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Dimensions, tolerance and assemblies - Coggle Diagram
Dimensions, tolerance and assemblies
Dimension
Dimension text: this is the base dimension. Usually the units (mm) are not indicated on every dimension text, but at the bottom corner of the drawing.
Extension line: extension lines 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
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Extension line offset: a gap between the object surface and the extension line, so it is not confused with the visible lines of the model.
Parallel (Datum) dimensioning: consist of several dimensions originating from a common reference surface (datum).
Superimposed running dimension: simplifies parallel dimensions in order to reduce the space used on drawing. Should use only if the function of the object will not be affected by the accumulation of the tolerance.
Chain dimension: should only be used if the function of the object would not be affected by 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 radius: start with capital "R". It shows a radius dimensioned with the center of the radius located on the drawing. Showing how to dimension radii which do not need their centers 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 centre lines.
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Rules
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
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Tolerances
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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Interference Fit
In clearance fit, there would still be an allowance for two parts to move, such as in a door hinge. Maximum shaft diameter is smaller than the minimum hole diameter.
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.
Assembling modelling
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Revolute Joint: Has a single rotational degree of freedom, much like a hinge.
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