Cad Guidebook: A Basic Manual for Understanding and Improving Computer-Aided Design (21 page)

Finally, many CAD systems allow data such as the drawing title to be auto-
matically entered and/or exported from the CAD software. In this case, the title is
not entered directly by the user into the Title Block. Instead, the user is prompted
for this information with a dialog box, and the user enters the information into
fields. Then, the program inserts the field information into the Title Block auto-
matically, and it often makes sure that the character limitations are met by disal-
lowing restricted characters. Also, when data management programs need to
obtain the Title Block information, the programs can then access the title directly
(without having the user view the drawing).

4.5.2 Company Name

The company name is usually found above the drawing title (Figure 4.2). The
address of the company is also often shown in this space. If there is a trademark
logo for the company, it should also be shown. Anything that firmly establishes
the ownership of the trade secret or intellectual property shown in the drawing
should be used. Drawings are still an essential means of establishing ownership
over the design.

4.5.3 Drawing Number

The next item in the Title Block would be the drawing number. This is probably
the most important identifier from a document or design management viewpoint.
Most of the automated data management systems are going to use the drawing
number as the most important or primary “key” for finding and accessing infor-
mation on this drawing or the item it documents (part, assembly, schematic, etc.).

4.5.4 Revision

After the drawing number, probably the next most important information is the
revision or revision level. As seen in Figure 4.2, the revision level is usually to the
right of the drawing number. Often when a drawing is requested the revision level
is included (e.g. a specific image of a drawing may be completely specified by
requesting a number such as 1-111-2-00003 and “Rev” 3).

The revision is often a number or letter that is sequentially increased as the
design documented by the drawing is changed. For instance, the first version of
the drawing released for use could have a revision level of 00, the next version

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would have a level of 01, then 02, etc. However, the change process for a drawing
is not arbitrary; instead, it follows some very important revision or “interchange-
ability” rules. Some changes to a part are substantial enough to warrant a brand
new drawing with a brand new number, instead of just revising the existing draw-
ing. Whether the new number is needed is often dictated by whether the new revi-
sion of the part can be used interchangeably with all previous existing revisions
(that may be in stock).

Another common system for identifying revision level is with letters. In
this case, the initial release of the drawing may show no letter at all. Then the first
revision would be A, the next revision B, etc. Since letters like I and the number 1
look similar, often there are letters that are skipped to prevent confusion.

In conjunction with the revision level, details of the changes made to the
drawing are found in the Revision Block section of the drawing (see Section 4.6).

4.5.5 Predominant Scale

As discussed later in this chapter, drawings represent the physical or geometric
properties of an object using views. These views are drawn to a specified scale. If an
object is 100 mm long and the line drawn in a view to represent that length is drawn
10 mm long, then the scale is 0.1 or 1/10 or 1:10. Usually most or all of the views
on a sheet of the drawing use a given value of scale. The value of this predominant
scale is shown in the Title Block under the heading of SCALE (Figure 4.2).

4.5.6 Weight

It is not unusual for the weight of an object to be a vital piece of information for
the object represented in the drawing (obviously a mechanical drawing in this
case). The standard Title Block includes a space for WEIGHT between the
SCALE and SHEET (Figure 4.2).

4.5.7 Sheet

The standard Title Block includes a space for the sheet or page number (Figure
4.2). If one sheet of a drawing is not enough space to properly document the de-
sign, then additional sheets are created (using the same drawing number and revi-
sion level). This is referred to as a multiple sheet or multisheet drawing. In the
space for SHEET, the sheet number is shown as well as the total number of
sheets. For instance, 1 OF 4 indicates that the sheet is the first of four total sheets
filed under the particular drawing number.

4.5.8 Size

The standard Title Block includes a space for the drawing size. The drawing size
is the letter or number/letter combination for standard drawing sizes discussed
earlier in this chapter. See SIZE in Figure 4.2.

Drawings and 2-D Design 81

4.5.9 CAGE Code

The United States Government has established a numbering system to identify
the type of item or business associated with a manufacturer. At one time this was
known as the FSCM or Federal Supply Code for Manufacturers. More recent
copies of the drawing format standards indicate this number now is the CAGE
Code.

The CAGE Code is a five character (numbers or letters) code. It is shown in
the part of the Title Block under the heading of CAGE. Since this code is often
related to the type of company doing the design or manufacturing (but not the
actual item shown in the drawing), it usually can be set as part of the standard
CAD Title Block just once. Designers or CAD users then do not need to be con-
cerned with it.

4.5.10 Drawer, Checker, Approver

Part of the standard Title Block indicates information about who created the
drawing and how it was checked or approved. This information is found in the
blocks that say DRAWN BY, CHECKED BY, and APPROVED BY.

The DRAWN BY space indicates the person that originally created the
drawing. Along with the name, there is a DATE field to indicate when the draw-
ing was officially created. This is not necessarily as important when CAD sys-
tems control drawings, however. The CAD database and/or operating system
usually also keep date and time information.

Engineering departments may have checkers. These people examine the
drawings before they are released (meaning that other parts of the company
would be looking at them or working from them). When this is done, the name of
the person checking can be shown in the CHECKED BY space. Often, designers
check each other’s work, so just another designer’s name would appear in this
part of the Title Block.

Beyond the checking function, a person in responsible charge (an engineer
or supervisor) approves the drawing. The name of this person along with the date
is shown in the APPROVED BY space.

4.5.11 Additional Approvals

Usually the content of the drawing will be relevant to a specific engineering func-
tion (such as electrical systems, hydraulics, structural integrity, etc.). Often the
performance characteristics of the design needs to be approved. For instance,
electrical schematics need to be functional, and structural components must be
able to withstand expected stresses, etc. This sort of specialized approval is usu-
ally in a separate area of the Title Block (farthest to the left). Space for these
approvals are under the heading of ADDITIONAL APPROVALS. These approv-
als can be vital legal information since the engineer’s name and license number

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may be required for government acceptance of the design for use by the public. In
some cases, having the engineer sign the drawing may still be required, but most
quality systems allow for electronic approvals and/or signatures.

4.6 THE REVISION BLOCK

In addition to the Title Block, a standard drawing format includes a separate sec-
tion of the drawing to indicate revision information. As mentioned earlier, revi-
sions are a very important mechanism for maintaining control over the state of a
design. It is more than just changing something on a drawing; it needs to be coor-
dinated throughout the company and perhaps into the field where the product is
maintained or repaired. It is important for anyone using drawings to know the
revision status of the drawings. The formal process (which should exist) for
changing the design goes by a number of acronyms. Some of these are ECR (En-
gineering Change Record), ECN (Engineering Change Notice), or ECO (Engi-
neering Change Order).

As mentioned earlier, the current revision level of the drawing is indicated
in the Title Block. The Revision Block, then, is used to record some detail of the
“history” of the drawing and the design it is supposed to document. Figure 4.3
shows a typical Revision Block.

The first column of the Revision Block shows the revision level. Obviously
if the drawing is at its first version (say a revision level of 0), there is nothing

FIGURE
4.3

Standard revision block.

Drawings and 2-D Design 83

shown in the Revision Block. But, when the drawing is revised for the first time,
an entry is made in the Revision Block starting with a number 1 in the REV col-
umn. The next revision would then have a row with 2 in the REV column, etc. If
letters are used then REV would show A, B, C, etc. at the start of each row or
entry in the Revision Block.

The second column of the Revision Block shows ZONE, the geographic
region of the drawing that has been modified since the previous revision level.
This is a number and letter combination that indicates a horizontal and vertical
slice of the drawing itself. These numbers and letters are shown in the margin of
the drawing format.

The third column shown for the Revision Block is ECR (Engineering
Change Record), usually a number or character string that is used to track a spe-
cific set of changes to the design. A specific ECR number would be shown in the
Revision Block of all the drawings that were changed “under” that particular
ECR number or process. All these changed drawings together are often referred
to as a package.

The next column of the Revision Block is DESCRIPTION, where the de-
signer or user can place text indicating some detail of the changes made to the
drawing. For instance, “dimension changed value,” or “holes removed from a
plate,” etc. Obviously, there is very limited space for this description, so it needs
to be very concisely written. Some CAD systems allow “memo fields” to be used
for expanded description of the history. These would be stored with the drawing
in the CAD database, but would probably not be shown on a hardcopy of the
drawing itself; it would be printed separately.

The next column in the Revision Block is DATE, when the drawing was
changed, or when the drawing’s ECR was completed and/or released.

The next column in the Revision Block is for INITIALS, the initials of the
person’s name that made the revisions to the drawing.

Finally, the last column in the Revision Block is for APPROVAL. This is
usually the “initials” of the person that is approving the changes to the drawing.

4.7 TYPES OF MECHANICAL DRAWINGS

There are a few basic types of mechanical drawings. Some CAD software may be
better suited to specific types, but in general, they will all handle them to one
degree or another. Table 4.3 lists the types and a basic description. These draw-
ings are shown in an approximation order of “creation” during a design project.
For example, an engineering sketch would often be for preproduction or proto-
types only (i.e. not intended to be manufactured and sold in a final product);
while the word drawing would probably only be needed for actual production
processes.

84 Chapter 4

TABLE
4.3

Basic Types of Mechanical Drawings

Type of drawing Released? Description