What are the "magic numbers" people refer to regarding print resolution on the Monoprice Select Mini?
The "magic numbers" are optimal values that work particularly well for the layer height. Michael O'Brien derived these numbers by reverse engineering the mechanics of the Z-axis stepper motor.
Using these values as your layer height will generally improve your print quality over using round layer heights such as 0.15, 0.2, or 0.25 by eliminating quantization errors.
To see an example of this, print a copy of 3DBenchy at 0.15 and 0.175. On the 0.15, you will see some wavy patterns on the curved bow portion compared to the 0.175. This is the result of inexact rounding.
Layer Height (mm) 0.04375 (results may vary)* 0.0875 0.13125 0.175 0.21875 0.2625 0.30625
Though this approach is logical on paper, in the real world it doesnt work as well. Even if you do choose a magic number for the layer height, you cant gurentee that your print head, once homed at the beginning of a print, is using a full step of the motor. Its more common to be on a half step than a full step with a motor
This is an issue with homing. It is not synced to the stepper motor so it may occur on something other than a full or half or even quarter step. That said, it always does this so moving up from there, the first little bit may be off but I would expect once the motor runs freely, the error will go away. Also keep in mind with microstepping, you can have 1/16 or 1/32 steps as well. Using the magic number ensures the new position you request is within the limits of the stepper/controller to reach. Its like rounding numbers. if you don't, as you increment, the numbers will always be consistant. If you round, the numbers will dither around. At least thats my $45 (inflation) and stickin to it. Good luck everyone and have fun.