| By Mike Sloggatt |
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When working with circles--of ANY kind, always remember
THE RADIUS RULES
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An ellipse is defined by the Major
Axis (or total run), and the Minor Axis (or total rise)
The Semi-Major Axis is half the Major Axis
The Semi-Minor Axis is half the Minor Axis
The Semi-Major Axis plays a
critical role in shaping an ellipse. |
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The shape of an ellipse is determined by the Semi-Major
Axis (half the length of the run or span).
First, determine the rise of the ellipse desired.
Next, using the length of the Semi-Major Axis, swung
from the top of the ellipse, strike two intersection
points along the Major Axis.
These are the Focal Points.
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Use a thin wire to draw an ellipse.
Single-strand picture-framing wire works best.
1. Drive a screw or nail into each end of the Major
Axis.
2. Stretch wire from screw to screw, tightening the
wire securely on each screw.
3. Loosen the screws and insert them at the Focal
Points.
4. Pull the slack up to the top of the ellipse and
use a pencil to scribe the shape.
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The next time you have to cut a hole in the roof
for a piece of pipe...especially if the hole needs to
be finish-carpentry quality, use the string method to
layout the ellipse.
Click
here for a Sketchup Drawing & Tutorial |
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| Using a string isn't the only way to layout or cut an
ellipse. Here's
the trammel arm I use, with my router, for cutting elliptical
shapes. |
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