dimension consists of”
consists of a dimension line, extension lines, arrowheads, and dimension text
dimension line
a thin continuous line terminated by arrowheads that indicate the extend of the dimension
extension lines
project from the feature being dimensiond to the dimension line
extension line rule
DO NOT touch the object outline directly
extension line distance from object + why
1-2mm and extends slightly beyound the dimension line to maintain visual separation
rules for arrowheads under ANSI practice
closed and filled.
uniform throughout the drawing
aligned with the direction of the dimension line
unidirectional dimensioning
all dimension text is oriented horizontally and read from the bottom of the drawing
what does ANSI dimension text orientation require
unidirectional dimensioning
what should you do if space is limited for dimensions text between the extension lines
place it outside the extension lines using a jogged dimension line
where along the dimension line, should the dimension text be placed (as long as space permits)
centered between arrowheads
chain dimensioning + alternative name + do we like it?
places dimensions end-to-end between successive features. each dimension originates from the previous one, forming a chain across the part. there can be one overarching dimension.
series dimensioning
it is generally discouraged
chain dimensioning advantages
simplicity, easy to apply and visuall intuitive, particularly for evenly spaced features
chain dimensioning disadvantages
tolerance accumulation.
tolerance accumulation
individual tolerances add algebraically along the chain (dimensioning), potentially resulting in large overall variation at the end feature
when is chain dimensioning acceptable
noncritical features, cosmetic elements, or features where accumulated variation does not affect assembly or function
baseline dimensioning
measures all features from a common reference line, known as the baseline or datum line
baseline dimensioning advantages + ideal for ?
elimination of tolerance stack-up. functional layouts, hole patterns, and features that must maintain preceise relative positions
baseline dimensioning disadvantages
visual clutter
ordinate dimensioning other name
coordinate
ordinate dimensioning
specifies feature locations using X and Y coordinates relative to a single origin
if ordinate dimensioning doesn’t use arrowheads, what do they do?
use leaders pointing to features with numerical values listed from the origin
ordinate dimensioning advantages + best used for?
compatible with CNC machining, absolute control of feature location with zero tolerance accumulation
hole patterns, machined plates, and parts produced on CNC equipment
ordinate dimensioning disadvantage
if origin is not carefully defined or coordinates are misinterpretated, you get serious manufacturing errors
default unit for metric ANSI drawings
millimeters
