Stock engagement avoids the tool damage that occurs when machining excess stock and improves surface finish. It also enables you to use higher feed rates as excessive tool engagement is eliminated. Machining times are improved as this avoids air cutting by removing toolpath segments which machine little, or no material. This uses a stock model and is useful when semi-finishing.
This page contains the following:
Depth of cut — Select to enable you to specify a maximum allowable depth of cut into the stock material.
— Enter the maximum allowable depth of cut into the stock material. Clicking the Stock depth of cut 
button changes the Stock depth of cut box to Stock radial depth of cut 
and the Stock axial depth of cut 
box appears. Now you can specify separate Stock radial and Stock axial depth of cut values 
.
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Stock depth of cut — Specifies the depth of cut in all directions.
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Stock radial depth of cut — Specifies a radial depth of cut.
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Stock axial depth of cut — Specifies an axial depth of cut.
Machine stock only — Select to machine only the rest material. Segments of the toolpath which cut the rest material are kept. Segments of the toolpath which do not cut the rest material are removed.
Detect material thicker than — Enter a threshold value. PowerMill ignores rest material that is thinner than the specified threshold. This helps to avoid thin regions being machined, where the benefit of a second cut is negligible. These thin regions can be caused by cusps from the previous toolpath.
Minimum length removed — Enter a threshold value. PowerMill removes segments of the toolpath which do not cut the rest material and are longer than the specified threshold. Short segments which do not cut the rest material are not removed. This avoids the generation of fragmented toolpaths and associated air moves which would join these segments.
Stock model — Select the stock model used to determine the Depth of cut. If no stock model is selected, then stock model engagement is not considered.
Stock model state — Select the stock model state used to determine the Machine stock only options. If no stock model is selected, then stock model engagement is not considered.
For more information see Avoiding machining into unmachined stock and Machining stock only.