Thanks @gr5 for working with me on this issue! I took the z axis rod off and made sure to clean it well. I did notice some dirt on it. When I was done it was very clean. I sprayed it with silicon. I reassembled the machine and added a weight to the x gantry. The heaviest weight that I could find that I could put on the machine was a 100g weight. I also noticed that the x gantry was hard to move up. I noticed the rod tension screws were super lose so I tightened them not too much and the x gantry moved up much smoother.
The results didnt appear to be much better.
Was the 100g weight not enough?
Also, I failed to mention that anything I print out always comes out .2 to .3 mm shorter than it should. I really don't know why this happens. I suspected a very squished first few layers. But after setting my z offset higher (-2.4 down to -2.3) I still got the same results .2 to .3 mm too short.
Thanks!
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gr5 2,243
A bend in the z rod or wobbling will create a smoother, harder to see, wave like pattern. Your issue is different.
What happens in your case is that the bed isn't always moving a consistent amount - it gets stuck a bit and so it over extrudes a layer (not enough space for the plastic extruded) and then on a later layer (sometimes the next) the bed moves the full amount of all previous desired moves that were incomplete and you get an underextruded layer.
One thing to try is to add a brick or some heavy object so that when the Z screw rotates the bed is more likely to come all the way down and rest on the threads once again (or if it's your print head that goes up then a weight can help wilt that also).
Usually the fix is to clean the Z rod. If you want to do an extra good job, then remove it completely (typically the stepper is attached which is fine) and then clean it with wd-40 and tooth brush and dry completely with rag or paper towels.
I'm not sure about lubrication. Ultimaker recommends a particular grease (don't know the brand or anything) and they recommend oil for the straight rods (no oil on threaded rods). I don't understand the logic of these choices at all. If you have a fancier, more expensive Z nut (like $3 instead of $0.50) then it should have ball bearings inside and you probably don't want any grease or any oil (as this collects dust in with the ball bearings).
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