Finishing passes?

[mhotchin (Michael Hotchin)]

The problem you are seeing is almost certainly that the bit you are using is a so-called ‘fishtail’ bit:

Problems with 'Fishtail' endmills

Not all endmills create a flat bottom when plunged, for example the Carbide #251. In general, you can assume an endmill is creating a flat bottom *only once it has travelled at least 1/2 its own width". Edit: As Tod says below, the bit needs to move its own width. My current project is pocketing around letters, so the toolpaths are not regular shapes. In several places the toolpath is just a plunge with little to no travel, and in those areas the bottom is raised in the center because the #2…