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Sharp inside corners

You might need a rectangular hole (or any sharp corner shape) into which you will slide a rectangular male item (e.g. a power switch). If you draw a simple rectangle you might receive a warning that the corners will be rounded which could block insertion of the rectangular item. In this case consider creating a shape like this:



To create a mating shape (like above):
  1. Draw the shape of the male component.
  2. Select Line | Corner | Mate | Inside.
  3. Enter the desired radius – it is recommended to use the largest acceptable radius.
  4. Click OK.
  5. Increase the size of the female shape slightly for clearance and tolerance using Line | Contour | Outside.

Also see how to round and chamfer edges.

The above shape can also be created manualy:


  1. Draw a rectangle.
  2. Draw a circle of the desired corner diameter – say .25″. Typically you can use the Minimum Cutter Diameter value.
  3. Click the Repeat button three times. 
  4. Drag the circles so that their top snap points snap to each corner of the rectangle.
  5. Rotate each circle around the rectangle’s corner the appropriate multiple of 45 degrees.
  6. Select everything.
  7. Choose Line | Intersect.
  8. Delete the interior segments.
  9. Group the line segments.
  10. Set Z to Air Inside.

Why not sharp corners?

Sharp inside corners are problematic because most cutting processes use round tools. Round cutting tools can make sharp outside corners and sharp corners at the bottom of a pocket but not at the corners of the walls of a pocket. Imagine taking a block of ice and creating a square pocket (recess) with a round hot metal rod – you can’t get sharp corners at the walls of the pocket because the rod is round. For 2D processes (cutting sheets) tools are often very thin so you can get close to a sharp corner. For 3D processes tools of small diameter can be used but they usually cannot reach deeply as they will break. 


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