Assembly issues: 20:1 12mm worm Z drive

[ameyp]

List of issues I encountered during assembly:

1. The long bolts holding the motor should be m3x45 instead of m3x40. The distance between the top and bottom of the drive is 39mm, leaving just 1mm on a 40mm bolt.
2. Some Aliexpress spur have 7mm hubs instead of 6mm, making it necessary to use multiple 1mm shims instead of 3mm spacers in order to get full tooth engagement between the worm and the spur