Lesson 6

Lesson 6

Assemblies

Assembly Modeling

Joints

Ball

Planar

Pin Slot

Cylindrical

Slider

Revolute

Single rotational degree of freedom like a hinge

Rigid

Joins 2 components together no movements

Fitting

Interference Fit

There will always not be enough clearance for the shaft to fit

Difficult to move or remove

Shat is bigger than the hole

Clearance FIt

There will always be enough clearance for the shaft to fit

Allows 2 parts to move

Shaft is smaller than the hole

e.g. door hinge

Tolerance

Calculating Tolerance

Upper limit - Lower limit

3 Types of Tolerance

Limit

The upper and lower limits of the dimension

Unilateral

Vary in only 1 direction

Bilateral

Vary in 2 directionn many not be the same amount of tolerance

The importance

Ensure the parts will fit well

To ensure parts form diffrent companies are interchangeble

ensure quality control for parts form different companies

To identify the manufacturing method needed

Prevent high rejection rates

Dimensions

Rules

Dimension lines, extension lines and object outlines sould not cross or overlap

Avoid dimensioning to hidden lines and features

NO duplicate dimensions

Dimension Lines

Toloerance

Define how much deviation from the dimension is allowed

Dimension Text

Base dimension (mm)

At the bottom corner of the drawing

Dimension Line

Has an arrowhead on each end

Extension Line

Extended line form the surface of the object to establish the size of the dimensions

Extension Line offset

The gap between object and extension line

Dimensioning

Angles

Marked with curved dimension line and has a degree symbol

Circle, Arc and Hole

Hole

located by their centerlines

Arc

Circle

Diameter

Radius

Starts with R

Just dimension is center is not needed

Line to indicate centre start form centre

Multiple Features

Use N x Dimension for multiple same dimensions

Small Features

Arrowheads place outside the extension lines

Combined

Uses both Chain and parallel dimensioning

Chain

Should only be used if the function of the object will not be affected by accumulated tolerances

Indicates the dimensions individually

Superimposed Running

Simplifies dimensions to reduce the space used on a drawing

Parallel/Datum

consist of several dimension origination from a common reference aka datum