2D DRAWING REPRESENTATION C H A P T E R S I X

OBJECTIVES 1. Represent curved surfaces in multiview drawings 2. Show intersections and tangencies of curved and planar surfaces 3. Represent common types of holes 4. Show fillets, rounds, and runouts in a 2D drawing 5. Use partial views 6. Apply revolution conventions when necessary for clarity 7. Draw removed views and projected views 8. Show right- and left-hand parts 9. Project curved surfaces by points 10. Show and label an enlarged detail 11. Show conventional breaks

Common Manufactured Features Fillet Round Counterbore Countersink Spotface Boss Lug Flange Chamfer Neck Keyway/Keyseat Knurl Bushing

Conventional Representations Standard orthographic projections don’t always show complex shapes as clearly and simply as you may wish, so certain alternative practices, referred to as conventions, are accepted. Conventions are like rules for breaking the rules. Note how these views are projected Orthographic Views of Intersecting and Tangent Surfaces. (Lockhart, Shawna D.; Johnson, Cindy M., Engineering Design Communication: Conveying DesignThrough Graphics, 1st, © 2000. Printed and Electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey.)

VISUALIZING AND DRAWING COMPLEX CYLINDRICAL SHAPES Steps

CYLINDERS WHEN SLICED Cylinders are often machined to form plane or other types of surfaces. Normal surfaces appear true shape in the view where the line of sight is perpendicular to the surface. In the two other views that normal surface appears on edge. The back half remains unchanged.

CYLINDERS AND ELLIPSES If a cylinder is cut by an inclined plane, the inclined surface is bounded by an ellipse. This ellipse will appear as a circle in the top view, as a straight line in the front view, and as an ellipse in the side view. When a circular shape is shown inclined in another view and projected into the adjacent view it will appear as an ellipse, even though the shape is a circle.

INTERSECTIONS AND TANGENCIES Where a curved surface is tangent to a plane surface no line is drawn, but when it intersects a plane surface, a definite edge is formed. When plane surfaces join a contoured surface, a line is shown if they are tangent, but not shown if they intersect.

Intersections of Cylinders When the intersection is small, its curved shape is not plotted accurately because it adds little to the sketch or drawing for the time it takes. Instead it is shown as a straight line. When the intersection is larger, it can be approximated by drawing an arc with the radius the same as that of the large cylinder.

FILLETS AND ROUNDS A rounded interior corner is called a fillet. A rounded exterior corner is called a round. Rounds on a CAD Model of a Design for a Three-Hole Punch Fillets on a CAD Model. (Courtesy of Douglas Wintin.) (Courtesy of Ross Traeholt.)

RUNOUTS Small curves called runouts are used to represent fillets that connect with plane surfaces tangent to cylinders. Runouts from different filleted intersections will appear different owing to the shapes of the horizontal intersecting members.

CONVENTIONAL EDGES There is a conventional way of showing rounded and filleted edges for the sake of clarity. Added lines depicting rounded and filleted edges. Rounded and filleted intersections eliminate sharp edges and can make it difficult to present the shape clearly.

NECESSARY VIEWS What are the absolute minimum views required to completely define an object? One-View Drawing Two-View Drawing Three-View Drawing

PARTIAL VIEWS You can use a break line to limit the partial view… A view may not need to be complete but needs to show what is necessary to clearly describe the object. This is called a partial view and is used to save sketching time and make the drawing less confusing to read. OR You can use a break line to limit the partial view…

Showing Enlarged Details When adding a detail, draw a circle around the features that will be included in the detail Place the detail view on the sheet as you would a removed view. Label successive details with the word DETAIL followed by a letter, as in DETAILA, DETAIL B,

Conventional Breaks To shorten the view of a long object, you can use break lines… Using a break to leave out a portion of the part, but allows the scale for the ends to be increased to show the details clearly.

ALIGNMENT OF VIEWS Always draw views in the “standard” arrangement... Because CAD makes it easy to move whole views, it is tempting to place views where they fit on the screen or plotted sheet and not in the standard arrangement. This is not acceptable. 3D CAD software that generates 2D drawing views as projections of the 3D object usually has a setting to select from third-angle or first-angle projection. Check your software if you are unsure which projection methods are available.

REMOVED VIEWS A removed view is a complete or partial view removed to another place on the sheet so that it is no longer in direct projection with any other view. Removed View Using View Indicator Arrow Removed View Using Viewing-Plane Line

RIGHT-HAND AND LEFT-HAND PARTS Often, parts function in pairs of similar opposite parts, but opposite parts can rarely be exactly alike. On sketches and drawings a left-hand part is noted as LH, and a right-hand part as RH.

REVOLUTION CONVENTIONS Regular multiview projections are sometimes awkward, confusing, or actually misleading. Revolutions like these are frequently used in connection with sectioning. Revolved sectional views are called aligned sections.

Common Hole Features Shown in Orthographic Views

Common Features Shown in Orthographic Views

Common Features Shown in Orthographic Views Continued…