prusajr/PrusaMendel — Issue #38: x-end-motor/idler centres different from Z-motor mount - URGENT!
Author: droftarts
Created: 2011-11-30 11:39:10+00:00
State: open

I have carefully measured this in Netfabb, and noticed it when I printed out the felt branch. Distance of motor centre (or Z-leadscrew centre) to Z-rod centre on Z-motor-mount = 30mm, same distance on X-end-motor and X-end-idler = 29mm. Which means the Z-axis motor coupler will ALWAYS run eccentrically.

And this is made even worse as NEMA17 motors are 42.3mm square on the end http://www.zappautomation.co.uk/pdf/steppermotors/SY42STH47-1684A.pdf , so 21.15mm from centre to edge, while the distance from the centre of the motor shaft to the 'wall' between the motor and the Z-rod is 20.8mm, so motor is pushed EVEN FURTHER away from the Z-rod. I guess this is why triffid in Issue 20 https://github.com/prusajr/PrusaMendel/pull/20 moved the motor centre, but in doing so causes the X-leadscrew to run EVEN MORE eccentrically as the motor centre moves to 31mm from Z-rod centre.

I suggest removing 1mm of the wall from between the motor and Z-rod, to allow NEMA17 motors to fit and maintain the 30mm spacing. The X-end-motor and X-end-idler need to be amended to have the 30mm spacing between Z-leadscrew centre and Z-rod centre, which is currently 29mm. I think this may have been an issue for a long time!