ACME Z-axis (SO1)

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Upgrade Name: ACME Z-axis

The ShapeOko 2 utilizes slightly different parts, see photos by User:Improbable Construct in ACME upgrade pictures for NEMA 17 install.


Created by: User:Improbable Construct

Description: An upgrade that replaces the M8 threaded rod with a 3/8"-12 Acme Screw.

Status: Fully functional


  1. Increased speed, 12 TPI(ACME) vs. 20.32 TPI(M8 rod).
  2. Increased strength, threads are broader and squarer than M8 threads.
  3. Increased accuracy, ACME screws are made to tighter tolerances than threaded rod. This is especially an issue as regards straightness --- Acme will spin truer resulting in less vibration.
  4. Better support, Z-Axis supported by the bearing blocks, not by the stepper motor and coupler.


  1. 1x 3/8-12 Acme screw 200mm of threads turned down to 8mm on both ends.
  2. 1x Delrin ACME nut
  3. 2x Bearing Blocks / Motor Mounts
  4. 2x 608 Bearings
  5. 4x M5x20 socket head cap screws
  6. 4x M5 washers
  7. 1x 8mm shim washer

Cost: $75.00 for the kit ACME screw Z-axis upgrade for Shapeoko


Discussion in the forum

Play both videos at the same time to compare threaded rod vs. ACME screw.

This is what is in the kit:

ACME Screw, Delrin Nut, Bearing Blocks, and Hardware.


Step 1

Remove your spindle
Remove the Z-axis
Don't forget to disconnect the motor wires.

Remove Z-axis.JPG

Step 2

Disassemble the Z-axis

Disassemble Z-axis.JPG

Step 3

First, you should test-fit the assembly to see if you will need the shim washer.
Position the bearing blocks at either end of the Makerslide with the ACME screw captured between them.
Using the included M5x20mm screws and washers, attach the top and bottom bearing blocks to the Makerslide.
The bearings should both face the Makerslide.

Test assembly.JPG

Check to see that the ACME screw is securely captured between the bearings.
If there is any movement, add the shim washer to the longer of the turned ends and recheck.
If there is no movement, do not add the shim washer.

Shim washer.JPG

Step 4

Remove the top bearing block from the Makerslide and remove the ACME Screw.
The top block is the one with the longer of the turned ends in it.

Hey! That's the same picture as the one in step three! Would it be so hard to take a new picture? -IC

Remove the coupler from your stepper motor.
Measure the length of your stepper motor shaft.
If it is less than 20 mm you can move on to step 5.
If your motor shaft is 20 mm or more you will need to cut the ACME screw down a bit.
Use a saw with a metal cutting blade to cut 10 mm off of the longer end. (Alternately, measure how much to cut by dry-fitting everything but the motor, then align the motor w/ the ends of the spacers and note how much the shaft and rod overlap --- cut off that much plus length of the spring area of the flexible coupler --- the shafts should not reach all the way into the coupler so as to allow it to flex w/o wear and stress)
If the acme rod is cut at a slight angle or if it is not exactly 10 mm it will still work fine since its going in the coupler
Depending on your cutting method, a bur or lip may have been created in which case your acme rod may not fit back into the coupler. If this happens, simply use a file to chamfer the edge of the acme rod. Or, use a dremel and grinding wheel

Step 5

Attach the Delrin nut to the universal plate reusing the stock screws and washers.
If you are using insertion nuts to hold your spindle mounts, now would be a good time to slide them into the Makerslide.

Assembly 1.JPG

Step 6

Slide the coupler back onto your stepper motor.
Attach the new top bearing block to your motor using the stock bolts and spacers.
Slide the universal plate onto the Makerslide and insert the Acme screw into the bottom bearing

Assembly 2.JPG

Step 7

Slide the bearing block and motor assembly over the ACME screw inserting the ACME screw into the coupler.
Attach the bearing block to the Makerslide using the included M5x20mm screws and washers.

Assembly 3.JPG

Fine tuning

To make sure the mounts are aligned properly, you need to fine tune your bearing block placement.
Turn the ACME screw until the universal plate is all the way at the top.
You may have to loosen the top and bottom bearing block screws and the Delrin nut screws to get it to turn easily.
Once you have it at the top, square the top bearing block and snug the bolts down.
Turn the ACME screw until the universal plate is at the bottom. It should turn easily.
Once you are bottomed-out snug the bottom bearing block bolts.
Repeat this process until the universal plate travels easily along the Makerslide.
Once you can easily run the universal plate up and down the Makerslide tighten the top and bottom bearing block bolts.


Re-install the universal plate to the X-axis motor plate.
Connect your motor wires.
Attach your spindle.

Calculate your new steps per millimeter

To calculate steps per mm you need to know:

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

So 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 (or $2=377.893 for 400)


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