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Drawings

Drawings or sketches are used to convey the ideas of an engineer to the skilled craftsman working in the shop. As a welder, you must be able to work from a drawing in order to fabricate metal parts exactly as the engineer has designed them.

READING DRAWINGS

To read a drawing, you must know how engineers use lines, dimensions, and notes to communicate their ideas on paper. In this section, we briefly discuss each of these drawing elements.

Lines

Figure 3-38 shows many of the different types of lines that are used in drawings. You can see that each line has a specific meaning you must understand to interpret a drawing correctly. Let’s discuss a few of the most important types. A visible line (sometimes called object line) is used to show the edges of an object that are visible to the viewer. For example, if you look at one of the walls of the room you are in, you can see the outline of the walls and (depending on the wall you are looking at) the outline of doors and windows. On a drawing, these visible outlines or edges can be shown using visible lines that are drawn as described in figure 3-38.

Now look at the wall again. Assuming that the wall is wood frame, you know that there are studs or framing members inside the wall that you cannot see. Also, the wall may contain other items, such as water pipes and electrical conduit, that you also cannot see. On a drawing, the edges of those concealed studs and other items can be shown using hidden lines (fig.3-38). These lines are commonly used in drawings. As you can imagine, the more hidden lines there are, the more difficult it becomes to decipher what is what; however, there is another way these studs and other items can be “seen.” Imagine that you “cut away” the wallboard that covers the wall and replace it with a sheet of clear plastic. That clear plastic can be thought of as a cutting or viewing plane (fig.3-38) through which the previously concealed studs, piping, and conduit are now visible. Now those items can be drawn using visible lines, rather than hidden lines. A view of this type is called a sectional view, and a drawing of the view is called a section drawing. Section drawings are commonly used to show the internal components of a complicated object.

Many times, you will see lines drawn on the visible surfaces of a section drawing. These lines, called section lines, are used to show different types of materials. .Some of the types of section lines you are likely to encounter as a welder are shown in figure 3-39.

Another use of lines is to form symbols, such as welding symbols, that are discussed later in this chapter.

Dimensions

While engineers use lines to describe the shape or form of an object, they use dimensions to provide a complete size description. Dimensions used on draw-ings are of two types: size and location. As implied by their names, a size dimension shows the size of an object or parts of an object and a location dimension is used to describe the location of features. Examples of both size and location dimensions are shown in figure 3-40. While on the subject of dimensions, it should be noted that large objects are seldom drawn to their true size. Instead, the engineer or draftsman reduces the size of the object “to scale.” For example, when drawing a 40-foot tower, the drawing may be prepared using a scale of 1/2"= 1'-0". In this case, the height of the tower, on paper, is 20 inches. The scale used to prepare working drawings is always noted on the drawing. It maybe a fractional scale, such as discussed here, or a graphic scale, such as the one shown in figure 3-40. Often both numerical and graphic scales are usually shown on construction drawings.

When you are using a drawing, the dimensions of an object should never be measured (scaled) directly from the drawing. These measurements are frequently inaccurate, since a change in atmospheric conditions causes drawing paper to shrink or expand. To ensure accuracy, always use the size and location dimensions shown on the drawing. If a needed dimension is not shown on the drawing, you should check the graphic scale, since it will always shrink or expand at the same rate as the drawing paper.

Notes
Drawing notes are used for different purposes and are either general or specific in nature. One example of how notes are used are the two notes shown in figure 3-40 that give the inside diameters of the holes. As you can see, these notes are used for size dimensioning. They are specific notes in that, by using a leader line, each note is referred to a specific hole or set of holes.

A general note is used to provide additional infor-mation that does not apply to any one particular part or feature of the drawing. For example, the drawing shown in figure 3-40 could contain a general note saying: “All holes shall be reamed using a tolerance of ± 1/64 inch.”

Drawing Views

Look at the drawing shown in figure 3-41. This type of drawing is called a pictorial drawing. These draw-ings are frequently used to show how an object should appear after it is manufactured. Pictorial drawings are used as working drawings for a simple item, such as a metal washer. For a more complex object, as shown in figure 3-41, it becomes too difficult to provide a com-plete description in a pictorial drawing. In this case, it is common practice to prepare orthographic drawings to describe the object fully. Assume you are holding the object shown in figure 3-41 in your hands. When you hold the object so you are looking directly at the top face of the object, the view you see is the top view. A drawing of that view is called an orthographic drawing.

Obviously, an orthographic drawing of only the top view of the object is insufficient to describe the entire object; therefore, additional orthographic drawings of one or more of the other faces of the object are necessary. The number of orthographic views needed to describe an object fully depends upon the complexity of the object. For example, a simple metal washer can be fully described using only one orthographic view; however, an extremely complex object may require as many as six views (top, front, left side, right side, back, and bottom). Most objects, such as the steel part shown in figure 3-41, can be sufficiently described using three views: top, front, and right side. For the object shown in figure 3-41, orthographic drawings of the top, front, and right-side views are shown in figure 3-42. Notice the placement of the views shown in figure 3-42. This is a standard practice that you should be aware of when reading orthographic drawings. By this standard practice, the top view is always placed above the front view and the right-side view is placed to the right of the front view. When additional views are needed, the left side is always drawn to the left of the front view and the bottom is drawn below the front view. Placement of the back view is somewhat flexible; how-ever, it is usually drawn to the left of the left-side view. When reading and understanding the different orthographic views, you find it is sometimes helpful to prepare a pictorial sketch.

Think of drawings as a form of communication. They are intended to help you understand all the necessary information you need to fabricate and assemble an object regardless of the complexity. It is important that you learn to read drawings.

Handling and Care of Drawings
Special care should be exercised in the handling of drawings. When they are not being used, keep them on a rack or in another assigned place of storage. Drawings are valuable, and they may be difficult or impossible to replace if they are lost or damaged.

Now, we will discuss some special symbols. These are symbols a welder must be able to read and to understand how they are used to convey information.

WELDING SYMBOLS

Special symbols are used on a drawing to specify where welds are to be located, the type of joint to be used, as well as the size and amount of weld metal to be deposited in the joint. These symbols have been standardized by the American Welding Society (AWS). You will come into contact with these symbols anytime you do a welding job from a set of blueprints. You need to have a working knowledge of the basic weld symbols and the standard location of all the elements of a welding symbol.

A standard welding symbol (fig. 3-43) consists of a reference line, an arrow, and a tail. The reference line becomes the foundation of the welding symbol. It is used to apply weld symbols, dimensions, and other data to the weld. The arrow simply connects the reference line to the joint or area to be welded. The direction of the arrow has no bearing on the significance of the reference line. The tail of the welding symbol is used only when necessary to include a specification, process, or other reference information.

Weld Symbols

The term weld symbol refers to the symbol for a specific type of weld. As discussed earlier, fillet, groove, surfacing, plug, and slot are all types of welds. Basic weld symbols are shown in figure 3-44. The weld symbol is only part of the information required in the welding symbol. The term welding symbol refers to the total symbol, which includes all information needed to specify the weld(s) required.

Figure 3-45 shows how a weld symbol is applied to the reference line. Notice that the vertical leg of the weld symbol is shown drawn to the left of the slanted leg. Regardless of whether the symbol is for a fillet, bevel, J-groove, or flare-bevel weld, the vertical leg is always drawn to the left.

Figure 3-46 shows the significance of the positions of the weld symbols position on the reference line. In view A the weld symbol is on the lower side of the reference line that is termed the arrow side. View B shows a weld symbol on the upper side of the reference line that is termed the other side. When weld symbols are placed on both sides of the reference line, welds must be made on both sides of the joint (view C).

When only one edge of a joint is to be beveled, it is necessary to show which member is to be beveled. When such a joint is specified, the arrow of the welding symbol points with a definite break toward the member to be beveled. This is shown in figure 3-47.

Figure 3-48 shows other elements that may be added to a welding symbol. The information applied to the reference line on a welding symbol is read from left to right regardless of the direction of the arrow.

Dimensioning
In figure 3-48, notice there are designated locations for the size, length, pitch (center-to-center spacing), groove angle, and root opening of a weld. These locations are determined by the side of the reference line on which the weld symbol is placed. Figure 3-49 shows how dimensions are applied to symbols.

Figure 3-50 shows the meaning of various welding dimension symbols. Notice that the size of a weld is shown on the left side of the weld symbol (fig. 3-50, view A). The length and pitch of a fillet weld are indicated on the right side of the weld symbol. View B shows a tee joint with 2-inch intermittent fillet welds that are 5 inches apart, on center. The size of a groove weld is shown in view C. Both sides are 1/2 inch, but note that the 60-degree groove is on the other side of the joint and the 45-degree groove is on the arrow side.

Supplementary Symbols

In addition to basic weld symbols, a set of supplementary symbols may be added to a welding symbol. Some of the most common supplementary symbols are shown in figure 3-51.

Contour symbols are used with weld symbols to show how the face of the weld is to be formed. In addition to contour symbols, finish symbols are used to indicate the method to use for forming the contour of the weld.

When a finish symbol is used, it shows the method of finish, not the degree of finish; for example, a C is used to indicate finish by chipping, an M means machining, and a G indicates grinding. Figure 3-52 shows how contour and finish symbols are applied to a weldng symbol. This figure shows that the weld is to be ground flush. Also, notice that the symbols are placed on the same side of the reference line as the weld symbol.

Another supplementary symbol shown in figure 3-51 is the weld-all-around symbol. When this symbol is placed on a welding symbol, welds are to continue all around the joint.

Welds that cannot be made in the shop are identified as field welds. A field weld symbol is shown in figure 3-51. This symbol is a black flag that points toward the tail of the welding symbol.

Specifying Additional Information

It is sometimes necessary to specify a certain welding process, a type of electrode, or some type of reference necessary to complete a weld. In this case, a note can be placed in the tail of the reference line. (See fig. 3-53.) If additional information is not needed, then the tail is omitted.

Multiple-Weld Symbols

When you are fabricating a metal part, there are times when more than one type of weld is needed on the same joint; for example, a joint may require both a bevel groove weld and a fillet weld. Two methods of illustrating these weld symbols are shown in figure 3-54. Note that in each welding symbol, the bevel groove weld is to be completed first, followed by the fillet weld.

Applying a Welding Symbol

Figure 3-55 shows an example of how a welding symbol may appear on a drawing. This figure shows a steel pipe column that is to be welded to a baseplate. The symbol tells the welder that the pipe is to be beveled at a 30-degree angle followed by a bevel groove weld all around the joint. This is followed by a 1/2-inch fillet weld that is also welded all around the joint. Finally, finish the fillet weld by grinding it to a flush contour. As the field weld symbol indicates, all welds are to be accomplished in the field.

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