# arc extrusion question

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Hi all-

Excuse me if this is a really naive question, but I havent figured out a way to extude an arc in 3d without getting it to turn into a large piece of pie shape. To explain-

The shape I am building is essentially a long thin box, but one half of it has an arc to it. So, there is a gentle rising arc (vertex is below) then straight across. That linear shape is the same on the bottom, and the endpoints are capped off with a straight line.

Now, this all draws out just fine. But if I got to do a 3d extrusion, instead of extruding just the arcs, it also extrudes lines not previously there, which connect the ends of the arc to the radius. So now my thin shape with a slight curve on one side has a large triangular shape hanging underneath it.

I am new to VW (being an autocad transferee) so I am positive I must be doing something silly. But I just cant figure out what. Shouldnt the arc just be... the arc itself? And not include geometry related only to its creation? (since I niether drew nor can even see the new lines it pops into the extrusion.)

TIA everyone, really.

BTW I am on a PC version 9.5.2

And looking to get up to ver11 soon as I can swing it...

Eric

Eric,

Did you use the COMPOSE function to join the arc and line segments together before extrusion?

If you are not familiar with COMPOSE, it requires the endpoints of entities to touch in order to join them together.

Chris

Firstly, one should use extrusions only when walls won't work. (I assume the arc is in plan.)

Secondly, zero-thickness objects seldom make sense, except in pure visualisations.

Finally, the behaviour is a 'feature' so to speak. An arc with a fill becomes a slice of pie and so does an extrusion created with a no-fill arc and then filled.

Solutions:

1. Use walls.

2. Create a polyline with a thickness:

- copy the arc to clipboard

- paste in place

- send to back

- select both arcs and say 'Clip surface' (the larger arc becomes a polyline)

- delete the smaller arc

3. Instead of fill, use texture.

4. Convert the extruded arc into a mesh.

quote:

Shouldnt the arc just be... the arc itself? And not include geometry related only to its creation?

Not in VW. For extrusions, sweeps, roofs and floors, the original 2D geometry is kept 'inside' the resulting 3D object. The benefit from user's point of view is that the shape can be edited by saying 'Edit group.'

The above applies also to 3D solids: you can enter a solid and change its components & their relationships.

You will in future learn to appreciate this.

Hey all-

Maybe I didnt describe the geo well enough. It does have thickness. I did compose object beforehand, however, Petri seems to have answered my question.

Autocad user- I usually dont use the wall tools, but rather line draw the outer geometry and offset internally. Guess I better learn the wall tool!

Thanks for the detailed replies. Helps a ton.

Eric

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