250
Exploring Drafting
is never vertical or horizontal, Figure  10-4.
When associated with a circle or an arc, the
leader always points at or intersects the
primary center of the round feature. In most
cases, a leader is drawn with a small horizontal
tail called a shoulder. When the leader is to
the left of the note, the shoulder connects to
the beginning of the fi rst line of information
associated with the leader. When the leader is
to the right of the note, the shoulder connects
to the end of the last line of information
associated with the leader. The shoulder
typically extends 1/4″ from the leader line. See
Figure 10-5.
Arrowheads for leaders and dimension
lines are drawn freehand and should be care-
fully made, Figure 10-6. The solid arrowhead
is generally preferred. It is made narrower
and slightly longer than the open arrowhead.
For most applications, 1/8″ long arrowheads
are satisfactory. To save time, preprinted (dry
transfer) arrowheads may be applied by the
drafter instead of manually constructing them.
Also, when dimensioning linear distances,
make certain that the tips of the arrows on the
dimension lines touch the extension lines but
do not extend past them. Refer to Figure 10-3.
Types of Dimensions
As previously discussed, the drafter’s
primary concern when dimensioning an object
is to convey the basic information needed to
manufacture the part. For the beginning drafter,
a very basic and easy-to-understand way to
Extension lines are drawn to the same
weight as dimension lines. They extend the
dimension beyond the outline of the view
so that the dimension can be read easily.
Extension lines indicate the beginning and
ending points of linear distances. An extension
line begins 1/16″ away from the point, edge,
intersection, or feature of the object and
extends about 1/8″ past the last dimension
line it is used for. An extension line may
originate within a view and extend across a
view. However, it should not start or stop at
a visible line. Extension lines may cross any
kind of a line except a dimension line. Hence,
it is recommended that smaller dimensions
(size or location dimensions) should be placed
nearest the view, while the larger dimensions
(overall dimensions) should be placed farther
from the view.
Spacing between dimensions in a view may
vary depending on the drawing. Generally,
to avoid crowding, the dimension line for a
dimension should be placed at least 3/8″ from
the object. The spacing between dimensions
should be at least 1/4″.
A leader is another type of dimension line.
It is an angular line used to point out special
characteristics of objects. Leaders are commonly
used to specify sizes of circles and arcs. They
are also used with notes. A leader does not
require extension lines because it usually does
not reference a linear distance. The arrowed
portion of the leader is always angular. It is
inclined at an angle ranging from 15° to 75°
(30°, 45°, and 60° lines are common). A leader
1"max.)
_
16
1" _
8
1"min. _
4
3" _
8
6
Dimension line
min.
Extension line
Extension line offset from object
or object feature (
4
2
Dimension line does not
extend past extension line
Goodheart-Willcox Publisher
Figure 10-3. Lines used for linear dimensioning. Note how dimension and extension lines contrast in thickness
with visible lines.
Copyright Goodheart-Willcox Co., Inc.