How do I “subtract” sketches in CAD?

Question

I am using 123D Design to build a model for 3D printing. What I want to build is a large 2D rectangle with several smaller rectangles inside. Then, I want to extrude the larger rectangle, but leave the smaller ones as holes.

I thought that I could subtract the smaller rectangles from the larger one and then extrude the remainder. However, when I use the subtract tool, I cannot select sketches - just solids.

Any ideas on how to do this? I would very much like to know how to do it 2D first, and then extrude the remainder. However, if I must transform this to 3D first, I'll be willing to learn that instead. Much appreciated!

Answer 1

Sketches aren't usually part of the actual model until you use them to define a solid feature. In general when you extrude a sketch with closed loops inside it the inner loops will be excluded from the extrusion or, depending on the software, you will have the option which closed loops are selected as part of the extrusion dialogue. So it is quite likely that what you want will happen by default, depending on how your particular software package deals with selections.

Some software packages will allow you to define 2-dimensional surfaces but many don't as they can make models difficult to manage and you can only work with points, lines and volumes (solids). In many cases there is a distinct separation in the workflow between sketches used to define solid features and the features themselves.