Drawing – CAD Standards
Drawings standards help Industrial Designers and Engineers create a seamless transition from design to prototype to manufacturing. These standards include unit scale and size of drawings, views, dimensioning (measurements) and tolerances. Typically drawing plans are either hand drawn with drawing guides or they are produced in a computer program and printed on paper. Import and export formatting standards (PDF, DXF, DWG) help communicate a design and enough information to allow a manufacturer to build or fabricate shape, cast or mold the product. With 3D CAD files there is no misinterpretation of the drawings or design intent; you get what you deliver. All dimensioning and tolerancing should be arranged for maximum readability and should be applied to visible lines in true profiles.
See ID Design Control Drawings and ME Engineering CAD Drawings
Multiple views and projections
In most cases, a single view is not sufficient to show all necessary features, and several views are used. Types of views include the following:
Orthographic Projection – show the object as it looks from the front, right, left, top, bottom, or back, and are typically positioned relative to each other according to the rules of either first-angle or third-angle projection.
Detail – show portions of other views, “magnified” for clarity.
Auxiliary projection – similar to orthographic projections, however the directions of viewing are other than those for orthographic projections.
Isometric – show the object from angles in which the scales along each axis of the object are equal (no vanishing points). It corresponds to rotation of the object by ± 45° about the vertical axis, followed by rotation of approximately ± 35.264° [= arcsin(tan(30°))] about the horizontal axis starting from an orthographic projection view. “Isometric” comes from the Greek for “same measure.”
All dimensions must have a tolerance. Every feature on every manufactured part is subject to variation, therefore, the limits of allowable variation must be specified. Plus and minus tolerances may be applied directly to dimensions or applied from a general tolerance block or general note. Dimensioning and tolerancing shall completely define the nominal geometry and allowable variation. Note that as tolerances get smaller (this means that the allowed variation from the specified dimension is smaller), manufacturing costs generally go up.
Orthographic projection views
Orthographic projection is a means of drawing a three-dimensional (3D) object in two dimensions (2D). It is a form of parallel projection, where the view direction is orthogonal to the projection plane. It is further divided into multi-view orthographic projections and axonometric projections. With multi-view orthographic projections, up to six pictures of an object are produced, with the projection plane parallel to one of the coordinate axes of the object WD uses the Cartesian axes (x, y, and z) for defining the ground and sky or length, width and height.
The views are positioned relative to each other according to XYZ axes in either of two schemes: first-angle or third-angle projection. In each, the appearances of views may be thought of as being projected onto planes that form a 6-sided box around the object.
Perspective is an approximate representation, on a flat surface (such as paper), of an image as it is perceived by the eye. Objects drawn in perspective becomer smaller as their distance from the observer increases. As the distance from the viewer increases, lines in the drawing converge at a “vanishing point.” Perspective drawings can utilize three, two, or (rarely) one vanishing point.
As part of the 3D CAD Model assembly ther use of an exploded part assembly is typically an isometric projections. The view typically provides a referenced numbered list of all the primary parts and 2D drawings including a Bill of Materials or (BOM) which will include part quantites, materials, manufacturing processes and finish requirements.