Isometric Circles

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Graphic Communication
Isometric Circles Trammel Method
CDT Department
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Isometric Circle trammel 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

• Draw an isometric crate to fit the isometric view
  into.
• Use 30o 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.

x
x
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Finding Centre for Isometric Circle

• Draw centre lines on the isometric view. Use 30o
  and vertical lines for this.

x
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Finding Points on Circumference of Circle

• Divide the orthographic circle into sections by
  drawing random vertical lines.
• There should be enough lines to be able to
  construct an accurate curve in the isometric so
  you should aim for a minimum of 4 points for each
  quarter circle.
• In the example shown there are 4 points for each
  part so this shows the minimum standard required.
• Number each of the lines.

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1
2
3
5
6
7
x
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Transferring Circumference Points to Isometric (1)

• Each of the random lines need to be transferred
  to the isometric view.
• This is done by placing a trammel on the centre
  line of the front view and marking where each of
  the random lines passes through the centre line.

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1
2
3
5
6
7

• Number each of the points.

1 2 3 4 5
6 7

• Using the trammel transfer each of the marks to
  the isometric view.

1 2 3 4 5
6 7
x

• Draw vertical lines through each of the points
  found.

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Transferring Circumference Points to Isometric (2)

• Using the trammel, measure the vertical distances
  from the centre line up and down to each of the
  points on the circumference in turn.

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1
2
3
5
6
7

• Transfer each of these dimensions onto the
  isometric view.

1 2 3 4 5
6 7
x
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Drawing Front Isometric Curve

• Draw a smooth curve through each of the points to
  show the circumference of the isometric circle.

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1
2
3
5
6
7
1 2 3 4 5
6 7
x
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Finding Thickness of Cylinder on Isometric

• Project each of the points on the front curve of
  the isometric back at 30o so that the width of
  the cylinder can be marked.

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1
2
3
5
6
7

• Measure the width of the cylinder on the plan
  using a trammel. Because the thickness of the
  cylinder in this case is constant only one size
  needs to be measured, although this may not
  always be the case.
• Transfer the size measured onto the isometric and
  mark each point found with a small dot.

1 2 3 4 5
6 7
x
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Finding Tangent Points on Isometric

• It is necessary to find two final points the
  tangent points.
• These points are found in the same way as the
  previous points.
• By drawing diagonal lines on the elevation and
  isometric you will be able to find where the
  corresponding points occur points A and B.

A
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1
2
3
5
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A
1 2 3 4 5
6 7

• These points can then be projected back and
  measured as before to find the final positions.

B
B
x

• Finally, draw a smooth curve through each of the
  points found.

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Drawing Back Isometric Curve and Tangent Edges

• To finish the drawing darken the required part of
  the outline of the curve.

• 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.

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