3.GTD.4210

Report
GTD
Geometric Tolerances and Dimensions
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
Principles of datum specification
Three perfect plans used to locate
an imperfect part.
a. 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
datum specification
One-Plane Datum Reference Frame
Two-Plane Datum Reference Frame
Three-Plane Datum Reference Frame
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.
Using Symbols
Using Notes
Symbols/Notes
Material Condition
•
HOLE
PIN
MMC

The actual local size of the hole
at Ø . 245 and the pin at Ø .240
of the figure are the Maximum material
condition
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
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.
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
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
VIRTUAL CONDITION (MMC- PIN)
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
VIRTUAL CONDITION (MMC- Hole)
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
VIRTUAL CONDITION (LMC- PIN)
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
VIRTUAL CONDITION (LMC- Hole)

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