Z axis jarring problems on RepRap Prusa Mendel i2.

After a few days of using my 3D printer, I found a problem, the Z axis would jar on the right hand side causing one side to be higher than the other and then both sides would jar as a result of the X axis not being level.


When this happened I notice that I could move the right hand side of the X carriage up and down and sometimes the nuts on the X carriage would be "left behind". this meant the X carriage would no longer be raised up and you could also move the X carriage up and down on the side that jarred because the nuts ( one on the top and one on the bottom of the plastic part that joins to the threaded rod ) would no longer be pressed tight against the plastic part.

I thought that this problem was because the X carriage wasn't level in the first place as I hadn't checked it. So I levelled the bed making sure the distance D on the diagram was the same on both sides ( see image below ). However when I checked it was level and put the nut back into place I kept on getting the same problem.

I then looked online to see if any one else had this problem, I found one post on the RepRap forums about the Z axis stepper motors vibrating and not turning and the solution was to reduce the speed of the two Z axis stepper motors. I tried this and it worked! I slowed mine down to about 50 mm/min in pronterface and the axis stopped jarring.

I also found other causes of jarring, jamming and vibrating Z axis, these are:

- over heated stepper motors
- damaged threaded rods
- something has got caught in the nut
- X carriage not straight

and my solution, slowing down of the stepper motors!

This problem was all to do with the force that the stepper motor needed to exert to turn the Z axis was to great and so it was missing steps, stopped rotating the axis. therefore anything to stop forces building up would help. things like cleaning and lubricating the smooth and threaded rods would help reduce friction etc...

Here is the video of the Z axis jarring:

Please correct me if anything I have said is wrong!, and please message me if you found this useful or have any other suggestions :)