Lesson 6
Dimensions
Dimensioning
Parallel/Datum
consist of several dimension origination from a common reference aka datum
Superimposed Running
Simplifies dimensions to reduce the space used on a drawing
Chain
Indicates the dimensions individually
Should only be used if the function of the object will not be affected by accumulated tolerances
Combined
Uses both Chain and parallel dimensioning
Small Features
Arrowheads place outside the extension lines
Multiple Features
Use N x Dimension for multiple same dimensions
Radius
Starts with R
Line to indicate centre start form centre
Just dimension is center is not needed
Circle, Arc and Hole
Circle
Diameter
Arc
Radius
Hole
located by their centerlines
Angles
Marked with curved dimension line and has a degree symbol
Dimension Lines
Extension Line offset
The gap between object and extension line
Extension Line
Extended line form the surface of the object to establish the size of the dimensions
Dimension Line
Has an arrowhead on each end
Dimension Text
Base dimension (mm)
At the bottom corner of the drawing
Toloerance
Define how much deviation from the dimension is allowed
Rules
NO duplicate dimensions
Avoid dimensioning to hidden lines and features
Dimension lines, extension lines and object outlines sould not cross or overlap
Tolerance
The importance
Prevent high rejection rates
To identify the manufacturing method needed
To ensure parts form diffrent companies are interchangeble
ensure quality control for parts form different companies
Ensure the parts will fit well
3 Types of Tolerance
Bilateral
Vary in 2 directionn many not be the same amount of tolerance
Unilateral
Vary in only 1 direction
Limit
The upper and lower limits of the dimension
Calculating Tolerance
Upper limit - Lower limit
Assemblies
Fitting
Clearance FIt
There will always be enough clearance for the shaft to fit
e.g. door hinge
Shaft is smaller than the hole
Allows 2 parts to move
Interference Fit
There will always not be enough clearance for the shaft to fit
Shat is bigger than the hole
Difficult to move or remove
Assembly Modeling
Joints
Rigid
Joins 2 components together no movements
Revolute
Single rotational degree of freedom like a hinge
Slider
Cylindrical
Pin Slot
Planar
Ball