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

2. 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

3. 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).

4. 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?

5. 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.

6. 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

7. 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.

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

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

10. 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.

11. 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 


12. 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

13. 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

14. 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.”

15. 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

16. Features of Size Rule #1 – “Size Controls Form”
Established by Mil-Std
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

17. 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

18. 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

19. 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

20. 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)

21. 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

22. 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

23. 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

24. 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

25. 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.

26. 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.

27. 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.

28. 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

29. 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

30. GD&T Resources Applied Geometrics, Inc. Tec-Ease, Inc. 497 Lyon Blvd.
South Lyon, MI
(248)
Tec-Ease, Inc.
29 Curtis Place
Fredonia, NY
(888)