PRIN. OF DRAFTING AND SHOP DRAWINGS - OD1641 - LESSON 1/TASK 2
accurate than one-sixteenth must
be
estimated.
For
example,
1/32
is
halfway
between the 0 and the 1/16 marks.
Figure 17 (on the previous page) shows part of a decimal scale.
Each inch is
divided into 50 equal parts making it possible to make measurements within 0.01
inch (hundredth of an inch) accuracy.
Several sample readings have been included
and the first 0.10, unlike a real decimal scale, has each graduation mark labeled.
Many scales are set up for other than full-sized drawings.
For example, the 1/2
scale enables a half-sized drawing to be made directly without having to divide
each dimensional value by 2. Three-quarter scales enable direct 3/4 sized drawings
to be made, and so on.
All fractional scales are read as shown in figure 18.
Only one of the sections
representing an inch is graduated into fractional parts. This graduated section is
located to the left of the "0" mark. When making a reading (for example 3 7/8) on
a fractional scale, read the whole (3) part of the number to the right of the "0"
and the fractional part (7/8) to the left. See figure 18 for an example of a 3 7/8
reading on a half-scale.
FIGURE 18.
A HALF SCALE WITH SOME
SAMPLE MEASUREMENTS.
22
Previous Page
