Lulzbot Mini 2 not printing z dimension accurately

I have a Lulzbot Mini 2 and I am trying to print small samples of PLA 10x10x2 mm. However, when I try to print these samples, the thickness is always about half of what is desired. I have tried printing taller things such as a 20x20x20 mm cube and there is still the same problem. The x and y dimensions are pretty accurate, but the z direction is shorter by a significant amount.

In addition, I have noticed that printing across the bed in the x and y directions also have a difference in thickness (z direction). For example, if I print a long, thin rectangle across the x axis, one side has a different thickness than the other side. Could this problem be caused by the table being slightly not leveled? Could it be something else?

Before every print, I always level the x axis and I did reset it to all defaults and that didn’t seem to work. I also took out the corner washers completely and then re-screwed them to make sure that they were equally tightened/level. I have a flex bed instead of the glass bed. I’m not sure if that makes a difference.

I would greatly appreciate any advice on how to fix this problem. Thanks!

From the simplest on:

How are you leveling the X axis? There’s an option to auto-z align in the motion menu that pushes the Z axis down completely that helps. If it goes to the top and keeps pushing, the right side ends up higher than the left. The software should theoretically compensate, but it doesn’t completely. If your mini has been “leveling” off the top, it’s probably not level.

Seriously check for absolute cleanliness of the nozzle. Stray strings off of the cleaning pad or a spec of plastic on the nozzle may be the cause of an improper bed leveling with the washers.

It might be as simple as your z steps/mm is incorrect. You can use measurements on your 20mm cube to adjust with the simple calculator here: 3D Printer Calibration - LayerFused - but this doesn’t address the slanted prints.

The Z motors share a driver, but pass through the Z brake board. If one of the stepper motors is failing (fairly unlikely with how little load they get) it’s going to be holding back the other side, and causing shorter Z heights and differing thickness. The problem could also be a failing Z brake board. They’re around $50 from lulzbot. I cannot say for certain that you can just swap the Z stepper connections around and see if the problem mirrors to the other side, due to how the Z brake board works. I would not be surprised if the motors flipped up/down directions if you tried that, so swapping in alternate motors to test the board is probably easiest, and steppers are cheaper than the Z brake board.

I have the same problem Estudent. It frustrated me for quite some time and I tried everything to fix it. In the end, I finally accepted it as an intrinsic design limitation (flaw maybe) of the belt driven Z axis, at least the way it is implemented on the Mini 2. Not a satisfying answer, but I reached my limits trying to solve the problem.

I now deal with it by printing with a raft. It works for me, since I am printing mostly small parts with Taulman Bridge Nylon. In this case, it also helps with bed adhesion and prevents warp so I’ve learned to accept it.

If you run a few prints with the raft, you will see that it randomly varies quite a bit, from a nice fluffy pancake to a very thin crepe., but the part turns out fine with no loss of height.

I appreciate your post. I tried several times to compose one myself, but I couldn’t find the words to describe it the way you have. Hopefully someone will have found a better solution.

Thank you or the suggestions, Wrathernaut. I guess I didn’t try everything.