Nearly half a year since first log about dumping the Z counterweight, maybe increasing stiffness, and further reducing cost, here's the goods: Instructable; CAD.

This Z axis has hit the same micron (±0.8μm) more than 200 times in a row over most of an hour of Z probes in a "Minamil" rig (this project). Practical repeatability appears to be within 25μm (0.001") after warm-up. In other words, it can resolve micron-scale dimensional creep as stepper heat spreads through a structure.

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So how did that take half a year?

• June: #MRRFX and whY rethink Z
• July: Z v3: counterweight delete (& other wins)
• August: Z v3 -- counterweight delete -- progress
• September: ... still sorting Z axis repeatability ... (& Byproduct of debugging Z repeatability)
• October: Z v3 survives slow learning -- and a bonfire of time
• NovemberDecemberJanuary: writing the how-to very slowly

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Someone at Instructables apparently liked the 'ible enough to send it straight to the home page: