Here is a little FYI:

For IGES import and Version 18 or 19 BobCAD systems. The best format I have found is the "DelCAM" format. It comes in clean and all geometry is typically where it should be and in the proper scale.

For STEP import, use AP214CC2. Again, it is the cleanest format I have encountered. Some of you may not be able to control your IGES export, but you should all be able to control the STEP output.

For DXF import, this has already been sited but is worth repeating. Explode the file, you know that little fire-cracker icon in AutoCAD, then export as an R12. Also remember to close the file in AuotCAD before opening it in BobCAD. If you fail the last step the tug-o-war game you started will result in BobCAD failing to initialize properly.

Regards