1. GD&T (Geometric Dimensioning &Tolerancing)
for Engineering Design

2. WWII Revealed Disconnect between Specifications and Manufactured Parts
U.S. National Archives and Records Administration III-NNT-163 NC
Library of Congress, LC-USW
Quandary One:
Many parts manufactured within acceptable tolerances…
did not fit into assemblies overseas.
Library of Congress, LC-USW
Library of Congress, LC-USW
During WWII drafters would manually draw equipment and replacement part for machinery, parts and equipment used in the war. Drawings would include tolerances (i.e. +/- an allowable error). Have students identify similarities and differences between manual and today’s drafting.
2-4) Equipment and methods for producing the parts produced by manufactures and often would be checked to see if these parts were within the tolerances that were verified as acceptable for replacement parts to still fit within assemblies
After discussing stories behind images, bring in Quandary 1: Inspectors would measure parts, many would be allowable range yet NOT work when delivered to replace broken parts within assemblies.
WWII Revealed Disconnect between Specifications and Manufactured Parts

3. Another WWII Era Quandary…
Quandary Two:
WWII Torpedoes
were rejected for not falling within
+/- tolerances…
yet, when fit into submarines functioned?
{{Information |Description={{en|Torpedoes being assembled from completed parts in a factory in the United Kingdom.}} |Source={{IWM Collections|D 392}} |Date=World War II |Author=Ministry of Information Photo Division official photographer |Permission={{PD
Imperial War Museum (United Kingdom) D 392

4. +/- Tolerance Inadequacies
…yet, area from
center is
circular
+/- defines tolerance
as rectangular
Location of Measured
Torpedo Boundary
If necessary, revise earlier theories to better explain Quandaries, which lead to GD&T.

5. GD&T Symbology
Cut out, fold and tape the handout to form a tetrahedron (pyramid).
When you finish,
Review the symbols in
The yellow rectangle. Answer the following:
1) What is the difference between symbols that always, never or some times require datums?
2) Propose examples of features on a part that represents quality.
3) Develop a definition of “controls.” for each of the symbols
authorization use of Tec-Ease resources from their website provided in attachments—note: use as provided by tec-ease, i.e. print as shown on attached tec-ease pdf

6. Function Determines: Design Intent, Datums & More…
Tec-Ease.com at
Prepare a SolidWorks model or use drawing #2 to review design intent, i.e. ask students to identify:
What plane is best to begin this model as shown (right)
What relations and features are most important to preserve when creating different configurations/revisions of the support bracket (symmetry of two holes and material around them, equal size of radii for filleted corners, concentric relations for arc and center of pivot pin hole, which are extruded from mid-plane front plane),
horizontal relationships for centers of circular features and parallel relationship of axis with bottom edge of bracket).

7. Symbology on GD&T Tetrahedron

8. DRF Placement Matters
From Tec-Ease.com at

9. Applying GD&T on 3D Model
Have students complete the following assessment, individually or as part of a group, it is possible that each also include their own assessment of the percentage of provided by each member of their team for each answer. Use attached Assessment Matrix to evaluate competency on these tasks.
Explain purpose, including benefits of GD&T
Describe major reasons design intent is important when creating a 3D Model
Use a student-designed model to
Place feature control frame(s) (FCF) & reference relevant datum(s)
Provide varied and relevant symbology within a feature control frame
Identify datums, give reasons for selecting each datum and for their hierarchy
Justify the geometric characteristic symbol(s) (GCS) used in FCF
Describe way(s) GD&T you used reduces the cost of manufacturing your part
Identify and explain specific way(s) GD&T improves the ability of your part to function within your assembly
Image from Schimmoller, Howard. “Mechanical Model Centric Design at Lockheed Martin.” Lockheed Martin. 24th Congress of International Council of the Aeronautical Sciences, Yokohama, Japan. 1 Sept Web. 27 Aug <
from Schimmoller’s Mechanical Model Centric Design at Lockheed Martin