Parallel Practices

Parallel Practices Introduction Drawing practices for parallel projections are more standardized than for perspective projections. There is very little latitude for creative interpretation of an object and more use of drawing and drafting instruments. Parallel projections are working drawings or blueprints. Mechanical construction Scale Use a scale, straightedge, triangles, and templates to mechanically construct accurate parallel projections. Select a scale or ratio to represent the object on paper. Modify each measurement you make with the selected scale. Make note of the scale you select to enter in the appropriate space in the title block of the drawing. Layout All elements combined in a parallel projection drawing should present a balanced appearance. If you elect to draw your projection on standard drawing paper with preprinted information blocks and borders, consider the placement of views and the proximity of the information blocks. Make sure the drawing doesn’t overcrowd or interfere with information blocks. Do not arbitrarily alter the relationship of adjacent views on the paper because you incorrectly spaced the views. Measurements All lines parallel to the picture plane project in true size or full scale. All lines perpendicular to the plane of projection project as a point. Oblique or inclined lines are foreshortened. Use offset measurements to locate surface characteristic that share common edges. Circles, arcs, and ellipses Circles, arcs, and ellipses parallel to the plane of projection appear in true size and shape. Circles not parallel to the plane of projection appear as ellipses. Use the system of plotted points or circumscribed circle method of projecting circles, arcs, and ellipses on surfaces not parallel to the plane of projection since these curves have no direct transferable measurements. Reflections, Parallel projections generally do not contain reflections, shadows, and shadows, and shading since this would interfere with any textural implications made by shade crosshatching, stipple, or other pattern. Continued on next page 6-39