You can define or import geometric and dimensional tolerances (GD&T) and surface roughness requirements for GCDs. If you do not define any of these values, none are assumed - aP Pro does not set default desired tolerances. These values affect the cycle time to complete an operation; for example, if lower finish machining feed rates are required to achieve tighter (smaller) tolerance values, this increase cycle times.
When aP Pro costs a GCD, it selects only those processes and operations matching the requirements for that GCD. If the primary process group cannot meet these requirements, aP Pro selects secondary machining operations. If no suitable secondary machining operations are available, the GCD fails to cost.
Important: You do not need to set tolerances for every GCD. For a given GCD, you only need to set tolerances that are close to or tighter than the achievable tolerances of the process aP Pro chooses for the GCD.
Set Tolerance Values
You can set tolerance and roughness requirements for a GCD:
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Manually: setting policy values for all GCDs in a component, using the Tolerance Policy Editor. See Use the Tolerance Policy Editor.
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Manually: setting values for specific GCDs, either using the Tolerance Editor or using the Geometric Cost Drivers panel. See Manually Edit Tolerance Values.
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Automatically: Importing semantic PMI annotations directly from the CAD model. See Import PMI from CAD.
Tolerance Setting Guidance
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aPriori stores and displays tolerance values as total tolerance. For example, if a CAD system specifies a tolerance of ±0.25, you should enter the total tolerance 0.5. If you import a tolerance from a PMI attribute, aPriori displays it as a total tolerance.
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For Stock Machined components, only enter total tolerances of 0.004in (0.1016mm) or less.
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For roughness, identify your main machining process type (milling or turning) in the table below, and enter only roughness values that are within +25% or less of the best achievable roughness for that process type. The following table shows aPirori default roughness capabilities:
Process Name
Best Achievable Roughness (µm)
Roughness (µin)
Milling
0.8
31.5
Turning
0.4
15.75
Tip: For more details about how aP Pro calculates and uses tolerances, see Tolerance Specifications and Calculations.