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E112 | W6L11: Dimensions & Tolerances - Coggle Diagram
E112 | W6L11: Dimensions & Tolerances
Dimensions in Drawings
Types of Dimensioning
Dimensioning Small Features
Dimensioning of Multiple Features
Combined Dimensioning
Dimensioning of Radius
Chain Dimensioning
Dimensioning of Circle, Arc, and Hole
Superimposed Running Dimensioning
Dimensioning Angles
Parallel Dimensioning (Datum Dimensioning)
Rules of Dimensioning
Avoid dimensioning to hidden lines and features
Dimension lines, extension lines and object outlines should not cross or overlap
Dimensions should not be duplicated, i.e. same dimension should not be repeated on different views, or the same information need not be given in two different ways
Tolerances
Types of Tolerance
Unilateral Tolerance: allowed to vary in only one direction
Limit Tolerance: the upper and lower limits of the dimension are specified
Bilateral Tolerance: allowed to vary in two directions from the specified dimension. Both directions need not vary by the same amount.
Calculating Tolerance
Tolerance is defined as the difference between the upper limit of a dimension and the lower limit of the dimension. Its formula is given by:
Tolerance = Upper limit – Lower Limit
The Importance of Tolerance
The range of tolerance will translate into the manufacturing method needed, since different manufacturing method has different degree of tolerance.
Same parts can be made from different companies and they have to be interchangeable. Tolerance ensures good quality control for parts from different companies.
If tolerance is not given, exact measurement of the parts must be made. Rejection rate will be very high and is not realistic.
Tolerance will ensure that mating parts of an assembly interface and fit well.
In practice, 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.
Clearance Fit and Interference Fit
Assembling Multiple Parts
In order to bring a product to life, very often, multiple parts and components are needed.
Application of Clearance and Interference Fits
In clearance fit, there would still be an allowance for two parts to move, such as in a door hinge.
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.