Summary

This modification will greatly reduce or completely eliminate your z wobble issue, and it will only cost you about $3.

Instructions

This modification has reduced my z wobble to nothing. The M8 leadscrews are far too stiff and will affect the X carriage in unwanted ways. 10-24 threaded rod is much more flexible and will affect the X carriage much less.

Vitamins you'll need for this modification are two 295mm lengths of 10-24 threaded rod, eight 10-24 hex nuts and two 10-24 washers, two compression springs that will fit over the rod, and four short lengths of 1/8"ID 1/4"OD vinyl tubing. For the clamps you'll need eight M3x20 screws and nuts or 4-40x0.75" screws and nuts.

Print four of the 10-24 to M8 adapters and two sets of the coupling clamp.

Slide 10-15mm piece of vinyl tubing onto the end of your stepper shaft and another piece onto the end of the threaded rod.

The side of the rod with the vinyl tubing is the top.

Press the 10-24 hex nuts into the 10-24 to M8 adapters, screw one adapter onto the rod with the 10-24 hex nut facing up, slide the spring over the rod and insert the rod and adapter into the x carriage support. Compress the spring and screw the other nut adapter on the rod with the 10-24 nut facing down, screw up into the x carriage support so the spring has some compression on it. Screw on two additional 10-24 nuts and then a washer and tighten the two nuts together at the base of the z lead screw.

Your new z axis steps per millimeter is 3023.62 steps/mm assuming you are using 16x microstepping.

You can see my before and after z wobble form the picture of the blue pink panther woman and the red cylinder. The pink panther woman was one of my first prints and you can see considerable z wobble, the red cylinder was my first print after the modification and you can see there is practically zero z wobble.

The patriotic red, white and blue pink panther women are all printed with pla. The blue one was printed before swapping my lead screws. The white one was printed with the new lead screws with some white pla that I believe had absorbed to much moisture and has some serious layer smash issues. The red was printed with the new lead screws and also has some layer smash issues but the z wobble is obviously greatly improved from the old M8 leadscrews.

These parts were made in SolidWorks and repaired in Netfabb to ensure they are perfectly manifold.

Prusa Mendel Zero Z Wobble Upgrade