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N airn A cademy

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Isometric Circle – 30 o /60 o generators method Start the isometric circle by drawing the front elevation and the plan of the cylinder to be drawn.

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Locating Lowest Corner + Drawing Isometric Crate Choose a suitable point ‘X’ on the elevation and plan and a suitable position to start the isometric view. x x x Draw an isometric crate to fit the isometric view into. Use 30 o and vertical lines for the angles of the lines. The overall size of the crate should be the exact size of the isometric view to be drawn.

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Finding Centre for Isometric Circle Draw centre lines on the isometric view. Use 30 o and vertical lines for this. x x x

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Finding Points on Circumference of Circle Divide the orthographic circle into 12 equal parts using 30 o and 60 o lines generated out from the centre. x x x Number each of the points where the generators cut the circumference of the circle – usually done in the same format as a clock.

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Transferring Circumference Points to Isometric (1) Project points where generator lines cut circumference of circle down and up to horizontal centre line of circle. x x x Measure horizontal sizes of projected points along centre line with compasses and transfer these sizes onto 30 o isometric centre line. Project vertical lines through these points so that circumference points can be found.

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Transferring Circumference Points to Isometric (2) Using compasses, measure the vertical distances from the centre line up and down to each of the points on the circumference in turn. Transfer each of these dimensions onto the isometric view. Number each of the points. x x x

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Drawing Isometric Curve Draw a smooth curve through each of the points to show the circumference of the isometric circle. x x x

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Determining Thickness of Cylinder To show the thickness of the cylinder in the isometric view it is necessary to project each of the points found back at 30 o. x x x Measure the thickness of the cylinder on the plan using compasses and transfer these sizes onto the isometric. (In this case all of the sizes are the same but this may not always be the case). It is not necessary to transfer all of the dimensions as all of the points will not be seen at the end – however if in doubt it is better to transfer all and then only use the required ones.

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Drawing Back Curve of Cylinder It is necessary to find two final points – the tangent points - to indicate how far out past points 4 and 5 and points 10 and 11 that the curve passes. This can be done in two ways – by finding points A and B on the elevation and transferring these points to the isometric in the same way as points 1 to 12. x x x A B A B – or by drawing diagonal lines on the isometric to find where the corresponding points occur on the front curve in the isometric. These points can then be projected back and measured as before to find the final positions. Finally, draw a smooth curve through each of the points found.

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Finishing Isometric View To finish the drawing darken the required part of the outline of the curve. x x x A B A B Complete the two edges to join the two curves together.

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The Final Drawing This is the final Isometric View of the cylinder. x x x

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PowerPoint Presentation produced by John McRae, Nairn Academy 2003

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