1. Chapter Three Drawing Representation:
Sectioning, Welding and Surface Texture

2. Purpose This chapter provides an overview of how to:
apply sectioning techniques to engineering drawings
draw sectional views
represent standard welding data and instructions on drawings
indicate the application of surface texture requirements from machining and other processes on component drawings.

3. Apply sectioning techniques to engineering drawings
3.1 Sectioning—symbols and methods
p.42
Sectional view: part of an object that remains after a portion has been removed.
Reveals interior detail
Only solid material at cutting plane is shown
Typical sectional views for mechanical engineering are illustrated on pp43–47.

4. Apply sectioning techniques to engineering drawings
Hatching lines
The general symbol ‘hatching’ lines are used to indicate face that’s been revealed.
Hatching lines: thin lines normally drawn at 45° (right or left) to the horizontal.
Hatching lines are not to be parallel to sides of object, therefore, another angle may be necessary.
Refer to Figure 3.2, p.42.

5. Apply sectioning techniques to engineering drawings
Adjacent parts
When two parts are adjacent to each other hatching should be at right angles.
Three or more parts may be distinguished by varying the spacing and/or angle of hatching lines. Refer to Figure 3.3(a) and (b), p.42.
Dimensions
Dimensions may be inserted by interrupting the hatching lines. Refer to Figure 3.3(c).

6. Apply sectioning techniques to engineering drawings
Large areas can be shown by hatching around the edges only; see Figure 3.3(d), p.42.
Sectional view and cutting plane
Cutting planes preferably pass through external view and are represented by a thin chain line (type H line); arrowheads indicate the direction of viewing. Refer to Figure 3.4.
Specific cutting plane identified by letters near the tail of the arrow head (e.g. A)
Sectional view identified by letters separated by a hyphen (e.g. section A-A); see Figure 3.7.

7. Apply sectioning techniques to engineering drawings
Hatching thin areas
Thin areas (i.e. gaskets, plastic sheet, packing, sheet metal etc.) when sectioned should be filled in, not hatched. Refer to Figure 3.6(a), p.43.
For two or more adjacent thin areas a small space should be left between the objects. Refer to Figure 3.6(b).

8. Apply sectioning techniques to engineering drawings
Exceptions to the general rules
Webs, shafts, bolts, rivets, keys, pins, rods, balls and similar parts are not sectioned but displayed as a full outline. See Figure 3.7, p.43.

9. Apply sectioning techniques to engineering drawings
Interposed, revolved and removed sections
The cross-section shape of a bar, arm, spoke or rib may be shown as a revolved or interposed section.
Interposed section has detail adjacent to it removed; drawn using a thick line.
Revolved section is a removed cross sectional shape drawn with adjacent detail using thin lines and rotated to show full form. Refer to Figure 3.8, p.43.
Removed sections are similar to revolved, but the cross-section is removed clear of the main outline (Figure 3.9, p.44).

10. Apply sectioning techniques to engineering drawings
To show hidden detail a part or local section may be taken at a suitable location and is drawn freehand (Figure 3.10, p.44).
If the component to be sectioned is not on one plane, the cutting plane may be bent to pass through the relevant detail; however, the section view does not indicate the plane was bent (Figure 3.11(a), p.44).
Note: heavy lines are used to show where the cutting plane changes direction.

11. Apply sectioning techniques to engineering drawings
Holes in circular elements can be rotated to the cutting plane at the true pitch distance from centre. Refer to Figure 3.11(a), p.44.

12. Draw sectional views
Sectional views are included in normal orthogonal drawings to show internal detail otherwise only represented by hidden detail
Figure 3.13
Figure 3.12

13. Draw sectional views
Full sectional views are basically the component cut in half (down the middle) along the cutting plane (see Figure 3.13).
Offset sectional views show interior detail which lies along two or more planes. Refer to Figures and 3.15, p.46.
Half sectional views effectively remove a quarter of an object (generally symmetrical about a centre line). Hidden detail may be included in quarter not sectioned (see Figures 3.16 and 3.17).

14. Rules to remember when sectioning.
A sectional view shows the part of the component in front of the cutting plane arrows. In third angle projection the sectional view is placed on the side behind the sectioning viewing plane.
Material which has been cut by the cutting plane is hatched with some standard exceptions.
A sectional view must not have any full lines drawn over hatched areas.
Generally, hatched areas are not dimensioned unless unavoidable.

15. Welding drafting and standards
Refer to AS1100 (Graphic symbols for general engineering) Part 3 for in-depth information.
Figure 3.18

16. Welding drafting and standards
‘Weld symbol’ indicates type of weld only.
‘Welding symbol’ is a complete instruction indicating the particular joint, type of weld and supplementary instructions necessary to complete the weld. Refer to Table 3.1 Basic symbols for welding and Figure 3.18 Standard location of elements on a welding symbol, pp.47–48.

17. The standard welding symbol
Standard welding symbol (see Figure 3.18)
Arrow inclined between 30 to 90 degrees which points to weld in either direction.
Horizontal reference line 20 to 30mm long.
Tail for supplementary information when required.
A basic weld symbol is located in centre position of the reference line, either above, below or both (Table 3.1).
Supplementary symbols are positioned around the symbol in certain positions.

18. Welding drafting
Reference to Tables 3.1, 3.2 and 3.5 (pp.48–50) and the letter designation table of welding processes (Table 3.3, pp.51–52) will assist in drawing the required welding symbol.
Figure 3.19, p.49, illustrates the standard terminology for various elements of fillet and butt welds.

19. Welding drafting
Where possible the arrow should be positioned adjacent to the weld, with the symbol underneath the reference line, indicating a weld at the arrow.
Where a weld side is not accessible due to other detail, the symbol is placed on top of the reference line, indicating the weld is on the other side of the feature.

20. Welding drafting
Supplementary information (e.g. Table 3.3) is included at a tail added to the reference line (see Figure 3.18) and positioned where indicated.
A procedure sheet may be added to the drawing itemising production information such as type of material, form of weld, set up details, number of runs, electrode size/type, electrical supply, preheating requirements, pre- and post treatments, and any other relevant detail deemed necessary.

21. Welding drafting
The arrow is cranked as shown in Figure 3.21, p.50, and points to the plate, indicating which plate has to be prepared for welding a single bevel or single—J butt joint.
The crank can be omitted when the edge to be prepared is obvious.

22. Surface texture
Surface finish specifications (finish, production methods and/or roughness of surface) can be identified on a drawing when required.
Surface roughness measurement ( ) is the average difference between the peaks and troughs to a centre line over a sampling length. Refer to Figure 3.23, p.53.
A roughness symbol should only be used once for a given surface.

23. Surface texture
Surface finish symbols have a basic shape which may have further information attached to it.
Figure 3.24(a) illustrates the basic symbol.
Figure 3.24(b) illustrates a basic symbol with a bar indicating a machined flat finish.
Figure 3.24(c) illustrates a basic symbol with a circle indicating removal of material is not permitted.
Figure 3.24(d) illustrates type of information that may be included.

24. Surface texture
Table 3.8, p.57 lists the various roughness values ( ) and processes used to produce them.
Table 3.9, p.58 provides a more detailed specification of the roughness range applicable to various production processes.

25. Surface texture
The symbol should be able to be read from the bottom or right-hand side of the drawing.
Should be applied to the edge of the surface in question.
Extension and leader lines may be incorporated.
Fig 3.25, p.54 illustrates correct methods for applying.
Where necessary roughness grade numbers may be used instead of value. Refer to Table 3.6, p.54.

26. Direction of surface pattern or lay
Table 3.10, p.58, illustrates the standard symbols for various lay directions resulting from different production processes.

27. Representation of common features.
Table 3.11, p.59, shows typical examples of features which would normally involve unnecessary drawing time and space.
Table 3.12, p.62, illustrates bolts, nuts and screws and the convention for drawing them.

28. Summary
To create a section view, the cutting plane must be identified by use of a thin chain line, preferably with arrow heads identifying the direction for viewing. Sectional views can be full, aligned, partial, offset and half, and are identified by hatching lines.
When drawings include welded features, this entails the use of welding symbols and/or a procedure sheet to identify all relevant requirements for the weld process.

29. Summary
Operational surfaces often require a specific surface finish, indicated on the drawing by the surface finish symbol; information on the symbol may include all necessary tasks to achieve the final finish.
To reduce drawing time, common features are represented by a drawing convention simplifying their appearance.