Geometric Dimensioning and Tolerancing

Lofty goals for the day Define these GD&T terms: FCF, datum, tolerance zone, rule 1, MMC Describe these GD&T characteristics: flatness, parallelism, perpendicularity, circularity, position

MIL-HBK-727

MIL-HBK-727

Basic Dimension Datum Feature Control Frame MIL-HBK-727

(See website listed online)

Datums

Rule 1-Indivdual Feature of Size Where only a tolerance of size is specified, the limits of size of an individual feature prescribe the extent to which variations in geometric form, as well as size, are allowed. (ASTM Y14.5-2009). Meaning?

5±1 6 4 9 10±1 11

Engineering Design Communication – Lockhart and Johnson Fundamentals of Graphics Communication – Bertoline and Weibe

Engineering Design Communication – Lockhart and Johnson Fundamentals of Graphics Communication – Bertoline and Weibe

Engineering Design Communication – Lockhart and Johnson Fundamentals of Graphics Communication – Bertoline and Weibe

Engineering Design Communication – Lockhart and Johnson

Fundamentals of Graphics Communication – Bertoline and Weibe

Position http://www.emachineshop.com/machine-shop/GD-T-Position-Definition/page617.html

Maximum and Least Material Condition (MMC & LMC) MMC – The extreme size of the feature that makes the part weigh the most LMC – The extreme size of the feature that makes the part weigh the least

Hole shown in blue at MMC (d=2.3)

The tolerance zone (.7) is illustrated in black

Four possible holes at MMC with their centers at the boundary of the position tolerance circle are drawn. In order to guarantee functionality, a pin must pass through the circle that overlaps them all possible holes at MMC, with their centers at the boundary of the position tolerance zone. The resulting shape is the Virtual Condition (VC) shown in orange.

SHAFT VC = MMC diameter + Position Tolerance Zone Diameter HOLE VC = MMC diameter - Position Tolerance Zone Diameter

Summary All dimensions include controls of geometry. Rule 1 states that a size control inherently includes controls of form. Because of Rule 1, the need for GDT callouts is minimized. Use carefully. GDT should be used to refine the relationship between feature and form. GDT should open tolerances. MMC should reduce part cost. Technical Graphics Communication, Bertoline, et al

Engineering Design Communication – Lockhart and Johnson Fundamentals of Graphics Communication – Bertoline and Weibe

Engineering Design Communication – Lockhart and Johnson Fundamentals of Graphics Communication – Bertoline and Weibe

Engineering Design Communication – Lockhart and Johnson Fundamentals of Graphics Communication – Bertoline and Weibe

Fundamentals of Graphics Communication – Bertoline and Weibe

Fundamentals of Graphics Communication – Bertoline and Weibe

Regardless of Feature Size (RFS) Maximum Material Condition (MMC)