When you apply the Costing tool to a part that is machined from a block or cylinder stock type, the software calculates the difference between the stock material and the actual part, excluding machined features such as holes and pocket features. This difference creates volume features, which contribute to the cost of the part as a result of the required milling operations.
Volume features account for the cost of tooling a part from a block or cylinder. The cost of the machined part includes the following:
- The cost of the stock body
- The cost of tooling a volume of material from the stock body
The volume of material removed from the stock body to produce the part defines the volume features.
The Costing tool computes the contribution of the volume features to the total cost of machining the part.
After estimating the cost, the Volume 
features appear in the CostingManager in the Mill Operations 
folder. You can change the tool used to create a volume feature to adjust the cost. You can right-click a Volume feature and change the tool to modify the cost calculation. You might also have a volume feature appear in the No Cost Assigned folder.