One can import an OBJ file into free program Meshmixer, then export it to STL format. There are other programs that are free and paid (such as Fusion 360) that will perform similar tasks.
As noted by user agarza, Prusa Slicer will import an OBJ and will also export to STL format. PrusaSlicer is also free.
support blocker button
drop anywhere on bed, then resize and move like any model, make sure to turn off uniform scaling
with support blocker selected
click that button
modify settings for overlaps
type infill in the ...
Basically all slicers work very similarly, it is a matter of preference, being accustomed, or wanting to use a certain (set of) features. Their job is to prepare the object to be sliced in layers to be executed by the printer you use. For every slicer to work properly, you need to configure the printer settings correctly.
Basically, all slicers have the ...
There are several problems at work here:
Internal Geometry & unjoined parts
Generally inverted surfaces: every surface is inside out!
Step 1: add missing surfaces.
Select the vertices around the hole that has no bottom surface and then pres F to create a surface. Use several steps, making roughly triangle surfaces. For ...
Okay, so like suggested I put it into 3D Builder (A free Windows 3D modeling program). I imported it as an stl, then exported it as an stl and imported that stl into Cura. And lo and behold all problems were gone! If you are having a similar issue give that a try! The 3D Builder program and similar ones are designed to export for the sole purpose of 3D ...
Rhino gives the following output for MeshRepair
Mesh has 3 degenerate faces. (a face that's actually a line or a point)
Mesh has 42 non manifold edges. (a line where 3 or more faces meet, possibly caused by degenerate faces)
Mesh has 6 duplicate faces. (faces that share the same coordinates)
Mesh has 148 naked edges (edges that have only one face)
All of ...
It's common for modeling software to flip normals, causing what you describe. You said,
I only care about the externally facing faces.
But are you sure they are truly externally facing? Turn on normals in Blender and ensure that all the arrows/pointers are external.
Another problem that can generate the results you're seeing are self-intersecting surfaces, ...