calibration v calculation

I'm sorry, but I have to disagree with you on this one, this "hobbyist" is educated in this field, so grab a piece of paper and a pen. These are facts, not opinion. If you challenge these, cite your sources and we'll talk.

1) The step distance is a function of the number of and spacing between the teeth on the stator and the number of coils on the rotor, and you will never find a stepper that has stators with different teeth or irregular spacing between them. If they existed, they wouldn't pass QC at the factory. Here's a link to the NEMA manufacturing standards for stepper motors (http://bit.ly/2It4Yl0). If read it carefully (which I'll bet you won't), you will find that there is no tolerance specified for total steps, just incremental error. That's because it's a fixed parameter of the motor design, not related to possible errors in the manufacturing process. Incremental step tolerance is usually 5% or lower, but that's not for every step the motor takes, that's single-step error, which is independent of previous steps. If the motor makes three consecutive steps each with the maximum error, the final error is still 5%, not 15%. A motor that is spec'd to have 200 steps per rotation will have 200, not 201, or 199, or 210 (200 + 5%), it will be exactly 200. Your steps/mm are independent of incremental step angle error. Period.

2) Like stepper motors, lead screws have extremely specific and well-defined standards for their manufacturing. The average Joe can't set up a lathe in his garage, cut some trapezoidal threads into some rods and sell them as TR8's. The average consumers of these threaded rods aren't 3D printer owners, they're used in process automation and robotics, fields which demand not only precise products, but proof that you have deliberate and robust documentation of the entire process to back up your claims. Ask anybody who's ever gone through ISO certification, it's a massive pain in the ass that takes months. Speaking of which, the TR-series leadscrews that are so common in 3D printers fall under ISO2903:2016 standards, and require DIN103-e7 shaft tolerancing. Here's a link if you're still interested in arguing this point: (http://bit.ly/2IlJzuf). 7e shaft tolerancing is -25 to -40 *micrometers* for an 8mm shaft diameter. Oh, and TR leadscrews aren't Acme. They're trapezoidal.

Metric GT2 belt and pulleys are, again, bound to manufacturing standards, specifically ISO 17396:2017, here's a good handbook if you ever want to learn something about pulleys: (http://bit.ly/2InZQ1K). The GT2x6 belt on the X-axis of an Ender-3 is 720mm, and according to ISO standards the *total* allowable center-to-center distance error over that length is 0.3mm. Those standards apply to the pulleys, too, although you don't care about the actual diameter of the pulley because it has a fixed number of teeth/grooves, and if the diameter was off, the belt simply wouldn't fit and you'd have near-constant slippage and massive belt wear.

The bottom line here is that you will get the best performance out of your motion-related elements if you consider the physical specifications of your components. The manufacturing standards to which they are held far exceeds anything you can measure with a "hobbyist" digital caliper. BTW, check out Amazon's Neiko digital caliper, they're less than $20 and they have 10x the accuracy of a $10 set. To be honest, I don't know where you get off justifying "calibrating" your printer with a set of calipers that can acheive 0.2mm accuracy when used properly. I suspect that none of what I wrote will change your opinion whatsoever, but I wanted to make sure that anyone who is genuinely interested in properly configuring their printer isn't confused by your drivel.