I have had my Mendel90 for just over a year now and it has been trouble free.
Yesterday I re-taped the mirror tile and the next print had a squished first layer.
I decided to check the bed for level and the Z home position. I installed my dial gauge and levelled the z-axis to the back corners of the bed. I then noticed that there was play between the left hand Z axis nut and the top of the nut trap. I could press the idler down about 0.1mm and feel the idler moving with a 'clunk' relative to the threaded rod. I loosened the X-bar clamps and the left hand idler sat down correctly. However despite tightening the X-bar clamps in various ways the play still occurs. I have also re-taped the Z-axis nut in case this was the problem. I have checked for any broken parts and none are apparent. I have not noticed this play before and wondered whether anybody else had experienced it. The printer has not been moved for many months.
One thought on how to cure it was to insert another washer under the left back bed support so that the left hand idler would need to be higher however this would only cure the symtoms and not the actual problem.
Richard