For me, I've never done well w/ traditional 3D CAD (need to find time to try Moment of Inspiration 3D), and I've been working on wood joinery where a test joint which was 1" x 2" x 1" took some 20 minutes to do CAM, and created a ~120MB file --- programming the tool movement directly seems a better approach, so I've been working on:

https://github.com/WillAdams/gcodepreview