2Freehand SketchingFreehand sketches are a helpful way to organize your thoughts and record ideas. They provide a quick, low-cost way to explore various solutions to design problems so that the best choices canbe made.
3TECHNIQUE OF LINES line patterns The chief difference between a drawing and a freehand sketch lies in the character or technique of the lines.A good freehand line is not expected to be as rigidly straight or exactly uniform. A good freehand line shows freedom and variety, whereas a line drawn using CAD or instruments should be exact.line patterns
4LineweightsEven in freehand drawings, thick lines should be twice the width of thin lines.Thicknesses do not have to be exact, but there should be an obvious difference between thick and thin lines. Because visible lines and cutting-plane lines are the two thick line patterns, other lines should be distinctlythinner in comparison.To draw thick and thin lines freehand,you might like to keep two pencilshandy, one that is razor sharp for thinlines and another that is dulled, tocreate thicker lines. As the sharp pointbecomes dulled, switch it with thedull pencil, and sharpen the other,so that there is always one sharpand one dulled point ready to use.
5FREEHAND LINESThe main difference between an instrument or CAD drawing and a freehand sketch is in the appearance of the lines. A good freehand line is not expected to be precisely straight or exactly uniform, as is a CAD or instrument-drawn line. Freehand lines show freedom and variety.Freehand construction lines are very light, rough lines. All other lines should be dark and clean.
6Edges and Vertices Edges Vertices Points An edge of the solid is formed where two surfaces intersect. Edges are represented in drawings by visible or hidden lines.VerticesA vertex (plural, vertices) of a solid is formed where three or more surfaces intersect..PointsA point is used to represent a location in space but has no width, height, or depth.
7For Example: 1. Visible 2. Hidden 3. Center From Bertoline: Figure 2.38 / Pg 42In engineering and technical drawing, it is important that hidden features be represented, so that the reader of the drawing can clearly understand the object.Thus we need hidden lines to emphasize that those features exist and are hidden in that particular view.We also need center lines to understand how the features defined in the 2D views translate into 3D.NOTE: It must be emphasized that hidden lines and center lines are used only on Orthographic projection drawings, never on isometric drawingsQ: Do we need a convention for what line to show if two lines fall on top of each other?A: Yes! Otherwise features which are more important (eg: visible lines) would be overridden by less important features (eg: hidden lines) and the resulting drawing would be interpreted inaccurately. The next slide shows the convention followed.2. Hidden3. Center
9Small 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 1Step 2Step 3
10Arc Method 1 : Starting with a square Method 2 : Starting with a center line
13PROPORTIONSSketches should be proportional. A square should look like a square, and a rectangle like a rectangle. Graph paper is very helpful in sketching proportionally, but it is still sometimes difficult to be accurate even with graph paper.
14CURVESCurved shapes are best sketched by first defining points along the curve, then lightly sketching the curve between the points.
15Circles and EllipseAn ellipse can be sketched by first sketching a perpendicular axis, then locating four marks on the centerlines that are approximately equal to major and minor axis distances. Sketch a light curve, make any corrections necessary, anddarken in the elliptical shape.
16Introduction to Isometric Projection CUBEIsometric Projection:One type of axonometric pictorial (3-D) projection‘Iso-’ means ‘equal‘metric projection’ means ‘a projection to a scaled measure’The three dimensions are not only shown in one view, but also the dimensions can be scaled from this drawingSTART WITH A CUBEAll of the normal drawing planes (top, front, side) are equally foreshortened or tilted, and all of the major axes (X, Y, Z) are at equal rotations from each other (120 degrees apart), as in the illustration above.And, because all of the major planes are equally foreshortened, all of the measurements in these planes are equal as well as shown above. This means that the same measuring scale may be used in drawing both the width, height, and depth of objects.Isometric means equal measureAll planes are equally or proportionately shortened andtiltedAll the major axes (X, Y, Z) are 120 degrees apartAU 2005
17Making an Isometric Sketch Defining Axis30o60oIsometric AxisDerive the axes from a vertex of the cubeAU 2005
18Three planes The three planes of an isometric axis are defined as the left, right, and top planes, respectively
19Making an Isometric Sketch Axis ConventionHeightChoose the longest dimension to be the width (or the depth) for optical stabilityWidthDepthThe above slide is used to indicate the manner in which the width, depth and height of a 3-dimensional object is seen in an Isometric Sketch.Note the assignments of height, width, and depth to the axis.The front view direction is shown. Please emphasize this convention to the students.Front viewIsometric Axis ConventionAU 2005
20Object for PracticeHow to derive this object from a rectangular piece of wood?Shape it in to a rectangle with maximum dimensions (so as to fit the required object) on the three axesChisel out the unwanted parts…. Slides follow.NOTE: No scale provided due to lack of measurements of blocks.TA’s – Get the blocks from the Instructors Console and distribute them to all the tables.AU 2005
21Blocking in the Object Begin with Front Face HeightWidthIdentify the size of the front view of the object and sketch its outside dimensions on the Isometric view.AU 2005
22Blocking in the Object: Add Side Face HeightDepthSide FaceOnce the front view outside dimensions are added on the isometric sketch, add the side view dimensions.AU 2005
23Blocking in the Object: Add Top Face After front and side views are sketched on the isometric drawing, then add the top view.AU 2005
24Adding Detail Cut Outs – Part 1 The order of adding the details is important. They build upon each other.AU 2005
25Adding Detail Cut Outs – Part 2 Note that lines parallel to axesAU 2005
26Adding Detail Cut Outs – Part 3 Note that lines parallel to axes are drawn first, then oblique lines are determined from their intersections.AU 2005
27Darken Final Lines - Part 4 Note:All visible edgeswill be darkenedConstruction lines can be left in but must be much lighter than the final lines.AU 2005
28PLANNING YOUR DRAWING OR SKETCH When laying out a drawing sheet, you willneed to consider:• the size and scale of the object you willshow• the sheet size• the measurement system (units) for thedrawing• the space necessary for standard notesand title block.