Millbox will highlight the undercuts from a 3-axis milling analysis that could potentially create incomplete feature definitions in the mill.
Highlight undercuts is useful primarily in placing sprues, to indicate an area that may have residual material remaining that could impact your design or increase post-milling finishing times.
Undercut highlighting will indicate where residual material will remain if it's a 3-axis mill. A method to visualize how Millbox is highlighting these areas is that it is showing where the "shadows" exist when looking at the unit as if the light source was shining from the top (0°) and bottom (180°) views.
If you are setting up for a 4/5 axis mill, this highlight is useful if the strategy operation is using a fixed axis from the top and bottom views of the disc also. The milling simulation will confirm if these materials remain, but this feature will help you reduce your overall setup time.
Again, this is just a visualization that acts as a guide to help optimize your adjustments.
Use this tool AS A VISUAL GUIDE to help interpret where residual material may remain after milling, but not as a visualization of final results. Milling strategies will help eliminate these undercuts by utilizing undercut milling operations that will adjust the tool angle, or alter the View Automatic Tool Angle adjustments for cavities for 4/5 axis mills.
Areas where it is typically useful to try to minimize the undercut highlight on a unit
- Exterior/Facial/Lingual areas of a unit.
Unless the Undercut Operation is selected, exterior area finishing is typically done from fixed top (0°) and bottom (180°) axis milling.
- Areas that have slopes relative to the top and bottom greater than 15 degrees.
Areas where you can typically ignore highlights
- Cavities with margin curves (purple lines) in 4/5 axis mill.
The tool will adjust its angle to eliminate the undercuts, and most modern CAD packages eliminate these undercuts.
- Small singular triangular dots.
These may be detected as areas of undercuts but are small enough typically that they do not indicate anything. See above image.