parallel and in contact with the edge of the drawing table to ensure
consistent horizontal lines.
(2) Straightedges and triangles (figure 18(B)). You use
straightedges and triangles to draw straight lines between two points on
the drawing with no change in direction between the two points. You use
both straightedges and triangles and they are made of either plastic or
wood and come in various sizes. Occasionally, you use a straightedge as
a cutting guide when cutting thick illustration board. Never use a
plastic straightedge as a cutting guide. You can damage the edge of the
straightedge and it will no longer create flawless lines.
You use the triangles to draw vertical lines on the drawing surface by
resting the base of the triangle on the T square. You also can use the
triangle to draw 45 and 60 angles or put the two triangles together to
make increments of 15.
(3) Rulers and scales (figure 18(C)). Rulers and scales provide
a means of measuring different distances on the drawing surface. They
have different graduations for different applications such as
engineering, technical drawing, or drafting. Their intended use
determines the graduation scale, 32nd, 16th, and 10th of an inch, or
they could measure metrics and have graduations in millimeters,
centimeters, or decimeters. Usually you find scales shaped triangularly
and rulers flat. You should never use a scale as a cutting guide.
(4) Protractors (figure 18(D)). You see round, halfround, or
square protractors used to draw graphics. No matter what shape they
have, they all have degrees marked on them. You can use protractors to
measure and create simple azimuths or angles, construct pie charts, etc.
(5) Compasses (figure 18(E)). When creating a graphic, you use a
compass to draw arcs and circles. A compass has a handle in the center,
a metal point at one end, and either a pencil or pen at the other. When
using the compass to draw a circle or arc, place the metal point at the
center of the arc or circle, slightly lean the compass in the direction
you are drawing, and pull the compass to draw the arc or circle.
(6) Erasing shields (figure 18(F)). Erasing shields, made from
stainless steel, have patterns cut in them. You use the erasing shield
to localize the mistake so you do not remove any of the good area.
Place the cutout pattern that most closely resembles the area to be
erased so you can only see the mistake in the pattern; then erase your
mistake.
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