In some cases, the actual material dimensions are slightly larger than those defined in the stock model. This is due to inaccuracy at the saw or additional material remaining.
In this case the first pass of the Global Rough/Rerough toolpath can remove to much material and possibly damage the tool.
This is where the Initial Lateral Step parameter is used. Instead of the first pass being performed at the programmed stepover value (minus the stock allowance), the first pass will be made at the value of the Initial Lateral Stepover (minus the stock allowance).
This will allow the user to compensate for the additional material by programming a smaller first pass stepover.
