1. Geometric Tolerances and Dimensions
GTD
Geometric Tolerances and Dimensions

2. Why Geometric Tolerances and Dimensioning
To ensure interchangeability of mating parts during assembly
To eliminate controversy and guesswork when drawing is interpreted
To ensure the drawing reflects the form and function requirements of the manufactured parts

3. Principles of datum specification
Three perfect plans used to locate an imperfect part.
Three point contact is used on the primary plane.
b. Two point contact is used on the secondary plane.
c. One point contact is used on the tertiary plane

4. datum specification

5. One-Plane Datum Reference Frame

6. Two-Plane Datum Reference Frame

7. Three-Plane Datum Reference Frame

8. Symbols Advantages:
1. The symbol has uniform meaning.
2. Symbols are compact, quickly drawn, and can be placed on the drawing where the control applies.
3. Symbols are the international language and surmount individual language barriers.
4. Geometric tolerance symbols follow the established precedent of other well known symbol systems, e.g., electrical and electronic, welding, surface texture.

9. Using Symbols

10. Using Notes

11. Symbols/Notes

12. Material Condition

15. HOLE
PIN

16. MMC The actual local size of the hole at . 245 and the pin at Ø .240
of the figure are the Maximum material condition Ø

18. LMC The actual local size of the hole at Ø .255 and the pin at Ø .230
of the figure are the least material condition

23. TERMINOLOGY
VIRTUAL CONDITION - A constant boundary generated by the collective effects of a size feature’s specified MMC or LMC and the geometric tolerance for that material condition.

24. VIRTUAL CONDITION Virtual condition, based on MMC or L M C
is a feature‘s extreme boundary; it represents the “worse case”
For MMC, “worse case” concerns fits and/or clearances with mating parts For LMC, “worst case” is concerned with strength, alignment, wall thickness, etc. with reference to mating parts

25. VIRTUAL CONDITION (MMC- PIN)
Virtual Condition for a Pin
(Based on Maximum Material Condition) = Maximum Material Condition + the Stated Position or Orientation Tolerance
VC = MMC + Tolerance

26. VIRTUAL CONDITION (MMC- PIN)

27. VIRTUAL CONDITION (MMC- Hole)
Virtual Condition for a Hole
(Based on Maximum Material Condition) = Maximum Material Condition - the Stated Position or Orientation Tolerance
VC = MMC - Tolerance

28. VIRTUAL CONDITION (MMC- Hole)

29. VIRTUAL CONDITION (LMC- PIN)
Virtual Condition for a Pin
(Based on Least Material Condition) =
Least Material Condition - the Stated Position or Orientation Tolerance
• VC = LMC - Tolerance

30. VIRTUAL CONDITION (LMC- PIN)

31. VIRTUAL CONDITION (LMC- Hole)
Virtual Condition for a Hole
(Based on Least Material Condition) = Least
Material Condition + the Stated Position or Orientation Tolerance
VC = LMC + Tolerance

32. VIRTUAL CONDITION (LMC- Hole)