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L6 Dimensions, Tolerances, Assemblies - Coggle Diagram
L6 Dimensions, Tolerances, Assemblies
Dimensions in drawings
1) Dimension Text: A base dimension, units are in mm It is not indicated on every dimension text, but at the bottom of the drawing.
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4) Extension Lines: They are lines that continue 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.
5) Extension line offset: It is a gap between the object surface and the extension line, so it is not confused with the visible lines of the model.
Types of dimensioning
Parallel Dimensioning (Datum dimensioning): Consists of several dimensions originating from a common reference surface (also known as datum)
Superimposed running dimensioning: Simplifies parallel dimensions in order to reduce the space used on a drawing.
Chain Dimensioning: Should only be used it the function of the object would not be affected by the accumulation of the tolerances.
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Dimensioning small features: Placing arrow heads between the extension lines may make the dimension very difficult to read. Arrow heads can be placed outside the extension lines instead.
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Dimensioning of radius:
(a) shows a radius dimensioned with the centre of the radius located on the drawing. (b) shows how to dimension radii which do need their centres locating.
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
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Rules of Dimensioning:
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
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Dimension lines, extension lines and object outlines should not cross or overlap
Tolerance
Importance of tolerance: 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.
- If tolerance is not given, exact measurement of the parts must be made. Rejection rate will be very high and is not realistic.
- 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.
- Tolerance will ensure that mating parts of an assembly interface and fit well.
Types of tolerance:
Bilateral Tolerance- allowed to vary in two directions from the specified dimension.
Bothe directions need not vary by the same amount.
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Assembly modelling
In an assembly model, multiple parts are brought together to define a larger, more complex product representation. Assembly modelling facilitates the collaboration among designers, engineers, manufacturing technicians and others to ensure a product assembly works. Individuals in different disciplines can work concurrently, resulting in faster and less costly delivery of products to market.
Joints in fusion 360:
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Revolute Joint: Has a single rotational degree of freedom, much like a hinge.