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Linear Extruded Features
(In accordance with the ASME Y14.5-2009 standard)

PDF of this Tip

The 1994 revision of the ASME Y14.5 standard provided a couple of options for controlling irregular shapes such as ’D’ and ’double D’ shaped features.  The 2009 revision named these features linear extrusions which is a math term and is not referring to the process used to create the feature.  I am often asked how to control these features so I will summarize the methods in this Tip.  One person who asked said he was reluctant to do it in accordance with the Standard because "it could raise more questions internally during the drawing review process and because those reviewing the drawings are not used to seeing it."  Well, the only people who like change are wet babies but if you never change, you can never improve.  This is today’s print reading.  If you are making or inspecting prints, you better know how to read the print.

On this drawing I have used the two common methods of controlling these types of features.  In both cases, the size and form of the feature is controlled by the profile of a surface tolerance in the upper segment as a directly toleranced dimension does on a regular feature of size such as a hole.  The location and orientation of the features are controlled by the lower segment which includes datum feature referencing.

The ’D’ shaped hole on the left is using two profile tolerances.  This provides two sets of boundaries that the feature must not violate.  The size and form tolerance of 0.2 is centered on the Ø20 mm and the 7 mm dimensions but is free to float relative to the datum reference frame.  The feature may float around provided it does not violate the boundaries established by the 0.6 tolerance that is center on the Ø20 mm and the 7 mm dimensions and located at the basic location from the datum reference frame.

The ’double D’ hole on the right is located by the position tolerance.  This is a nice approach to take where it is desirable to hard gage the location of the feature.  The only requirement made by the position tolerance is that the surface of the feature does not violate a maximum material boundary (inner boundary) with a width of 13.2 mm (14 - 0.2 - 0.6) and a Ø of 19.2 mm (20 - 0.2 - 0.6) that is at the basic location from the datum reference frame.

Both approaches are in accordance with the ASME Y14.5-2009 standard.

Back to Tips Tip added Feb 2014