This Week's Topic's

Orthographic Sketching and Scales

Orthographic Sketching

Sketching is a rapid, freehand method of drawing rather drawing with instruments. Sketching is a thinking process as much as method of communication Although the angle bracket shown here is a simple 3-Dimensional object, describing it with words is difficult.

This figure shows all six of the two dimensional views of the bracket. The top view appears above the front view because both share the dimension of width The side view appears to the right of the front view because they share the dimension of height The space between views may vary, but the views must be positioned as shown here This arrangement is logical, the views are easiest to interpret in this order, since the views project from each other

This figure illustrates the lack of clarity when views are incorrectly positioned, even though each view is properly drawn

When sketching all lines, except construction lines, should be black and dense.

When making a freehand sketch, lines will be vertical, horizontal, angular, or circular

Since no tools are used in sketching, your sheet does not need to be taped, you can position the sheet for the most comfortable strokes

This figure shows examples of correctly sketched lines are contrasted with incorrectly sketched ones

The maximum number of principal views that may be drawn in orthographic projection is six In each view, two of the three dimensions of height, width, and depth are seen Most objects can be adequately described with three orthographic views

Usually the views used are the

Top

Front

Left or Right side

To obtain the views to describe an object First sketch the overall dimensions of the object. Then sketch the slanted surface in the top view and project it to the other views. Finally darken the lines, label the views and letter the overall dimensions of height, width, and depth. Slanted surfaces will appear as edges or fore-shortened (not true size) planes in the principal views of orthographic projection. When two intersecting planes of the object slope in two directions, both appear fore-shortened in the front, top, and side views.

Scales

All engineering drawings require the use of scales measuring lengths and sizes Scales may be flat or triangular.

The three most used types of engineering scales are:

Architects - For indoor architectural details

Engineers - For outdoor engineering (streets. land plats, etc...), and mechanical engineering

Metric - Used for most applications where the metric system is in use

Architects Scale

Place the scale designation in the title block or in a prominent location on the drawing To use the 1=1'-10 scale to measure a line Read the nearest whole foot (2' in this case) Then the remainder in inches from the end of the scale (3" in this case) For a total of 2'-3 Note that at the end of each scale, a foot is divided into inches for use in measuring dimensions less than a foot. The scale 1" = 1'-0 is the same as saying that 1 in. is equal to 12 in. Or that the drawing is 1/12 the actual size of the object

Engineers Scale

On the engineers scale each inch is divided into multiples of 10 Each end of the scale is labeled 10, 20, 30, etc. which indicates the number of units per inch on the scale Many combinations may be obtained simply by mentally moving the decimal places of a scale To use of the 10 scale to measure a line 32.0 ft long drawn at the scale of 1=10' And the 20 scale to measure a line 540.0 ft long drawn at the scale of 1=200'

Sketching is the graphic equivenlent to thinking aloud