maintenance personnel by making it possible for them
to visualize the system or object you are explaining.
BLUEPRINTS AND DRAWINGS
Blueprints are exact copies of mechanical or other
types of drawings and employ a language of their
own. It is a form of sign language or shorthand that
uses lines, graphic symbols, dimensions, and notations
to accurately describe the form size, kind of material,
finish, and construction of an object. It can be said
that blueprint reading is largely a matter of translating
these lines and symbols into terms of procedure,
materials, and other details needed to repair, maintain,
or fabricate the object described on the print.
Usually you can look at a blueprint and recognize
the object if you are familiar with the actual part. But
when you are required to make or check on a certain
part, the applicable blueprint must be referred to in
order to get dimensions and other pertinent
information. The important thing is to know what the
different symbols stand for and where to look for the
important information on a blueprint. Some of the
important facts listed on all blueprints are discussed in
the following paragraphs.
The title block is located in the lower right comer
of all blueprints and drawings prepared according to
military standards. The block contains the drawing
number, the name of the part or assembly that the
blueprint represents, and all information required to
identify the part or assembly.
The title block also includes the name and address
of the Government agency or organization preparing
the drawing, the scale, drafting record, authentication,
and the date (fig. 1-71).
A space within the title block with a diagonal or
slant line drawn across it indicates that the
information usually placed in it is not required or is
given elsewhere on the drawing.
The revision block (not shown) is usually located
in the upper right corner of the blueprint and is used
for the recording of changes (revisions) to the print.
All revisions are noted in this block and are dated and
identified by a letter and a brief description of the
revision. A revised drawing is shown by the addition
of a letter to the original number in the title block, as
shown in figure 1-71, view A. If the print shown in
figure 1-71, view A, was again revised, the letter in
the revision block of the title block would be replaced
by the letter B.
All blueprints are identified by a drawing number
(NAVSHIP Systems Command No. in view A of fig.
1-71, and FEC Drawing No. in view B), which
appears in a block in the lower right corner of the title
block. It may be shown in other places also; for
example, near the top border line in an upper corner,
or on the reverse side at both ends so that it will be
visible when a drawing is rolled up. If a blueprint has
more than one sheet, this information is included in
the block indicating the sheet number and the number
of sheets in the series. For example, note that in the
title blocks shown in figure 1-71 the blueprint is sheet
1 of 1.
Reference numbers that appear in the title block
refer to numbers of other blueprints. When more than
one detail is shown on a drawing, a dash and a
number are frequently used. For example, if two parts
are shown in one detail drawing, both prints would
have the same drawing number, plus a dash and an
individual number, such as 8117041-1 and 8117041-2.
In addition to appearing in the title block, the dash
and number may appear on the face of the drawings,
near the parts they identify. Some commercial prints
show the drawing and dash number, and pint with a
leader line to the part; others use a circle, 3/8 inch in
diameter, around the dash number, and carry a leader
line to the part.
A dash and number are used to identify modified
or improved parts, and also to identify right-hand and
left-hand parts. Many aircraft parts on the left-hand
side of an aircraft are exactly like the corresponding
parts on the right-hand side but in reverse. The
left-hand parts are usually shown in the drawing.
Above the title block on some prints you may see
a notation such as 159674 LH shown; 159674-1 RH
opposite. Both parts carry the same number. But the
part called for is distinguished by a dash and number.
(LH means left-hand, and RH means right-hand.)