3D Modeling and Drawing Fundamentals (Graphing Communication)
December 2nd, 2011 Overview: Mechanical Drafting/Drawings Drawing Fundamentals o Engineering & Technical Drawings o Handouts & Exercises o Working Drawings o Dimension & Tolerance Introduction to Good Modeling Practices
Mechanical Drafting/Drawings CAD does not replace mechanical 2D drawings 2D drawings are the primary graphical communication method Helps in any field o Standard for most companies Standards exist to unify communication methods o Ensure consistency in understanding and interpretation 3D models are not the deliverable product 2D drawings for production are important, 3D doesnt matter without 2D
Introduction The need for standardization o Rules, nothing is up for interpretation US established by the American Society for Mechanical Engineers (ASME International Organization for Standardization sets worldwide standards
Technical Drawings Description of shape, size, features, and precision of physical objects Other information given in an easily recognizable way to anyone familiar with engineering drawings Principally used in FRC Applicable across many fields
Pictorial Drawings Like photographs Show objects as they would appear to the eye of the observer
Not used for technical designs because the interior features and detail are better seen with orthographic drawings 3 types o Oblique front face flat, 45 degree sides o Perspective vanishing points o Isometric 30, 60, 90 degree lines (most common)
Orthographic Projection Method to convey information about all features (hidden and invisible) of a part Front view, right side view, top view, etc Systematically arranged on drawing sheet, projected from one another Understand and visualize object Applied in four angles or systems
Third Angle Projection Imagine shape in glass box (top view is top of box, front view is front of box, etc) o Open/unfold box Six principle views (show less/more depending on symmetry of object) o Front view center o Top view - above o Bottom below o Left left o Right right o Back (rear) extreme left / right
ISO Projection Symbol Tow systems of orthographic projections o Must clarify which is being used o Adjacent to title block on drawing
Line Types Visible lines o Thick solid line, stands out, makes shape of object obvious
Hidden Lines Series of short dashes, varies by size, illustrates interior features, show true shape, may be omitted to preserve clarity To show continuity leave gap before line If it is a separates surface, dont leave a gap
Circular Features Appear circular in only one view No line is used to indicate where curved meets flat Hidden circles represented by hidden (dashed circle) and center lines (cross with long dash short dash long dash both ways) Often only two view required for circular/cylindrical parts
Drawing Views and Sheets How many are required? o As many as necessary to clearly show all features, sections, details and dimensions to fully explain the part and tolerances required to make it o Some simple parts can take many sheets with dozens of views to ensure complete definition
Section Views cut the part in half to show interior details Use double-dash long segment double dash
Section Lining Use hash marks to show that it is cut (like saw marks in a cut), parallel lines 45 degrees to principle of the cut
Types of Sections Full Section Half/Partial Section Offset Pection
Dimensioning Extension lines, dimension lines, leaders, arrowheads, figures, notes symbols Come off part you are trying to dimension, arrow heads point to feature you are dimensioning Define geometrical characteristic (distances, diameters, angles, locations Lines used are thin in contrast to object outline Clear and concise (no ambiguity) No redundant dimensions dont put two dimensions per feature
Placement of dimensions Unidirectional (preferred Aligned (with feature that is dimensioned, will go sideways sometime)
Dimension Lines Line that shows extension lines, ends with arrows, connects extension lines With small ones, arrows are on outside Not on part itself - important
Extension Lines Extend from part
Leaders Direct dimensions or notes to the surfaces or points to which they apply Ends with arrowhead or dot (for surface)
Dimensioning Units of Measurement Decimal inch system (US customary) Fractional inch system Feet and inches system
Rules for dimensioning Place the dimension line for the shortest width, height, and depth nearest the outline of the object o Parallel dimension lines are placed in order of size Place dimensions near the view that bests shows the shape or contour of the object Chain dimensioning all continue in a line Parallel dimensioning all dimensions start from same surface
Dimensioning Hole Features Countersinks o Dimensioned with diameter of hole, countersink, then angles of countersink Counterbores (Spot Face) o Dimensioned with diameter of hole, counterbore, then angles of counterbore Clearance Hole o A hole slightly larger than the nominal size of item using the hole Rounds o External intersection of faces that are rounded Fillets o Internal Chamfers o Intersection of faces that is cut away
