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3D polylline/2D polyline extrusion?


Marvin7

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I'm trying to understand extrusion to 3D solids better.

This started when I drew a joined, closed 3dpolyline and found it wouldn't extrude (the shape titled 3D POLYLINES 4 sides joined, in the attached DWG), even though everything lies in the same plane (z=0). It gives the error "segment chord not perpendicular to normal". A chord is part of a circle, and there are no circles in the .dwg, so I don't understand the error. If you join only 2 or 0 sides, then at least 2D extrusion to a surface is allowed, but not if all 4 sides are joined, i.e. one 3D polyline.

 

If I draw regular polylines overtop the 3D polylines, then join and close them, it extrudes into a solid. This suggests that 3D polylines can't be extruded into a solid when regular polylines can, yet if I draw some scratch 3D polyline geometry that is joined and closed, these 3D polylines will join. It's as if I've found some secret shape that AutoCAD refuses to allow extrusion on. Any ideas?

3_D_polylines_won_t_extrude.jpg

3D polylines won't extrude.dwg

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The 3Dpolyline is not coplanar, set units precision to the maximum, and see

 

Henrique

Good thought, but I personally like having my unit precision set to 0.000, which is what it was already set to in this drawing. z=0.000 for all four corners (I re-checked).

Anyway, if all four corners weren't coplanar, the regular polyline extrusion wouldn't work either, but it does. It's just the 3D polyline extrusion of this exact shape that doesn't seem to want to work.

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Not coplanar, as hmsilva said. By having the precision at 0.000, you'll only see errors that are larger than half a thousandth. That doesn't mean the errors don't exist, you've just told AutoCAD you don't want to know about them.

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Not coplanar, as hmsilva said. By having the precision at 0.000, you'll only see errors that are larger than half a thousandth. That doesn't mean the errors don't exist, you've just told AutoCAD you don't want to know about them.

Hey, thanks, both of you. One corner was off by 0.00000001. That one was really bothering me. The reason I was convinced I had checked (and re-checked) accuracy sufficiently is because I'm used to imperial units like 1/16" hiding small differences. If need be, 0.000 is what I switch to to reveal small differences, and I was thinking if 0.000 doesn't reveal a difference, there's not going to be. Obviously, that wasn't true this time, though I still can't imagine how a 0.00000001 difference could have occurred. Is there any way to get AutoCAD to treat all points within 0.001 of each other as the same?

 

So to take it further...now if I move the one bad corner by -0.00000001 to correct it, the shape will at least extrude to a surface, but not a solid, even though the extrude mode is set to solid. Any more ideas? Presspull extrudes to a solid on the same shape, oddly enough.

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I just recently added Express Tools (Mechanical comes with it disabled so you have to manually load some .fas files to get it to work) and, yep, that works. Looks like AutoCAD knows when a point is off by as little as less than 0.00000001. In other words, the geometry still was not flat.

But I also went back and re-corrected the corner, this time using point filters instead of direct entry to move the corner down ~0.00000001 and afterward the geometry extruded to a solid with no troubles, which confirms it.

 

It would be nice if there was method to check whether geometry is planar that shows which location is the odd one if all but one are coplanar. Granted, that's probably a stretch. Nevertheless, thanks for the help, hmsilva. I'll know what to be careful of in the future.

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