Tech Directions - February 2008 - (Page 19)

modeling software system. Consider the object shown in Fig. 1. It looks simple because it consists of only two features, a block of material with a 45° angled top and a 30° dovetail slot. However, the 30° dovetail slot requires a construction plane that is hard to create. The CAD operator begins by sketching the two-dimensional end view shape of the 45° angled part on the default construction plane. This sketch is then extruded to form a block of material. The second feature is a dovetail slot that cuts across the 45° angled surface. This feature is at an angle of 30° to the front edge (K in Fig. 2). The required construction plane for this dovetail slot must be perpendicular to the axis of the dovetail slot. How will the required construction plane be created? It would seem that the current construction plane must be rotated at least twice, but at what angles? Is the first angle of rotation 45° or 315°? What will be its axis of rotation? Assuming the first rotation angle is 45°, would the other required rotation angle be 30°, 60°, 120°, 150°, 210°, 240°, 300°, or 330°, or some other angle? What line would serve as the axis for this rotation? What plane should serve as the base plane for all rotations? When you find the construction plane, how do you position the dovetail shape so as to begin 1" along the front edge of the block of material when all measurements on the construction plane are different from measurements on the planes of the model due the angular relationships involved? In other words, 1" measured along edge K will not appear as 1" on the construction plane. Many CAD operators resort to trial and error when faced with a problem like this. But trial and error is not a productive approach. Aside from being time consuming, it may not result in a solution at all because there are a large number of possible wrong combinations of angles, axes, and alignments. F Celebrate Black History Month! Inspire your students with posters of African Americans who have had a major impact on the course of American history, from the research lab to the battlefield to the courtroom. Each 18" × 24" Black History Pioneers poster is sale priced at $9.95 SALE! Save over $50! All 14 Black History Pioneers posters $124.95 See them all at www. techdirections.com/posterscr.html Tech Directions Books & Media PO Box 8623, Ann Arbor, MI 48107 800.530.9673 ext. 200 www.techdirections.com CAD/CAM 19 http://techdirections.com/posterscr.html http://www.sunequipco.com http://www.studica.com/netop http://www.studica.com/netop http://www.sunequipco.com http://www.techdirections.com

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Tech Directions - February 2008 Technically Speaking Contents Direct from Washington The News Report Technology’s Past Technology Today Mastering Computers How Engineers Engineer—Lessons from My First Big Engineering Project Tips on Creating Complex Geometry Using Solid Modeling Software Press to Test—Shop-Built BJT Checker Is Easy Cable Television Technician International Technology Education Association Conference—Teaching TIDE with Pride Professional Development Opportunities Product Central Free for the Asking More than Fun

Tech Directions - February 2008

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