I made a 2.5up...but I need spare parts!!!

[Mooselake]

The problem using test cubes (or any other print then measure) calibration is that you're looking at multiple variables. Besides axis steps per mm you have variable width extrusion, so while you may be able to make a 1.000 inch cube a 2" cube will be off, as will any other size.

The best method is using factory produced pulleys, screws, etc. For 3D printed parts (which can be out of round besides off diameter) using a dial gauge to measure movements is more accurate (one variable only, axis movement per step), then separately calibrating your extrusion width.

This argument (the multivariate situation) was a big deal back when 3D printers were mostly printed parts, when measuring was your only choice. These days when most printer parts are molded/cast and machined in some giant factory their tolerances are beyond what most of us can measure, although there are a few guys out there with access to a metrology lab (run into a couple...) that can better what we mere mortals can do. And in the end they usually differ by a few parts per thousand or smaller. This puts them in the range of thermal expansion and contraction...

My one up (partial compensation for the RPM mess) never had enough working parts to be worth assembling so the usable bits went into the spare parts box

Kirk