Understanding Industrial Blueprints 175
A casting drawing details the size and location of separation lines, called parting lines. When the
mold separates, the parting line is left on the casting. The other information typically found on a casting
detail drawing may be a pattern number, sand requirements, part numbers, customer name, draft,
shrinkage, finish, ribs and other support webbing, and the material used in the casting/mold.
Wood patterns, made by patternmakers in the general male or female shape of the finished part are
configured into the sand mold and removed, leaving an impression to be filled with molten metal. When
cooled, this metal casting is removed and the process is continued. These castings are then machined
into items such as engine blocks, cast-iron tools, or other metal castings we use every day. Bearing
blocks, machinery bases and parts, and many household items have castings produced in this manner.
7.3 MACHINIST DRAWINGS.
Machinists generally use precision machine tools such as lathes, boring machines, milling machines,
and cylindrical or surface grinders to shape materials such as steel, brass, iron, bronze, aluminum, tita-
nium, and plastics and to manufacture components to meet customers’ specifications.
A machining detail drawing provides all the information needed to manufacture a specific part and
is used to machine the casting into a finished component. Typically only one part is detailed in each
drawing. Machining details are generally used when machining a rough part into a finished part; a ma-
chining detail drawing will specify the surfaces to be machined, bolt holes and locations, reference
points, geometric dimensioning and tolerancing (GD & T), and other machined areas. Machining draw-
ings contain critical information to the traditional or CNC (computer numerically controlled) machinist,
which would include angles, reference points, surface finish, etc. Once complete, this machined part
should match and fit other machined parts as defined in an assembly/detail drawing. Parts that would
not normally need to be drawn are standard parts—those that may be purchased from an external
source more economically than it would cost to manufacture. Such parts may include screws, nuts, bolts,
keys, and pins. While they do not need to be drawn, they nevertheless need to be included as part of
the information on each sheet. The blueprint reader must clearly understand the shape, size, material,
and surface finish of a part, which shop operations are necessary, and the limits of accuracy that must
be observed from the detail drawing. Figure 7.12 is an example of a typical detail drawing.
Normally, detail drawings contain information that is classifiable into three groups:
- Shape description: describes and explains or portrays the shape of the component
- Size depiction: shows the size and location of features of the component
- Specifications: relates to such items as material and finish
Detail machine drawings should include all or most of the following information:- Views of the component as necessary to allow visualization
- Material used to manufacture the component
- Dimensions
- General notes and specific manufacturing information
- Identification of the project name, the part, and the part number
- Name or initials of who worked on or with the drawing
- Any engineering changes and related information