True shape and hatching for an inclined section of a cylinder
A cylinder of diameter 60 mm and height 80 mm stands on HP with its axis vertical. A section plane inclined at 45° to HP cuts the cylinder. The plane passes through the axis at a point 40 mm above the base and is perpendicular to VP. The candidate draws a sectional front view in which the cut face is shown as a circle of diameter 60 mm and hatches it with thick lines at 30° to the horizontal. In the top view, the candidate draws the section plane as a thick continuous line across the circle. The candidate labels the circle as the 'true shape'. The drawing uses a 0.7 mm section plane line and 0.3 mm hatching. The candidate asks whether the true shape is a circle or an ellipse and where the hatching should appear.
1. Determine the true shape and its dimensions. Explain why it is not a circle and check that the cut lies within the cylinder height.
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The section plane is inclined at 45° to the cylinder axis (the axis is vertical), so it cuts the cylinder obliquely. The section is an ellipse, not a circle.
Its minor axis is the cylinder diameter, 60 mm, measured across the slope. Its major axis is 60 / cos 45° = 60 / 0.707 = 84.9 mm, measured along the line of greatest slope in the section plane. The plane passes through the axis at 40 mm above the base, so the cut runs from 40 - 30 = 10 mm to 40 + 30 = 70 mm above the base. Both extremes lie within the 80 mm height, so the ellipse is complete. A circle would result only if the plane were perpendicular to the axis; a rectangle would result if it were parallel to the axis.
2. State what the sectional front view and top view should show, and where hatching belongs. Correct the circle and thick-line errors.
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Because the section plane is perpendicular to VP, it appears edge-on as a line in the front view, inclined at 45° to the base line. The sectional front view should show that line and the cut outline, not a circular cut face. In the top view the cylinder still projects as a 60 mm circle; the cut face projects within that circle, and the section plane should not be drawn as a thick continuous line across it.
Hatching belongs only where the cut surface is seen true shape, i.e. in an auxiliary view on a plane parallel to the section plane. There the ellipse is hatched with thin continuous lines at 45° to a reference line, 2-3 mm apart. Do not hatch the front view as if the ellipse were face-on.
3. Correct the section plane line and hatching conventions.
Read the worked answer
Use a chain line with thick ends and two arrows to show the section plane in the view where it appears as a line, and label it A-A. The candidate's 0.7 mm continuous line is the wrong type and weight. Hatching should be thin continuous lines, about 0.25 mm, at 45° to the horizontal or to the centre line, not thick lines at 30°. Hatching on adjacent parts, if any, should slope in opposite directions or be spaced differently. The label 'true shape' belongs on the auxiliary view, not on the 60 mm circle.