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All drawings can be classified as either
drawings with scale or those not drawn to scale. Drawings
without a scale usually are intended to present only
functional information about the component or system. Prints
drawn to scale allow the figures to be rendered accurately
and precisely. Scale drawings also allow components and
systems that are too large to be drawn full size to be drawn
in a more convenient and easy to read size. The opposite is
also true. A very small component can be scaled up, or
enlarged, so that its details can be seen when drawn on
paper.
Scale drawings usually present the
information used to fabricate or construct a component or
system. If a drawing is drawn to scale, it can be used to
obtain information such as physical dimensions, tolerances,
and materials that allows the fabrication or construction of
the component or system. Every dimension of a component or
system does not have to be stated in writing on the drawing
because the user can actually measure the distance (e.g.,
the length of a part) from the drawing and divide or
multiply by the stated scale to obtain the correct
measurements.
The scale of a drawing is usually presented
as a ratio and is read as illustrated in the following
examples.
1" = 1" Read as 1 inch (on the
drawing) equals 1 inch (on the actual component or system).
This can also be stated as FULL SIZE in the scale block of
the drawing. The measured distance on the drawing is the
actual distance or size of the component.
3/8" = 1' Read as 3/8 inch (on the
drawing) equals 1 foot (on the actual component or system).
This is called 3/8 scale. For example, if a component part
measures 6/8 inch on the drawing, the actual component
measures 2 feet.
1/2" = 1' Read as 1/2 inch (on the
drawing) equals 1 foot (on the actual component or system).
This is called 1/2 scale. For example, if a component part
measures 1-1/2 inches on the drawing the actual component
measures 3 feet.
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