Zaxis ACME

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Completed ACME lead screw installation
Lower ACME bearing plate mounted

Z Axis ACME Lead Screw Upgrade

What's in the Upgrade Kit

  • 1 x 3/8" (bad ass) acme screw with machined ends --- turned down to 7.92 mm diameter to fit into the bearing. One end has 7 mm turned down along its length the other end has 30 mm turned down.[1]
  • 2 x Z-Axis Shim Plates (modified to fit flanged bearings)
  • 1 x Flanged Bearing
  • 4 x M5 x 16mm Socket Head Cap Screw
  • 4 x M5 Flat Washer (black!)
  • 1 x 8mm Shim Washer
  • 1 x 3/8" acme lead nut (single start)
  • 3 x M3 x 8mm Socket Head Cap Screw (not pictured)
  • 3 x M3 Flat Washer (not pictured)

ACME Lead Screw Assembly Instructions

  1. If you haven't already done so, tap the bottom of the Z axis maker slide to accept the M5 screws
  2. Install the included flanged bearing into the lower rounded bearing plate. Be sure to press the bearing evenly on all sides until the flange sits flat on the plate all around.
  3. Place 1 M5 flat washer on each of 2 included M5x16 SHCS
  4. Attach the bottom plate with the flange of the bearing facing up to the makerslide by placing one of the included shims plates between bearing plate and the makerslide. Screw the assembly together using the two M5x16 SHCS from step 2
  5. Install the lead screw with the delrin nut attached into the lower bearing
  6. Install the flanged bearing included with the original SO2 kit into one of the original Z axis top plates
  7. Place 1 M5 flat washer on each of 2 included M5x16 SHCS
  8. Slide the top plate and bearing over the top of the ACME screw with the flange of the bearing facing down
  9. Attach the top plate to the makerslide by placing the second of the included shim plates between the plate and the makerslide. Screw the assembly together using the two M5x16 SHCS from step 6

Forum post with detailed pictures from Improbable Construct

Check for play in the lead screw. If there is too much vertical play, remove one of the plates and install the included 8mm shim washer onto the lead screw and reassemble. This should be sufficient to remove any vertical play.

Now you will want to tune the lead screw so it spins easily. Slightly loosen the screws on the bearing plates and shift the plates slightly until you are able to freely turn the screw. Tighten one screw at a time and verify that the lead screw still spins easily. Continue until all 4 screws are tight and the lead screw still turns freely.

Updating Software

Calculate your new steps per millimeter

To calculate steps per mm you need to know:

  • Steps per revolution of your motors (normally 200 or 400)
  • Microstepping of your controller: 1, 2, 4, 8, or 16
  • Thread pitch: The ACME screw is TPI = 12 or pitch = 2.117

The math is: Steps * Microsteps / Pitch = Steps per mm

  • Ex: 200 * 2 / 2.117 = 188.946623
  • If you are using grbl then:
    • $2=188.947 for 200 step per rev motor (the default)
    • $2=377.893 for 400 step per rev motor


  • Enter your new steps per mm into your control software.
  • Enjoy your faster, smoother, and stronger Z-axis.


Post discussing dimensions and possible difficulties and solutions: Re: ACME screw upgrade for Shapeoko Z-Axis.

Source files

bottom bracket.dxf[2]

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