Conceptualizing 3D Toolpaths

There is a story about a man admiring an artist cutting the sculpture of a bear from a log. Impressed and amazed by the artist's ability, the man inquired how he was able to create such realism. The artist replied, "It's easy, I just cut away anything that does not look like a bear!"

3D machining is a similar mindset. You begin with a block of material and cut away anything that does not belong. Begin by getting rid of excess material as quickly and efficiently as possible. Try to leave a constant thickness of material for finish operations. Finish as much of the part as possible using the largest tools possible. Then finish machine finer features and details using Parallel or Scallop paths contained by 2D profiles, or REST and Pencil tool paths.

3D machining can be very challenging, but in many cases it is easier than many 2D parts. Some 2D parts involve scores of machining operations that require considerable forethought and work. Most 3D parts require fewer operations and these are largely automated by CAD/CAM software functions.

The key to success is planning ahead and preparing the model before creating tool paths. In the case of 3D machining, perhaps 50-80% of the time programming is actually CAD-related, getting the model ready for tool paths: creating runoff surfaces, suppressing features, creating check surfaces, and the like.

Don't begin making tool paths until you have a credible plan. If your planning is thorough and the CAD model is simplified so only those features to be machined are displayed, creating tool paths is far easier and outcomes better. To aid planning, use the forms in Appx C - CNC Process Planning Forms.