Machine Drawing: Orthographic and Sectional Views of Machine Parts
Choosing and arranging views
The front view is chosen to show the characteristic shape of the part; the plan goes below it and the side view beside it, aligned by projection lines, in first-angle. Hidden detail is dashed only where it is needed for clarity and is suppressed where it would clutter the drawing.
Sectional views
A cutting plane marked by a chain line thickened at the ends, with arrows and letters A–A, removes the material between the observer and the plane; the cut surface is hatched with thin continuous lines at 45°, spaced 2–4 mm. Adjacent parts are hatched in opposite directions and the same part is hatched identically in every view. Types: full section; half section for symmetrical parts, one quarter removed so half the view is section and half outside view, divided by a centre line; offset section for features not in one plane; revolved and removed sections for ribs and spokes; broken-out section for a local feature.
Never hatched
Standard bought-out items cut lengthwise - shafts, bolts, nuts, screws, rivets, keys, pins, balls, gear teeth, spokes and thin webs - are drawn in outside view even when the cutting plane passes through them.
Worked example
A symmetrical bearing block with a central bore: take the cutting plane along the centre line. Draw one half of the front view in section, the other half as outside view, the bore appearing as a rectangle with its centre line, the web left unhatched because it is cut lengthwise.
Traps
Hatching a shaft or bolt; showing hidden lines inside a section; hatching two adjacent parts in the same direction; omitting arrows or letters on the cutting plane; splitting a half section along a visible edge instead of the centre line.