I recently noticed the X axis wobbling in my newest sand table mechanism when the magnet carriage moved back and forth along the X axis with Y fixed. That got me thinking that maybe something similar could be happening in UMMD.
I set up a digital gauge and wrote a simple gcode file to test the machine. The gauge was mounted on the Y axis guide rails and the extruder carriage was made to move across the bed along the X axis, stopping every 5 mm to make a measurement.
![gauge%2Bzero.jpg]( "gauge%2Bzero.jpg")
I found some interesting behavior- the movement from one end of the X axis to the other displayed a maximum shift of about 70 um, with a lot of waviness along the way. The wave period is 40 mm which matches the distance traveled by the carriage with one full rotation of the drive pulleys. It looks like the waviness can be attributed to the drive pulleys being either out of round or having poorly drilled center holes for the motor shafts.
[attachment 117200 Clipboard01.jpg]
I don't yet know if the 70 um error or the waviness has any effect on print quality- as someone pointed out, 70 um is about the diameter of a human hair. The error seems to be consistent with repeated measurements falling within the precision spec of my gauge. That means a vertical wall printed parallel to the X axis should have the layers stacking precisely on top of each other, waves and all, so the effects on print quality should be limited to visibility of the 40 mm periodic waves and not to any Z axis artifacts. I think.
I wrote a blog post on the subject [drmrehorst.blogspot.com]
I set up a digital gauge and wrote a simple gcode file to test the machine. The gauge was mounted on the Y axis guide rails and the extruder carriage was made to move across the bed along the X axis, stopping every 5 mm to make a measurement.
I found some interesting behavior- the movement from one end of the X axis to the other displayed a maximum shift of about 70 um, with a lot of waviness along the way. The wave period is 40 mm which matches the distance traveled by the carriage with one full rotation of the drive pulleys. It looks like the waviness can be attributed to the drive pulleys being either out of round or having poorly drilled center holes for the motor shafts.
[attachment 117200 Clipboard01.jpg]
I don't yet know if the 70 um error or the waviness has any effect on print quality- as someone pointed out, 70 um is about the diameter of a human hair. The error seems to be consistent with repeated measurements falling within the precision spec of my gauge. That means a vertical wall printed parallel to the X axis should have the layers stacking precisely on top of each other, waves and all, so the effects on print quality should be limited to visibility of the 40 mm periodic waves and not to any Z axis artifacts. I think.
I wrote a blog post on the subject [drmrehorst.blogspot.com]