Boolean difference display issue

I believe that this is only a display issue, but it still worries me, Differencing my bas cyl like shape that lists as a closed polysurface seems to delete the lower cap, yet it still lists as a closed polysurface.
BSP-2B-PC IM 630-lid-lugs.3dm (2.9 MB)

“What” shows: “Geometry:
Valid polysurface.
closed solid polysurface with 49 surfaces…”

How did you create these polysurfaces?

Part of the problem could be a short segment on the boundary of your base surface.

outline->planarsrf=>delete outline curve->exrude surf->verify closedpolysurface.
Update, saved as stl shows it is closed

_ExtrudeSrfTapered ???

A straight extrusion works fine…

Injection molding requires a taper in order to remove from mold. :frowning:

Yes but you cannot expect a short segment to extrude correctly…

Why not, it’s just math? It worked just fine on previous models.

What taper angle are you using?

3 degrees every time.

Ok. I see a short segment with a length of 0.008 inches.

To demonstrate the effect, I extruded a square surface with a side lenght of 0.008" with 3° taper.

0.004 / tan(3°) = 0.076… and then there’s tolerance

I was able to extrude square with the side length of 0.008 inches with 3° taper to a height of 0.0597, anything higher failed.

You will have to clean up the surface you extruded or add fillets after the extrusion.

Pure math.

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The taper has resulted in one or more self-intersecting surfaces which will screw up your boolean:


EDIT: The odd semi-transparent display is a clue to the presence of a self-intersection.


thanks guys

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