a perpendicular to a given line from a given point are

shown in figure 14-9.

1. From point A above line XY, pick any two

points on line XY, such as C and B. Points C

and B can either be on opposite sides of A or

both on the same side of A.

2. With B as a center, and with a radius of BA, draw

short arcs above and below line XY.

3. With C as a center, and a radius of CA, draw

short arcs intersecting the arcs drawn in step 2.

4. Draw line DA through the intersecting arcs.

1. Place a triangle against a straightedge, as shown

Line DA is perpendicular to line XY.

in view A. The hypotenuse of the triangle

should pass through the center of the circle and

the point where the line is to be tangent to the

circle.

Laying out circles or arcs, and straight lines tangent

2. Hold the straightedge firmly in place, and turn

to them, is difficult. It is difficult because there is an

the triangle over.

element of optical illusion involved. Drawing a straight

line to a curved one is easier than drawing a curved line

3. Move the triangle until the hypotenuse passes

to a straight one. Because of this, major circles or arcs

through the point of tangency, and then draw the

are drawn first on layouts.

tangent, as shown in view B.

Even when you draw a straight line to a curve, an

optical illusion may make it difficult for you to blend

the curve and the line perfectly. This section discusses

You may find that when you draw an arc that ends

a few simple methods that should help you to blend lines

in a straight line, you have a tendency to overdraw the

and arcs.

arc (fig. 14-11). Use the following procedure and the

steps shown in figure 14-12 to avoid this.

1. Use any given radius as the distance to set your

dividers.

The draftsman's method of drawing a tangent to a

2. Set one point of the dividers at point A and strike

circle is described in the following steps. It is shown in

tangent points at B and C (view A).

figure 14-10, and you should refer to this figure as you

read this section. You will need your triangle and

3. Without changing the dividers, place one point

straightedge to draw a tangent to a circle.

at B and strike an arc at D.

14-10

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