How do I trim the edges of a complex shape in Inkscape?

Question

I have a complex (hand-drawn) shape from which I am creating a two-part cutter. The inner part of the cutter needs to be smaller than the outer part by a couple of millimeters on all edges for it to fit.

I can change the path around the object to white, and make it much thicker, and this appears to shrink the shape in the middle in the way I want. But it doesn't really; the white path is still there, which is a problem when I convert it to a 3D printing file.

What I'd like to do is something like making the path wider, then removing the path, leaving only the filled center area (now smaller). However, this is probably the wrong way to do this.

How do I make the complex shape a couple mm smaller on all edges? Note that simply shrinking it linearly won't work because it has concave sections; I basically need to "trim" a couple mm from all edges.

Answer 1

Try using the Offest path effect in Inkscape 1.0. It's located in the Path Effects.

In the Path Effects panel you can set a size in mm for the offset, then you can do Object > Object to Path to convert it into an ordinary path.

Example showing the Offset path effect applied to a shape