Chapter 2 Freehand Sketching PDF

Chapter 2 Freehand Sketching  Objectives After completing this chapter, the students will be able to Create freehand sketches using the correct sketching techniques. Explain the difference between axonometric and oblique projection. Explain the difference between isometric pr...

Chapter 2 Freehand Sketching  Objectives After completing this chapter, the students will be able to Create freehand sketches using the correct sketching techniques. Explain the difference between axonometric and oblique projection. Explain the difference between isometric projection and isometric sketch (or draw). Create an isometric and oblique sketches from an actual object and given multiview drawing.  Topics Freehand sketch Pictorial projections - Axonometric - Oblique Isometric sketch Oblique sketch Freehand Sketching  Basic geometry Straight line : Horizontal, vertical and Inclined. Arc & Circle  Sketching Lines 1. Hold the pencil naturally. 2. Spot the beginning and end points. 3. Swing the pencil back and forth between the points, barely touching the paper until the direction is clearly established. 4. Draw the line firmly with a free and easy wrist-and-arm motion. Sketching Lines  Sketching Arc Method 1 : Starting with a square Method 2 : Starting with a center line  Sketching a Small Circle Method 1 : Starting with a square 1. Lightly sketching the square and marking the mid-points. 2. Draw light diagonals and mark the estimated radius. 3. Draw the circle through the eight points. Step 1 Step 2 Step 3 1/3 2/3  Sketching a Small Circle Method 2 : Starting with center line 1. Lightly draw a center line. 2. Add light radial lines and mark the estimated radius. 3. Sketch the full circle. Step 1 Step 2 Step 3  Sketching a Large Circle 1. Place the pencil’ s tip at the center as a pivot, and set the pencil point at the radius-distance from the center. 2. Hold the hand in this position and rotate the paper.  Pictorial Projections  Pictorial Projection Axonometric Projection Oblique Projection Parallel & normal to picture plane Parallel & oblique to picture plane B A D A Line C B A of A Line B B sight of C D sight C C D D  Axonometric Projection B A D Line C of B A sight D C  Axonometric Projection Type of axonometric drawing Axonometric axis a 1. Isometric All angles are equal. b c B A B a Axonometric axis A D C 2. Dimetric c Two angles are equal. D b C a Axonometric axis 3. Trimetric b c None of angles are equal.  Oblique Projection A A Line B B of C sight C D D  Oblique Projection Oblique drawing angle 60o 45 o A 30o B C A B Type of Oblique drawing D 1) Cavalier 2) Cabinet C D Full scale Half scale 45o 45o Isometric projection vs. Isometric sketch Isometric Projection Rotate 45 about vertical axis Tilt forward (35o16’) All edges foreshorten about 0.8 time.  Isometric sketch Isometric sketch is an isometric view that is drawn in full size. Isometric projection Isometric drawing (True projection) (Full size) Forshorten Full scale  Orientation of Isometric Axes Isometric axes can be arbitrarily oriented to create different views of a single object. Regular Reverse axis Long axis isometric isometric isometric View point is looking View point is looking View point is looking down on the top of up on the bottom of from the right (or left) the object. the object. of the object.  Distance in Isometric Sketch True-length distances show along isometric lines. Isometric line is the line that run parallel to any of the isometric axes. Nonisometric lines Isometric axes Isometric Sketching  Sketch from an actual object 1. Place the object in the position which its shape and features are clearly seen. 2. Define an isometric axis. 3. Sketching the enclosing box (or cylinder). 4. Estimate the size an and relationship of each details. 5. Darken all visible lines.  Sketch from an actual object STEPS 1. Positioning object. 2. Select isometric axis. 3. Sketch enclosing box. 4. Add details. 5. Darken visible lines.  Sketch from an actual object STEPS 1. Positioning object. 2. Select isometric axis. 3. Sketch enclosing box. 4. Add details. 5. Darken visible lines. Note In isometric sketch/drawing), hidden lines are omitted unless they are absolutely necessary.  Sketch from multiview drawing 1. Interprete the meaning of lines/areas in multiview drawing. 2. Locate the lines or surfaces relative to isometric axis. Example 1 : Object has only normal surfaces Top H Regular Top View Front Side W D Front View Side View H W D Side Reverse Front Bottom View Bottom Example 2 : Object has inclined surfaces D Nonisometric line y q H y x x Front View W Example 4 Regular x y C E B D F Front View A B C D Reverse A F E  Isometric ellipse In isometric drawing, a circle appears as an ellipse. Sketching Steps 1. Locate the center of an ellipse. 2. Construct an isometric square. 3. Sketch arcs that connect the tangent points.  Isometric ellipse Four-center method is usually used when drawn an isometric ellipse with drawing instrument. Sketching Steps 1. Locate the center of an ellipse. 2. Construct an isometric square. 3. Construct a perpendicular bisector from each tangent point. 4. Locate the four centers. 5. Draw the arcs with these centers and tangent to isometric square. Example 5  Irregular Curve in Isometric Steps 1. Construct points along the curve in multiview drawing. 2. Locate these points in the isometric view. 3. Sketch the connecting lines.  Oblique Sketching  Object Orientation Guidelines Complex features (arc, hole, irregular shape surface) are placed parallel to frontal plane.  Object Orientation Guidelines The longest dimension of an object should be parallel to the frontal plane. GOOD GOOD WORSE WORSE  Object Orientation Guidelines Which one is better ? Sketch from actual object ESTIMATE DEPTH ESTIMATE LINES D 45  Sketch from multiview drawing Example 1  Sketch from multiview drawing Example 1  Sketch from multiview drawing Example 2 E D C B A  Sketch from multiview drawing Example 2 E D C B A  Sketch from multiview drawing Example 2 E D C B A  Sketch from multiview drawing Example 2 E D C B A