GD&T Fundamentals - Course Outline

Recommended Prerequisites:

  • Validate-3D LLC Drawing Practices

 Learning Objectives:

  1. Identify the shortcomings of “plus/minus” tolerancing for orientation or location control.
  2. Describe why GD&T has been developed.
  3. Define the significance of the Envelope Principle and size tolerance concepts defined in ASME Y14.5 and describe common industry practice regarding the requirements of size tolerances.
  4. Apply the concepts needed to properly establish a function-based datum reference frame for mechanical parts per the concepts defined in ASME Y14.5, including the selection and labeling of datum features and datum targets, concepts of datum feature simulators, datums, a datum reference frame, and tolerancing of datum features.
  5. Understand and apply tolerances with modifiers and labels, if applicable, as defined in ASME Y14.5.
  6. Apply feature pattern tolerance refinement methods from ASME Y14.5.
  7. Identify how knowledge of GD&T concepts can lead to improved design of mechanical assemblies.
  8. Effectively decode GD&T specifications and identify associated measurement data reporting needs to address those specifications.

 Course Topics:

This course is guided by mechanical assembly examples - We will be learning as we apply GD&T in progressively less simple cases with side topics as needed for:

  • Definitions of GD&T Terms
  • Explanation of GD&T Concepts
  1. Example parts 1 and 2 - Terms and concepts covered:
  • Feature
  • Form/Size/Orientation/Location (the 4 types of geometric control)
  • Feature of size
  • Size tolerance
  • Unrelated Actual Mating Envelope
  • Local Size
  • Maximum Material Condition (MMC) and Least Material Condition (LMC)
  • Envelope principle and “Rule #1” from ASME Y14.5
  • Feature control frames for form controls
  • Circularity tolerance
  • Cylindricity tolerance
  • Limits and Fits
  • Measurement data reporting practices for size tolerances
  • Perpendicularity of a surface
  • Feature control frames for orientation and location controls
  • Basic dimensions
  • Measurement data reporting practices for perpendicularity of a surface.
  • Datum reference frame
  • Datum
  • Datum feature
  • Datum feature simulator
  • Regardless of Material Boundary (RMB), Maximum Material Boundary (MMB), and Least Material Boundary (LMB)
  • Using datum features, their datum feature simulators, and concepts from ASME Y14.5 to establish simulated datums and the associated datum reference frame
  • Tolerancing datum features
  1. Example part 3 - Terms and concepts covered:
  • More on DRFs and all associated terms
  • Flatness tolerance applied to a surface
  • Measurement data reporting for flatness
  • Perpendicularity tolerance applied to a feature axis
  • Measurement data reporting for perpendicularity of a feature axis
  • Position tolerance applied to a feature axis at RFS
  • Coordinate axes to represent a datum reference frame
  • Measurement data reporting for position of a feature axis at RFS
  • Location components
  • Position of a feature axis at MMC
  • Measurement data reporting for position of a feature axis at MMC
  • Perpendicularity, parallelism, or angularity tolerance applied to a feature axis as a refining orientation control
  • Zero tolerance value at MMC/LMC
  1. Example parts 4 and 5 – Terms and concepts covered:
  • The Continuous Feature modifier applied to form tolerances
  1. Modified version of example part 3 – Terms and concepts covered:
  • The Continuous Feature modifier applied to orientation tolerances
  1. Revised version of example part 5 to eliminate example parts 3 & 4 – Terms and concepts covered:
  • Tolerance stacks and the looser tolerances enabled by combining parts
  1. Example parts 6 and 7 – Terms and concepts covered:

Regardless of Material Boundary

  • Maximum Material Boundary, Least Material Boundary, and BSC concepts for datum feature simulators
  1. Example parts 8 and 9 – Terms and concepts covered:
  • Straightness tolerance applied to a derived median line at Regardless of Feature Size (RFS)
  • Straightness tolerance applied to surface lines
  • Measurement data reporting for straightness of a derived median line at RFS
  • Measurement data reporting for straightness of surface lines
  1. Example parts 10 and 11 – Terms and concepts covered:
  • Best practices for tolerancing a conical surface
  • Profile of a surface tolerance
  • Surface deviations
  • Measurement data reporting for profile of a surface
  1. Revision of example part 5 – Terms and concepts covered:
  • Basic dimension information in tabular format for profile of a surface tolerances applied to complex surfaces
  1. Revision of example part 5 and addition of example part 12 – Terms and concepts covered:
  • Circular runout tolerance
  • Total runout tolerance
  • Measurement data reporting for circular runout and total runout tolerances
  1. Example part 13 – Terms and concepts covered:
  • Datum reference frame with a rotational degree of freedom left unconstrained
  • Position tolerance with best-fitting required
  • Best choice of datum features
  1. Revision of example part 5 (make it a rough casting) – Terms and concepts covered:
  • Datum features referenced at least material boundary (LMB)
  • Position tolerance applied to a feature at LMC (resolved geometry method and surface method)
  • Datum target points, lines and areas
  1. Example parts 14, 15, and 16 – Terms and concepts covered:
  • Customized datum reference frames
  • Composite feature control frames (for position tolerances or profile tolerances)
  1. Example part 17 – Terms and concepts covered:
  • Part restraint for measurement
  • Free state modifier

Do you have any QUESTIONS about this course?

About Your Trainer:

Dean Watts has been providing Geometric Dimensioning and Tolerancing (GD&T) training and consulting since 1999.  Prior to his engineering education he worked in production machining, precision sheet metal, and TIG welding.  He is an American Society of Mechanical Engineers (ASME) Senior Level GD&T Professional (ASME GDTP S-0295).  He is a member of three ASME standards development committees: ASME Y14.5 “Dimensioning and Tolerancing", ASME Y14.8 “Castings Forgings and Molded Parts”, and ASME Y14.45 “Measurement Data Reporting” (Chair).  He holds BSIE and MSME degrees from Oregon State University.  He taught ME 411/511, a GD&T fundamentals course, for 10 years as an adjunct faculty member at Oregon State University.  He is also a former U.S. Navy Submarine Warfare Officer, and retired U.S. Coast Guard Reservist.

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