Box Sides

[robboz4]

I was trying to make a small box with interlinked corners. However, I'm not having much success working out what happens when the unit scales the image. It seems to not keep them in the same ratio. I think this is explained in the manual. But does anyone have a suggestion on how I might do this? I have uploaded the file I was using and a second one where I thought I would carve out the corners, then use the rip & cut functions to remove the "sides".


Thanks!