Just found this problem using deburr on a vertically oriented cylindrical surface. May be relevant re. using deburr as a base for vertical surfaces:
The deburr tool seems to "work" for a rectangular, vertical face. However, I'm not sure what this means. I suspect it will cause a tool crash in this example with a countersink tool. See cylindrical-deburr file.
[Edit] confirmed, even with a straight tool the result on a vertical face is clearly wrong and will cause a tool crash. It is creating a path on the face as though it was perpendicular to the tool spindle even though the plane is parallel to the spindle. Ouch!.
OS: Fedora 31 (Thirty One) (LXDE/LXDE)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.18754 (Git)
Build type: Release
Python version: 3.7.5
Qt version: 5.12.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/United Kingdom (en_GB)