<p>I have a weird problem with my old 3D printer, it is a Prusa/Mendel type.
When I print a 20&nbsp;mm cube, X and Y are correct, Z is resulting 16 to 17&nbsp;mm.
I have checked the correctness of the movement on Z using the manual controls and there are no issues.</p>

<p>I played a bit with the layer thickness, I have a 0.4&nbsp;mm nozzle, setting the layer height to 0.12&nbsp;mm (normally is on 0.16&nbsp;mm) but no changes in the result.
I am printing PLA on a cold bed at 180&nbsp;&deg;C without any other particular defect.</p>

<p>I would appreciate some direction on how to solve such problem.</p>

[{'answer_id': 2828, 'author': 'Tom van der Zanden', 'author_id': 26, 'author_profile': 'https://3dprinting.stackexchange.com/users/26', 'pm_score': 2, 'selected': False, 'text': '<p>You should check that the steps per mm for your Z-axis are set correctly. This depends on the pitch of the leadscrews/threaded rods driving the axis and parameters of your steppers (microstepping and raw steps/revolution). <a href="http://prusaprinters.org/calculator/" rel="nofollow noreferrer">This Calculator</a>.</p>\n\n<p>Make sure that your layer height is a multiple of a full step of the Z-stepper. The Z-stepper may be disabled intermittently, and when re-enabled it may "snap" to the nearest full step position. If your layer height requires microstepping, you may notice it getting rounded down or up due to this.</p>\n\n<p>For instance, if a full step were 0.08&nbsp;mm, then 0.16&nbsp;mm layers would require 2 full steps, printing fine. 0.12&nbsp;mm layers would require 1 full step and a half microstep. Due to rounding, some layers might be reduced to 0.08&nbsp;mm instead. This might account for the height discrepancy you\'re seeing (though 0.08&nbsp;mm is quite a high, unrealistic amount for a full-step).</p>\n'}, {'answer_id': 2829, 'author': 'Smitje', 'author_id': 4406, 'author_profile': 'https://3dprinting.stackexchange.com/users/4406', 'pm_score': 2, 'selected': False, 'text': '<p>You could check that the stepper driver IC for the z direction is not getting too hot while printing. If this is the case it may be that the current adjustment of the stepper driver is set incorrect causing it to skip steps. however you would expect the same behaviour in manual operation.</p>\n'}, {'answer_id': 2830, 'author': 'FeliceM', 'author_id': 4388, 'author_profile': 'https://3dprinting.stackexchange.com/users/4388', 'pm_score': 2, 'selected': False, 'text': '<p>Thanks to your advices I pointed my effort on the root of the possible cause on the Z axis.\nI swapped the Polou driver between x and z and clearly noted that now the problem is on x. I had to conclude that the problem is with the Polou driver which randomly looses steps.\nWhat is surprising me is that on the Z axis I have two motor type Nema 14 which should work at 0,75A therefore 1,5 A total. The Polou driver, old type, is rated at 1A. So it is not a surprise, now that I have learned about this configuration, that the z driver is giving troubles. The problem was there since the beginning and with the ageing of the components it revealed itself.\nI will replace the actual Polou drivers with the new type rated at 2 A and restart from there.\nThanks for the advices.</p>\n'}, {'answer_id': 10499, 'author': 'Sean Houlihane', 'author_id': 4927, 'author_profile': 'https://3dprinting.stackexchange.com/users/4927', 'pm_score': 0, 'selected': False, 'text': '<p>A suitable test part for this problem, to check if the bad scaling is linear or the result of missing steps (as was identified in this case) would be a ramp, or sequence of steps. You can check the linearity using a straight edge, and would be able to perform repeated tests to identify of there was a specific Z location where steps were more likely to be lost (for example due to some tightness in the motion system).</p>\n'}]
['https://3dprinting.stackexchange.com/questions/2826', 'https://3dprinting.stackexchange.com', 'https://3dprinting.stackexchange.com/users/4388/']