<p>I'm trying to print a supporting base which will house the spindle for an electrostatic rotor. It's basically just a truncated cone with a hole down it's center to house the spindle.</p>

<p>For reasons that I cannot fathom, Ultimaker Cura keeps on adding an unrequested top/bottom layer (color-coded yellow in the screenshots) inside this hole, so instead of a single hollow cylinder of 10&nbsp;mm depth, the result is a hole only a few millimeters deep with another hollow cylinder behind it.</p>

<p>Here is the intended model, note the open space for the hole at the top.</p>

<p><a href="https://i.stack.imgur.com/tUdBC.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/tUdBC.png" alt="enter image description here"></a></p>

<p>Here is the inner view of the hole being printed as expected:</p>

<p><a href="https://i.stack.imgur.com/kXV5x.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/kXV5x.png" alt="enter image description here"></a></p>

<p>Finally, here is a layer view of the print a few millimeters from the final top layer with the unrequested top/bottom layer that covers the spindle hole:</p>

<p><a href="https://i.stack.imgur.com/Yd8mn.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Yd8mn.png" alt="enter image description here"></a></p>

<p>The STL file is on <a href="https://github.com/gearoid-murphy/3dprints/blob/master/spindle.stl" rel="nofollow noreferrer">Github</a> (with a built-in viewer).</p>

<p>Can anyone help me understand why this is happening?</p>

[{'answer_id': 10841, 'author': 'fred_dot_u', 'author_id': 854, 'author_profile': 'https://3dprinting.stackexchange.com/users/854', 'pm_score': 3, 'selected': True, 'text': "<p>It would appear that your model does not conform properly to STL standards. I base this conclusion on a couple of factors. When I loaded the model into Simplify3D slicer, it displayed fine, but when sliced, displayed nothing. Using the onboard repair feature, it presented the entire model as being composed of non-manifold surfaces.</p>\n\n<p>Meshmixer's Analysis/Inspector feature also highlighted the entire model as flawed.</p>\n\n<p>Another observation is that there is an extraordinary amount of facets/triangles/faces to this model. Nearly three-quarters of a million triangles for something that should be much simpler.</p>\n\n<p>The most recent version of Prusa Slicer 2.0 presents an error message indicating that no layers were detected. This is peculiar indeed.</p>\n\n<p>All of the above points to a problem with the source file or the software used to create it.</p>\n\n<p>Please consider to add to your post the program you used or the source of the model.</p>\n"}, {'answer_id': 16212, 'author': 'Pablo Quintana', 'author_id': 28106, 'author_profile': 'https://3dprinting.stackexchange.com/users/28106', 'pm_score': 2, 'selected': False, 'text': '<p>I had the same issue exporting from Sketchup to STL. I imported my STL to Tinkercad and then exported it again and it resolved my issue.</p>\n<p>Tinkercad is a free and online tool.</p>\n'}]
['https://3dprinting.stackexchange.com/questions/10839', 'https://3dprinting.stackexchange.com', 'https://3dprinting.stackexchange.com/users/17363/']