ASME Y14.5 Dimensioning and Tolerancing HEATING, COOLING & WATER HEATING PRODUCTS ASME Y14.5 Dimensioning and Tolerancing Steve Miles, Quality Improvement Manager

Overview The Simplest Part in the World Geometric Dimensioning & Tolerancing ASME Y14.5 Datum Reference Frames Features of Size GD&T Symbols Feature Control Frames Metrology Considerations SPC Considerations

The Simplest Part in the World 3.000  .010 1.000  .005 Parts were ordered from Supplier A and Supplier B. The parts from Supplier A worked fine, but those from Supplier B didn’t work about 10% of the time. Parts from both suppliers were measured with calipers and everything checked out OK (length and diameter were within specification).

The Simplest Part in the World 3.000  .010 1.000  .005 From the exaggerated view above, it is easy to see why some of the parts didn’t work – they were not straight! So how did the “bad” pins pass inspection? How straight is good enough? Is that requirement clear from the drawing in the previous slide?

Geometric Dimensioning & Tolerancing GD&T is a precise mathematical language that controls the size, form, orientation and location of part features. It is also a design-dimensioning philosophy that encourages designers to define a part based on how it functions in the final product. GD&T has been developing over the past 80 years or more, but began to see much more application after WWII.

Geometric Dimensioning & Tolerancing Some benefits of GD&T: Depicts functional design relationships Provides a common language for design, production, and inspection Ensures part interchangeability Allows consistent part inspection Facilitates the creation of functional gaging Permits maximum use of available tolerances Compatible with CAD systems

ASME Y14.5 AMSE Y14.5 establishes uniform practices for stating and interpreting dimensioning, tolerancing, and related requirements for use on engineering drawings and in related documents. AMSE Y14.5 is the preferred standard for GD&T in the U.S. and several foreign countries because of its stability, emphasis on design intent, mathematical definition, and translation into several languages. The ISO parallel (not equivalent) is ISO 1101.

Datum Reference Frames Where is the center of the part in the drawing above?

Datum Reference Frames Where is the center of the production part shown above?

Datum Reference Frames Datum – Theoretically exact point, axis, line, plane, or combination thereof derived from the theoretical datum feature simulator. Datum Reference Frame – Three mutually perpendicular intersecting datum planes which constrain degrees of freedom and establish relationships imposed by geometric tolerances.

Datum Reference Frames Datum Identification: Capital letter (except I, O, or Q) enclosed in a square or rectangular frame and a leader line extending from the frame to the feature, terminating with a triangle (filled or not filled)  2.00  

Datum Reference Frames Degrees of Freedom Translation Along X Axis Along Y Axis Along Z Axis Rotation About X Axis About Y Axis About Z Axis X Y Z

Datum Reference Frames Typical Datum Features: Planar (Nominally Flat) Constrains up to 3 degrees of freedom – 1 Translation and 2 Rotation Width (Two Opposed Parallel Surfaces) Cylindrical Constrains up to 4 degrees of freedom – 2 Translation and 2 Rotation Spherical Constrains up to 3 degrees of freedom – 3 Translation

Datum Reference Frames How do we determine which degrees of freedom are constrained by a particular datum feature simulator? Consideration must be given to the datum’s position in the DRF, i.e. primary, secondary or tertiary. CAN, MAY, MUST Rule: “If it can, and it may, then it must.”

Features of Size Features of Size: “Caliper Rule” Courtesy of Tec-Ease Directly toleranced dimension Contain opposing points Have a reproducible derived median point, axis, or center plane “Caliper Rule” Courtesy of Tec-Ease Internal FOS External FOS Not a FOS

Features of Size Rule #1 – “Size Controls Form” Established by Mil-Std 8 1949 Unless otherwise specified, the form of an individual regular feature of size is controlled by its limits of size. Requires perfect form at MMC (or LMC) Exceptions: Stock, e.g. bars, sheets, tubing, etc., produced to established industry or government standards Parts subject to free-state variation in the unrestrained condition, i.e. flexible parts

Features of Size Rule #1 – “Size Controls Form” 1.000  .005 Rule #1 requires that the entire surface of the pin fall within the maximum material condition of 1.005. 1.005

GD&T Symbols - Form Form Tolerances: Straightness () Flatness () Circularity () Cylindricity () Apply to single features, elements of single features, or features of size Not related to datums

GD&T Symbols - Orientation Orientation Tolerances: Angularity () Parallelism () Perpendicularity () Apply to a feature, its line elements, its axis, or its center plane Must be related to one or more datums

GD&T Symbols - Location Location Tolerances: Position () Concentricity () Symmetry () Apply to features of size Normally related to one or more datums (exception is position of two coaxial features)

GD&T Symbols - Profile Profile Tolerances: Profile of a Line () Profile of a Surface () Apply to an entire part, multiple features, individual surfaces, or to individual profiles taken at various cross sections through a part May or may not be related to datums, depending on the design requirements

GD&T Symbols - Runout Runout Tolerances: Circular Runout () Total Runout () Apply to surfaces constructed around a datum axis and those constructed at right angles to a datum axis Must specify the datum axis

GD&T Symbols - Modifiers Material Condition Modifiers: MMC, Maximum Material Condition () Ex: Smallest hole or largest pin LMC, Least Material Condition () Ex: Largest hole of smallest pin Apply to features of size RFS, Regardless of Feature Size, is implied where no modifying symbol is specified

Feature Control Frames Applied to a feature or group of features Include a geometric characteristic symbol and its associated tolerance value Datum references are added as required Modifiers may be applied to the tolerance and datum reference frame as appropriate Example: 030

Feature Control Frames Tolerance Value (always total) Datum Reference Frame Geometric Characteristic Symbol 030 Tolerance Zone Shape Tolerance Modifier Boundary Modifier The feature’s axis is to be positioned within a cylindrical tolerance zone of .030 in diameter when the feature is produced at its MMC with respect to datums A primary, B secondary (at MMB) and C tertiary.

Feature Control Frames Decode the following: 030 The surface must be flat within a total width tolerance zone of .030. 030 The surface must be parallel to datum A within a total width tolerance zone of .030. 030 The surface must fall within a total width tolerance zone of .030 from its true profile relative to datum A primary, B secondary and C tertiary.

Class Exercise Using the drawings provided, identify the features of size and the geometric tolerances. Be prepared to decode and discuss the feature control frames. Be prepared to discuss possible measurement methods for each characteristic.

Metrology Considerations Basic dimensions (generally enclosed in a box) do not require evaluation Features of Size require: Check for Actual Mating Size Checks for Local Size “Best-fitting” will often be used by measurement software in the construction of the DRF and for optimizing all of the measured deviations Reporting of total width vs. deviated distance Rule of Simultaneous Requirements

SPC Considerations Many geometric characteristics may have non-normal distributions, e.g. flatness and position Zero as a boundary vs. LSL Statistical tolerancing () requires appropriate statistical process control Material condition modifiers provide bonus tolerance, but are often process independent Additional measures, e.g. Δx and Δy, may be helpful in controlling some processes “Zero tolerance” callouts, e.g. 0

GD&T Resources Applied Geometrics, Inc. Tec-Ease, Inc. 497 Lyon Blvd. South Lyon, MI 48178-1235 (248) 486-9011 www.gdandt.com Tec-Ease, Inc. 29 Curtis Place Fredonia, NY 14063 (888) 832-3273 www.tec-ease.com