aPriori supports the concept of a machining stock allowance when determining the initial stock size required to machine a given part. A stock allowance typically is a small amount of extra material added to the finished part dimensions to accommodate any machining (material removal) needed to meet material quality, tolerance or surface finish requirements. A non-zero stock allowance is necessary to drive rough- and finish- machining of the part. A zero-value stock allowance means that the “as-supplied” stock surfaces are sufficient for the finished part, with no additional machining required to achieve desired quality, tolerances or surface finish requirements.

aPriori computes the ideal stock size required for a part based on the following:

In general, by default in starting point VPEs, aPriori selects actual stock with the smallest standard thickness greater than or equal to the ideal thickness (and only selects virtual stock if there is no such actual stock). The setup option Stock Unit System (see Material Stock Options) determines whether aPriori uses metric standard stock heights or US standard stock heights.

You can override the default behavior and direct aPriori to select virtual stock if there is no actual stock with ideal thickness—see the process setup option Snap Up to a Standard Stock Height in Material Stock Options. VPE administrators can change a VPE’s default stock-selection behavior with the cost model variable snapStockSize (which is true in aPriori starting point VPEs). See Material Stock Options for more information.

For plate stock, if Roughing Technique is set to Plate Cutting with Dropoff (see Stock Machining Node Process Setup Option), the stock width and length are equal to the standard width and length specified by the cost model variables standardPlateLength and standardPlateWidth (4 feet and 8 feet, respectively, in aPriori starting point VPEs)—assuming the part width and length are less than the standard width and length. If the part width and length are greater than the standard, then virtual stock is created that is part width and length plus stock allowances.

Each VPE specifies default values for:

The aPriori starting point VPEs assume non-zero stock allowances for all directions except for the ID stock allowance, which is set to zero.

aPriori also provides process setup options to enable you to override the default stock allowance values for any given part or assembly. To specify a non-default stock allowance value, right-click on the Material Stock process in the Manufacturing Process pane and select Process Setup Options… A window will appear allowing you to edit any or all of the default stock allowance values. See Material Stock Options for more information.