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

The most likely cause is the Z axis is slightly slanted relative to the bed surface. It could be that the bed is not level for some reason, or the Z axis is not perfectly vertical.

You could try loosening the Z motor brackets and sliding them right as far as the screws allow and re tightening them (while the axis is at the bottom). Then loosen the Z bar clamps and slide those right, with the axis at the top. The axis should then be perfectly vertical. If you still have the problem move the bar clamps left as far as the screws allow. That should slant the axis and lower the idler end a little.

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[www.hydraraptor.blogspot.com]

Thanks Chris,
I loosened the motors and clamps as suggested and moved the motors right with the X-axis at the bottom and the top clamps left with the axis at the top. This had taken out most of the play and a test print 150x150x0.2 thk has printed at the correct thickness both sides. I do not think that any slant of the Z-bars will be noticable as most of my prints are not very tall.

Richard