In order to show the inner details of a machine component, the object is imagined to be cut by a cutting plane and the section is viewed after the removal of cut portion. Sections are made by at cutting planes and are designated by capital letters and the direction of viewing is indicated by arrow marks.
Hatching of Sections
Hatching is generally used to show areas of sections. The simplest form of hatching is generally adequate for the purpose, and may be continuous thin lines (type B) at a convenient angle, preferably 45°, to the principal outlines or lines of symmetry of the sections.
Separate areas of a section of the same component shall be hatched in an identical manner. The hatching of adjacent components shall be carried out with different directions or spacings (a). In case of large areas, the hatching may be limited to a zone, following the contour of the hatched area (b).
Where sections of the same part in parallel planes are shown side by side, the hatching shall be identical, but may be off-set along the dividing line between the sections (Sectioning along two parallel planes). Hatching should be interrupted when it is not possible to place inscriptions outside the hatched area (Hatching interrupted for dimensioning).
The cutting plane(s) should be indicated by means of type H line. The cutting plane should be identified by capital letters and the direction of viewing should be indicated by arrows. The section should be indicated by the relevant designation.
In principle, ribs, fasteners, shafts, spokes of wheels and the like are not cut in longitudinal sections and therefore should not be hatched.
Figure (a) represents sectioning in two parallel planes and Fig. (b) that of sectioning in three continuous planes.
Sectioning in two intersecting planes, in which one is shown revolved into plane of projection, as shown in Fig. (a).
In case of parts of revolution, containing regularly spaced details that require to be shown in section, but are not situated in the cutting plane; such details may be depicted by rotating them into the cutting plane (Fig. (b)).
Revolved or Removed Section
Cross sections may be revolved in the relevant view or removed. When revolved in the relevant view, the outline of the section should be shown with continuous thin lines (Revolved section figure). When removed, the outline of the section should be drawn with continuous thick lines. The removed section may be placed near to and connected with the view by a chain thin line (Fig. Removed section a) or in a different position and identified in the conventional manner, as shown in Fig. Removed section b.
Symmetrical parts may be drawn, half in plain view and half in section.
A local section may be drawn if half or full section is not convenient. The local break may be shown by a continuous thin free hand line.
Arrangement of Successive Sections
Successive sections may be placed separately, with designations for both cutting planes and sections or may be arranged below the cutting planes.