[OpenSCAD] STL triangles inside a cube

[cbernhardt]

I have an STL file of a car body that I would like to 3D print. The file is
just a representation of the surface of the car body with no thickness.
Because of the size I would need to print the model in several pieces. Is
there a program that would let me define a cube that would enclose a certain
area of the car body and output an STL file with the triangles intersecting
the cube sides having edges lying along the cutting edges of the cube’s
faces? I have tried using difference in OpenSCAD, but I guess OpenSCAD does
not like the STL file because it is not a solid.
See attached picture. The new STL file would have all of the triangles
inside the gray cube.
<Loading Image...>



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[fred_dot_u]

If the outside of the car body is one contiguous surface, (or even if it
isn't), you might be able to use Meshmixer to perform the task.

One feature of Meshmixer is Analysis/Inspector which will look for manifold
failures and attempt to correct them. I suggest using the Edit/Plane Cut
feature to chop your model in pieces, then use Inspector to correct errors
of the individual parts. Within the Plane Cut feature, the default option is
to close the sliced faces, providing an effectively solid part for 3D
printing.

When using Plane Cut, the program automatically sets the cutting plane at
the midpoint of the body. This can be advantageous, but it also gives you an
idea where your cuts will be relative to the entire model. Use
Analysis/Dimensions to see the overall size of the model, which then gives
you a better idea where to place your cuts.

Within the Plane Cut option, holding the mouse button on a transform arrow,
then pressing the up and down arrows will change the scale resolution from
the initial coarse spacing to even more coarse or much finer spacing,
allowing for 0.1 millimeter positioning.

You can keep or discard the "cut-off" pieces. I suggest that you use the
keep option and perform the desired cuts. Once cut, use the Edit/Separate
Shells to segment the sliced parts. This will present you with the object
browser and you can use the eyeball icon to vanish individual pieces.

Another feature inherent to Meshmixer is that you export the parts by
selecting each one in turn. The export defaults to only the selected part,
unless changed in the preferences. Having the entire model exported as a
whole is useful if different materials or colors are to be used in the
print.

Additionally, the position relative to the origin of each part exported
remains in the saved file. This will cause a drop to the bed when sliced, in
some slicers. It may be necessary to perform rotation on those parts to
ensure you have a flat part on the bed.



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[Frank van der Hulst]

FreeCAD also has a mesh analyser/repairer which finds different faults from
those that Meshmixer finds.

Post by fred_dot_u
If the outside of the car body is one contiguous surface, (or even if it
isn't), you might be able to use Meshmixer to perform the task.
One feature of Meshmixer is Analysis/Inspector which will look for manifold
failures and attempt to correct them. I suggest using the Edit/Plane Cut
feature to chop your model in pieces, then use Inspector to correct errors
of the individual parts. Within the Plane Cut feature, the default option is
to close the sliced faces, providing an effectively solid part for 3D
printing.
When using Plane Cut, the program automatically sets the cutting plane at
the midpoint of the body. This can be advantageous, but it also gives you an
idea where your cuts will be relative to the entire model. Use
Analysis/Dimensions to see the overall size of the model, which then gives
you a better idea where to place your cuts.
Within the Plane Cut option, holding the mouse button on a transform arrow,
then pressing the up and down arrows will change the scale resolution from
the initial coarse spacing to even more coarse or much finer spacing,
allowing for 0.1 millimeter positioning.
You can keep or discard the "cut-off" pieces. I suggest that you use the
keep option and perform the desired cuts. Once cut, use the Edit/Separate
Shells to segment the sliced parts. This will present you with the object
browser and you can use the eyeball icon to vanish individual pieces.
Another feature inherent to Meshmixer is that you export the parts by
selecting each one in turn. The export defaults to only the selected part,
unless changed in the preferences. Having the entire model exported as a
whole is useful if different materials or colors are to be used in the
print.
Additionally, the position relative to the origin of each part exported
remains in the saved file. This will cause a drop to the bed when sliced, in
some slicers. It may be necessary to perform rotation on those parts to
ensure you have a flat part on the bed.
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[cbernhardt]

Post by fred_dot_u
If the outside of the car body is one contiguous surface, (or even if it
isn't), you might be able to use Meshmixer to perform the task. .......

Thanks. I have used the Meshmixer Plan Cut feature. The project I have in
mind would require almost 20 "cuts", so I was hoping there was a less
complicated solution.
Charles




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