Printable Anti-Backlash fixture for dual TR8 leadscrew nuts

EDIT:  Added a hexagonal version which should be easier to grip to tighten.

I was using a standard TR8 nut and leadscrew in my CNC machine and found it to have tremendous backlash.  The typical solution is to use an anti-backlash nut which uses a spring to push two nuts away from each other, but the spring is not usually designed for high loads, like a CNC machine would have. 

I posted about this in the StuffMadeHere discord, and Shane himself recommended this design.  I put it to the test and it worked perfectly!   It's basically a really strong spring (made from printed plastic) that you tune by tightening 4 screws.

I probably wouldn't use PLA or Nylon for this print.  They both have creep problems, especially at elevated temps (this design depends on compressing the plastic with screws).  ABS is ideal, PETG is probably fine.  

INSTRUCTIONS

See my video explanation here (link directly to 6m44s):

https://www.youtube.com/watch?v=VSWpaRQtn3E&t=6m44s

For my situation, the bottom nut is normally bolted to the core by itself.  So I would add the bottom printed part on top of that, and simply use longer M3 bolts to pass through both the printed part and the bottom nut.

To screw the top half to the bottom half you will need EITHER 4x M3 nuts OR 4x M3 heatset inserts.  

DIRECTIONS:

1. If using heatset inserts, put them into the bottom side of the bottom (blue) printed part that is facing the bottom nut.
2. Put the bottom lead screw nut into position
3. Put the bottom (blue) printed part into position, and use the longer M3 screws to anchor both the printed part and nut to the core.
4. Use short M3s to fix the top (green) printed part to the top leadscrew nut
5. Insert the leadscrew into the bottom half/pair.
6. Thread the top part onto the leadscrew
7. TIGHTEN the top against the bottom, with decent torque.  This will create a powerful force pushing the two halves away from each other binding hard enough that you can't spin the lead screw.
8. Gently secure the four tightening M3s through the slots in the top to the bottom holes (either directly into heatset threads, or fixed with nuts on the bottom).
9. Tighten all four screws very gently and slowly.   Try to get them to the same very light tension, then tighten each one a quarter turn and check if the leadscrew spins.  At some point, the tension in the screws compresses the two sides, and takes enough pressure off the nuts to unbind them from the leadscrew.
10. Once you can spin the leadscrew easily, you're done.  
11. Check a couple times over the next few days or weeks to confirm if they need to be tightened again, in case of creep