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In the piping discipline a north arrow is used as a “point of reference.” Accurate isometric layout is based on the correlation of the orientation of the north arrow on the Piping Arrangement drawing and the north arrow on the piping isometric. The complexity of piping configurations requires a more descriptive “point of reference” be used to establish orientation between the orthographic and isometric views. Although the A can be seen in Figures 13.3 and 13.4, it is not an adequate point of reference.

Similarly, on piping isometrics, establishing a point of reference is imperative. By using a point of reference, proper orientation of the isometric can occur by transferring distance and direction from the orthographic view.

Dimensions are placed on an isometric sectional view in the same way they are for regular isometric drawings.Note in Figures 13.1 and 13.2 how the height, width, and depth dimensions of the L-shaped object in the orthographic views are oriented on the isometric view with A as a point of reference. Isometric sectional views do not require a defining cutting plane and are usually presented as individual pictures with no accompanying reference drawing. Note that, as with orthographic sectional views, hidden lines are omitted and the cross-hatching lines are drawn medium to light in color, 3/32 apart at an inclined angle. Figure 54 shows a full isometric sectional view and a half isometric sectional view. Isometric sectional views are used for the same reasons that orthographic sectional views are used, to clarify objects by exposing important internal surfaces that would otherwise be hidden from direct view. The numbers are drawn either 1/8 or 3/16 inch in height in both systems.į. Figure 53 (on the previous page) is another example of the unidirectional system.

The guidelines for the dimensions in the aligned system are drawn parallel to the edge being defined, while the guidelines for the unidirectional system are always horizontal. Regardless of the system used, the leader lines must be drawn in the same isometric plane as the surface they are defining. Isometric drawings may be dimensioned by using either the aligned system or the unidirectional system.