Date post: | 03-Jan-2016 |
Category: |
Documents |
Upload: | chastity-rice |
View: | 239 times |
Download: | 1 times |
GTDGTD
Geometric Tolerances and Geometric Tolerances and DimensionsDimensions
Why Geometric Tolerances and DimensioningWhy Geometric Tolerances and Dimensioning To ensure interchangeability of mating parts To ensure interchangeability of mating parts
during assemblyduring assembly
To eliminate controversy and guesswork To eliminate controversy and guesswork when drawing is interpretedwhen drawing is interpreted
To ensure the drawing reflects the form and To ensure the drawing reflects the form and function requirements of the manufactured function requirements of the manufactured partsparts
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
MMCMMC
The actual local size of the hole The actual local size of the hole
atat . 245 . 245 and the pin at and the pin at ØØ .240 .240
of the figure are the Maximum material of the figure are the Maximum material conditioncondition
Ø
LMCLMC
The actual local size of the hole The actual local size of the hole
at at ØØ .255 .255 and the pin at and the pin atØØ .230 .230
of the figure are the least material of the figure are the least material conditioncondition
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)