SECTION OF SOLIDS CLASS NOTES
Section of solids provides inner details of
an object. Section of solids is essential for
objects whose inside and outside are
different. Section views are a very
important for designing an object or a
machine. Section of solids improve clarity
and reveal interior features of parts which
are other wise not visible. Sections of
solids are based on the use of an imaginary
cutting plane to reveal the interior details.
Its importance is much more for
complicated assemblies. Hidden edges as dotted lines are
not shown in the sectional views.
Q 1 What do you mean by section (cutting) of a solid?
Many solids have different external and internal construction. Normally external surfaces are projected. Solid is cut to project the internal constructional details. This cutting of the solid to know the internal details is section of solids. Views drawn after sectioning are sectional views. Section lines at 450 to the ground line show the cut surface of the solid. The distance between the section lines is constant. Draw sectional views of a prism, pyramid & cylinder.
Q 2 What is a section plane or a cutting plane?
Cutting plane cuts the solid to know the internal constructional details. This cutting plane is perpendicular/ parallel/ inclined to one of the principle planes of projections. These section planes are represented by their Horizontal (H.T.) & Vertical traces (V.T.).
(i) First section plane perpendicular to VP and parallel to HP. Its VT is parallel to xy.
(ii) Second section plane perpendicular to HP and parallel to VP. Its HT is parallel to xy.
(iii) Third section plane perpendicular to VP and inclined to HP. Its VT is inclined to xy and is above xy.
(iv)Fourth section plane perpendicular to HP and inclined to VP. Its HT is inclined to xy and is below xy.
Q 3 What do you understand by H.T. and V.T. of a section plane?
Horizontal trace (H.T) – H.T. of a section plane is a line in which the section plane meets the H.P.
Vertical trace (V.T.) – V.T. of a section plane is a line in which the section plane meets the V.P.
Q 4 What are section lines or hatching lines?
Section lines are the equidistant parallel lines representing the material cut by the cutting plane. These are hatching lines. These are equally spaced lines inclined at 45 º to the horizontal & vertical. Complicated solids use more than one section plane to draw the complete details. Different equally spaced lines represent the different cut portions. Same cutting plane cuts a solid made of more than one material. One set of section lines at constant distance represent one material. While another set of section lines represent the other material.
Q 5 What is a sectional view? Why sectional views used in drawing?
The view obtained from the cut portion the object is the sectional view. There can be sectional top view, sectional front view, sectional side view.
Q 6 What is apparent section?
The projection on an inclined plane of the left portion is the apparent section. Thus, apparent section is smaller than the true size of portion cut.
Q 7 What is true section?
The projection on a parallel plane of the left portion is the true section. True section is of same size as the portion after actual cut.
Q 8 What are the different types of sections of solids?
Different positions of the section planes are as under:
1) Section of solids by a horizontal plane parallel to HP.
2) Section of solids by a vertical plane parallel to VP.
3) Section of solids by an auxiliary inclined plane (AIP).
4) Section of solids by an auxiliary vertical planes (VIP).
5) Section of solids by a profile plane
Q 9 What do you mean by Frustum?
The cutting plane is parallel to the base of a prism, pyramid or cone. Remove the portion between the observer and the cutting plane. Remaining portion is Frustum of a solid.
Q 10 What do you mean by truncated?
Section the solid with a section plane inclined to the base of a solid. Remove the portion between the observer and the cutting plane. Remaining portion is the truncated solid.
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