PREPARATION OF A BILL OF MATERIALS

The designer/drafter is usually required to prepare a list or bill of materials along with weldment drawings. This list enables some other person, such as a stockroom attendant, a welder’s helper, or the operator of flame - cutting equipment, to cut or otherwise prepare the various stock pieces needed to fabricate the object.

In many cases, the bill of materials is simply a list of dimensions and the number of pieces required. For complex or irregularly shaped objects, sketches may be added to fully describe certain parts.

To prepare the bill of materials, each part must be considered individually. All pertinent information, such as part name or number, number of pieces required, thickness, width, length, and kind of material, should be listed for each part.

A bill of materials is shown directly on detail and subassembly drawings within a ruled block, or on a separate sheet attached to the drawing. Figure 5.1 illustrates two examples of ruled blocks found on drawings

Bill of Materials

No.	Material	Size

for inclusion of bill of materials information. Note that a ruled block for this purpose is in addition to the title block, which provides other kinds of information.

10 - 1/4" X З" X 8" t— LENGTH I— WIDTH — THICKNESS - NUMBER REQUIRED

The sizes of a part for a bill of materials are expressed in a particular order as illus­trated by the following example. Assume that a T-joint is to be fabricated from two plates. Consider one plate at a time and list the number required and the thickness, width, and length of each. Figure 5.2 shows that 10 pieces are required. The bottom part is thick, 3" wide, and 8" long. This information is written as:

ITEM	PART NO.	QTY,	DESCRIPTION

FIGURE 5.1 ■ Examples of ruled blocks for bill of materials.

Ten pieces of the upright part (B are also required. This part is thick, 21i4 " wide, and 8" long and is specified as:

FIGURE 5.2 ■ T-joint.

10 - 1/2И X 21/4n X 8й

L

LENGTH I— WIDTH THICKNESS NUMBER REQUIRED

The basic bill of materials for the T-joint is:

FIGURE 5.3 ■ Cutting material from plate.

Additional information can be included in the bill of materials to reduce the likelihood of any mis­understanding. For example, the list of materials for Figure 5.2 gives no indication as to whether the parts are to be cut from sheet, plate, or flat bar. Sheet metal is defined as metal 3/іб" or less in thickness and more than 6" in width. Metal plate is greater than 33ie" in thickness, and also is more than 6" in width. Both plate and sheet are available in widths up to 200 inches and lengths of up to 100 feet. Flat bar stock differs from plate and sheet in that the width of the bar does not exceed 6". Many thicknesses are available, and the length may vary from 18 to 22 feet. Note that the kind of material to be used (i. e., SAE 1020 steel, aluminum, copper, etc.) will also need to be specified when of a special nature.

Since Figure 5.2 does not indicate the stock to be used, it can be assumed that it makes little differ­ence from which stock form the parts are cut. How­ever, if the parts required are to be cut from plate, Figure 5.3, the bill of materials is written as:

If the parts required are to be cut from flat bar, Figure 5.4, the material requirement is written as:

10 - 1 /4" x 3й x 8" LONG 10 - У 2" x 21А" x 8'' LONG

LENGTH

Note that the word long is used and the X sign between the width and length dimensions is not used.

In some cases the word flat is used following the width dimension to reduce any possibility of a misunderstanding:

10 - 14" X 3'' FLAT 8'' LONG 10 - 12'' X 214'' FLAT 8'' LONG

If the flat stock is of the required width and thick­ness, then parts need only be cut to the required length.

Figure 5.5 illustrates a typical detail assembly drawing from which a bill of materials can be pre­pared. Sufficient information in terms of sizes and kinds of material is shown on the drawing.

The examples cited thus far are representative of bills of materials for simple objects. Other objects may be more complex and may involve circumference calculations, or may be concerned with diameter or radius dimensions rather than lengths or widths. Examples of calculations that may be required in the preparation of a bill of materials are illustrated in Figure 5.6.

FIGURE 5.5 ■ Complete listing of materials shown on a drawing.

As the outside diameter (OD) is given and centerlines: are shown, it is clearly indi­cated that this is a circular plate and, since the inside diameter (ID) is given, it is obvious that there is a hole in the circular plate (Part A).

1 -3/4" PL30'' OD 24" ID

P^ 42 1/4” x 77"

This dimension is calcu­lated using the mean diameter between the ID and the OD. In this case, the mean diam­eter is 24 1/2" (25 + 24 - r 2). The formula used is 24 1/2" x 22/7 = 77". Note: Use 3.14 for decimal dimensions.

ORDER NO-—_________ - NAME OF PART________ NUMSER REQUIRED-

FIGURE 5.6 ■ Calculating sizes for a bill of materials.

(PART A)

- 1/2'

(PART B)

16 GA SHEET J / 3 x3-, L _ ANGLE I