Stock: Stock is the raw material a machined part is cut from, such as a block, plate, bar or tube, sized a little larger than the finished part.
A machinist starts from standard sizes: plate in set thicknesses, bar in set diameters, cut to length. The stock has to include an allowance for facing, for holding the part, and for cleaning up every machined face. Because stock comes in the sizes a supplier sells, a part 49 mm thick may be cut from 50 mm plate, while one 51 mm thick may need the next size up.
What it means for the price
The material cost of a machined part is the cost of its stock, not the weight of the finished part. Everything between the stock and the part then has to be cut away, which costs time at the material removal rate. A part that is mostly pockets carved out of a solid block is expensive on both counts, and the buyer rarely sees why from the finished shape. How the stock is held also affects the allowance; see workholding.
Example: an aluminium part with a 100 × 60 × 20 mm envelope cut from 110 × 70 × 25 mm stock uses 192.5 cm³ of material for a 120 cm³ envelope, before any pockets are counted. The figures are an example.
Common confusions
In a shop, “stock” also means inventory on the shelf. In a quote it means the blank for the part. Read what drives CNC machining cost.
Go deeper: What drives CNC machining cost, and how estimators work it out