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Dimensions,
Tolerances
&
Assemblies - Coggle Diagram
Dimensions,
Tolerances
&
Assemblies
Dimensions
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Extension Line
Continues or extend from the surface of the object and establish the size of the dimension. They do not touch the object lines and extend slightly past the dimension line.
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Types of Dimensioning
Parallel Dimensioning(Datum Dimensioning)
-Consists of several dimensions originating from a common reference surface.
Superimposed Running Dimensioning
-Simplifies parallel dimensions in order to reduce the space used on a drawing.
Chain Dimensioning
-Should only be used if the function of the object would no be affected by the accumulation of the tolerances.
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Dimensioning Small Features
-Arrow heads should be placed outside the extension lines instead of between them.
Dimensioning of Multiple Features
-To dimension multiple same dimensions use N x Dimension
Dimensioning of Radius
-Radial dimensions start with Capital 'R'
(a) Shows a radius dimensioned with the centre of the radius located on the drawing
(b) Shows how to dimension radii which do not need their centres locating.
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Dimensioning of Circle, Arc and hole
-A circle is dimensioned by its diameter
-An arc is dimensioned by its radius.
-Holes are located by their centerlines.
Rules of Dimensioning
-Dimensions should no be duplicated
-Avoid dimensioning to hidden lines and features
-Dimensions lines, extensions lines and object outlines should not cross or overlap.
Tolerances
Importance of Tolerance
Since parts cannot be manufactured exactly to the dimensions stated in the drawing, due to manufacturing variations. Tolerances are included with dimensions in engineering drawings to take into account these manufacturing limitations.
Types of Tolerances
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Bilateral Tolerance
Allowed to vary in two directions from the specified dimension. Both directions need not vary by the same amount
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Assemblies
Type of Fits
Interference Fit
-Where there is insufficient clearance for an object to fit in another
-In interference fit, it would be difficult to move ( or remove ) the two interfacing parts. Usually, a lot of force is needed to remove the two parts. Examples are shafts that are fitted through bearings, so that the shaft does not slip.
Clearance Fit
-Where there is sufficient clearance for an object to fit in another.
-In clearance fit, there would still be an allowance for two parts to move, such as in a door hinge
What is Assembly Modelling?
-It is where multiple parts are brought together to define a larger, more complex product representation. Assembly modelling facilitates the collaboration among people and ensure a product assembly works.
How Assembly Modelling Works?
It works by bringing in a base component that has a central role. Each component in the brought in needs to be oriented and located relative to other components in the assembly. Assembly joints are used between elements of components.
Example of Assembly Drawing
Type of Joints
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Revolute Joint
Has a single rotational degree of freedom, much like a hinge.