Information on Feature Control Frame (FCF) Dimension Calculations

PC-DMIS and ASME Y14.5-2009

• PC-DMIS GD&T supports the ASME Y14.5-2009 standard. The mathematics for this standard are described in "ASME Y14.5.1M-1994 Mathematical Definition of Dimensioning and Tolerancing Principles". To support the 2009 standard, PC-DMIS provides the following:

• You can customize the Datum Reference Frame (DRF) in the FCF. For information, see "Using Maximum Material Boundary (MMB) and Least Material Boundary (LMB)".

• You can define the Maximum Material Boundary (MMB) value inside a datum's brackets in a FCF when you choose a modifier. For information, see "Creating Customized Datum Reference Frames".

• You can select a Circle-U symbol for unequally dispersed tolerance zones. For information, see "Using Unequal Tolerance Zones with Profile Feature Control Frame Dimensions".

Profile Calculations

• In v4.2 and higher, in the Option section of the PC-DMIS Settings Editor, you can set the UseISOCalculations registry entry to 1. This reports Profile as two times the maximum deviation. This setting only affects Profile (not Flatness). Also, when the GD&T Standard on the Feature Control Frame tab of the GD&T dialog box is set to ISO 1101, the Profile reports two times the max deviation, and Profile form only ignores size.

• In PC-DMIS 2009 and higher, FCF Profile with no datum referenced takes into account size. The UseSizeForProfileDimensions registry entry in the Option section of the PC-DMIS Settings Editor lets you revert to the V42 and earlier behavior for legacy profile dimensions only. This registry entry defaults to 1 (TRUE), so you must use the PC-DMIS Settings Editor to change it to 0 (FALSE). If set to 0, legacy Profile form only ignores size. However, the FCF Profile always takes size into consideration.

Some Calculation Differences

• PC-DMIS computes Legacy dimensions for Roundness, such as a Location dimension's RN line or a legacy Circularity dimension, with the Least Square solution. On the other hand, it computes FCF dimensions for roundness (Circularity and Cylindricity) in version 4.2 and higher with the Tchebychev algorithm (min/max) as required by the Y14.5 standard. Because of the change in calculation, Circularity and Cylindricity FCF dimensions generally compute to a slightly smaller value than their legacy counterparts.

Form Calculations

• FCF dimensions in PC-DMIS 4.2 and later support the Y14.5 definitions of Circularity and Cylindricity.

• FCF dimensions in PC-DMIS 4.3 and later support the Y14.5 definitions of Flatness. FCF flatness uses a Tchebychev (min/max) algorithm. Legacy flatness still uses the LS method. FCF flatness generally gives a somewhat smaller flatness value than the LS flatness. This is independent of the UseISOCalculations registry entry.

• FCF dimensions in PC-DMIS 2009 and later support the Y14.5 definition of Straightness when using FCF dimensions.

• Legacy form dimensions still calculate the least squares form.

A Note on Parallelism Evaluation

• The evaluation of parallelism is 3-dimensional regardless of the workplane or the feature being dimensioned.