Graphic Communication Boclair Academy Graphic Communication Department of Technological Education

Cut Oblique Cone Department of Technological Education The Elevation of a cut Oblique Cone is shown. Draw the Plan of the cone. Draw the Surface Development of the cone. O PLAN O ELEVATION

Drawing Generators to Apex Department of Technological Education Drawing Generators to Apex Start by drawing the circle shape of the cone in Plan. Divide the Plan into 30o parts, project the points down to the Front Elevation and number each of the points found. 1 3 5 7 9 11 12 1O 8 6 4 2 O Project generators for these lines to the apex of the cone on the Plan. PLAN 1/5 12/6 10/8 9 2/4 11/7 3 Repeat this process for the Front Elevation. O ELEVATION

Drawing Cut in Plan Department of Technological Education Find the point where each generator on the Elevation passes through the top cut. Project these points back up to the appropriate generator on the Plan. O ELEVATION PLAN 1 3 5 7 9 11 12 1O 8 6 4 2 1/5 12/6 10/8 2/4 11/7 Draw a smooth curve through each of the points found and darken in the remainder of the outlines.

Finding True Length Lines Department of Technological Education Finding True Length Lines Before you can start drawing the Surface Development of the Oblique Cone, it is necessary to find the True Length of each of the generators. Each Plan generator needs to be rotated to be horizontal with point ‘O’ using point ‘O’ as the centre of the rotation. This process is normally done to the side of the existing views for clarity. O ELEVATION PLAN 1 3 5 7 9 11 12 1O 8 6 4 2 1/5 12/6 10/8 2/4 11/7 9 10/8 11/7 12/6 1/5 2/4 3 9 10/8 11/7 12/6 1/5 2/4 3 Each generator is now projected down to the base of the Elevation. (the base in this drawing is actually the top surface. Angled lines are now drawn on the Elevation to point ‘O’. These lines are the True Lengths of each of the generators.

Drawing Surface Development Department of Technological Education Drawing Surface Development To draw the Surface Development it is wise to use two pairs of compasses if possible. One can be set to the longer True Length sizes and adjusted when required, with the other set to the smaller 30o segment distance from the Plan. Starting with the longest generator, draw a vertical line and measure the length of the O9 True Length line. O ELEVATION PLAN 1 3 5 7 9 11 12 1O 8 6 4 2 1/5 12/6 10/8 2/4 11/7 O 3 3 4 2 1 For each subsequent point two arcs need to be drawn – one for the True length dimension and the other for the 30o segment dimension. Place a small dot where the two arcs cross to locate a point on the edge and number the points. 5 6 12 7 11 8 10 9

Drawing Cut on Development Department of Technological Education Drawing Cut on Development To complete the Development it is necessary to find the points for the cut top surface. The points on the Elevation should be projected onto the appropriate True Length line. O ELEVATION PLAN 1 3 5 7 9 11 12 1O 8 6 4 2 1/5 12/6 10/8 2/4 11/7 10 Measure the dimensions from ‘O’ to each cut point and transfer this size to the correct generator on the Development. Two other points need to be found – the two end points of the cut. These sizes should be measured on the Plan and transferred to the Development. Note that in this situation the dimension is measured from point 6 towards 5 (and 12 to 1) as this gives the larger of the two alternatives and is more accurate

The Completed Drawing Department of Technological Education To complete the drawing the curves and the outlines should be darkened in. O ELEVATION PLAN 1 3 5 7 9 11 12 1O 8 6 4 2 1/5 12/6 10/8 2/4 11/7 10

PowerPoint Presentation produced by John McRae, Nairn Academy 2003