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Push a shape into another? (by Kevin)

I'm looking for some help on generating a trapezoidal shell. Basically, I'd like the final object to be shaped like a trapezoid, but hollowed out in the middle with a smaller trapezoid. I can't work out how to orient this, unfortunately. If I draw both shapes on the same plane, I can establish the correct dimensional relationships, but then when I extrude they share one face. I haven't been able to find a way to set an offset for the smaller object so that it will sit neatly inside the outer shape.

If I try to go at this from one of the other faces, I can't draw the trapezoid. From the bottom, I can sit the smaller shape inside and create my walls, but the shape looks like a rectangle from that vantage point. I don't want to cut out a rectangle because it'll make the wall too narrow at the top.

I think I can make it work by orienting at the bottom, drawing a construction line for the shell thickness and perpendicular to the top surface. Then, create a new workplane from a point on that line. But, then the drawing is all being done internally, since one side from the outer trapezoid sits on top of it. It looks like it'll work, but it's really tedious trying to draw behind another shape like this.

Is it possible to do what I'm looking for? In an ideal world, I'd just create a new shape and "push" it into the other and take the difference between them. I think being able to set an offset from that shared face might do it.
Sun Oct 11 2020, 13:52:57
(no subject) (by Kevin)
Following up to my previous question, I discovered the "stipple occluded lines" function and that makes drawing a shape inside another shape considerably easier. So, I've managed to draw the inner trapezoid. I'm still curious to see if there's a way to offset an extrusion.
Sun Oct 11 2020, 14:38:01
(no subject) (by Andrew)
The usual approach would be to draw and extrude the outer shape, and the draw and extrude the Inner shape as a difference. Alternatively, and easier for more complex shapes, is to use two or more files. Such as create the inner shape in one file, and then the outer shape in a second file, and in that file, link assemble the Inner shape as a difference. You could create the two shapes in their own files, and link assemble them in a third file. The multi-file approach is required if the Inner shape requires more than on extrusion.

Construction lines and/or reference points can be used to offset one drawing plane relative to another.
Sun Oct 11 2020, 15:13:28
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