Final answer:
The limiting factor for how deep to cut with an endmill is determined by the material's hardness and cutting parameters.
Step-by-step explanation:
The limiting factor for how deep to cut with an endmill in a particular material is typically the material's hardness and the specific cutting parameters used.
For example, if a material is very hard, it may be necessary to use a slower feed rate and lower cutting speed to avoid excessive tool wear and breakage.
Additionally, the rigidity of the machine and the endmill itself can also play a role in determining the maximum cutting depth.