Denford Software & Machines

I have students wanting to cut out components on our vertical router. they are importing the DXFs selecting each group of contours that make up the component and hitting 'join' when in the CAM wizard the pop up says "contains open contours" and the machining plan cuts the thing to pieces.

Any ideas?

You can see where the join has failed.
In the CAM wizard you will get line(s) appearing across the shape. It's at the start and end of those lines that the shape has not joined properly.
Usually it struggles to join when there are lines or polylines directly on top of each other.
You can select the joined polylines and move them slightly.
Then explode them all to single lines and try a re-join.