Spot drill tells the system whether or not to spot drill (or center drill) a hole before drilling. This operation has some wide ranging effects, however, especially when used with the Attempt Chamfer w/ Spot and tool optimization. Of those three settings, tool optimization has the highest priority and it’s decisions override settings with a lower priority.
For example, a spot drill operation could be performed with either a spotdrill or a centerdrill. Spotdrills with a tip angle of 90_ can also perform a chamfering operation. You specify a specific tool to cut the hole’s chamfer and also turn on Attempt Chamfer /w Spot and tool optimization. If there is an appropriate spotdrill in the toolcrib FeatureMILL will optimize things and use this tool in spite of your lower priority override. Even though you selected a specific tool, your other settings conflicted with and superseded your choice.
This is the advantage of FeatureMILL’s optimization and simulation functions. As you work through the optimization settings, and see where you can optimize automatically and where you can’t, you can find ways to group your parts for faster production, but still use specific tools for specific effects when needed.