bore-Diameter-KFL08-Pillow-Block-Bearing-Flange-Rhombic-Bearings-New-/232076410895?hash=item3608d5000f:g:KtMAAOSwxg5X0ndu
4. Timing pulley Bore8 OD16. http://www.ebay.com/itm/5PCS-lot-GT2-Timing-Pulley-20T-5-8mm-Bore-FOR-6mm-Belt-Reprap-3D-printer-CNC-/131816900256?var=&hash=item1eb0e646a0:m:mN8y5RI51dnaKfVrGeEKEyA
5. M3 T nuts. **This is M3 not M4. http://www.ebay.com/itm/50-x-20-Series-European-T-slot-Aluminum-Profile-Carbon-Steel-Drop-In-M3-T-Nuts-/152016284528?hash=item2364e06b70:g:cucAAOSwhMFXkzEX
6. M3 screws, M4 screws, M4 nuts.

I attached the original fusion 360 file for educational / modification purposes (please excuse the mess) E.g. you may want to change the hole to fit M4 with M4 T nuts instead.