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CAD tip CAD tip # 10039:

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Q - question

Two types of equidistants (offsets) to an ellipse.

A - answer An offset curve to an ellipse doesn't form a mathematical ellipse. In Inventor or in AutoCAD you can either create a true equidistant curve to an ellipse (with constant offset) - i.e. a spline, or an "offset" ellipse, i.e. a true ellipse with non-uniform offset along its circumference.

In Inventor you can choose between these two types of offsets in the context menu of the Offset command (O) - the default mode "Constrain Offset" creates true offset ellipse. If you disable the "Constrain Offset" mode after you select the source ellipse, Inventor will create an equidistant curve, a spline.

Example: Offset to the inner ellipse - the red one is a spline (disabled constrain):

ellipse geometry

In AutoCAD, the OFFSET command creates an equidistant curve, i.e. a spline. If you want to make a derived ellipse, use e.g. the LISP utility "OffsetEllipse.lsp" - see OFEL (true offset ellipse).

100% *  CAD 
7.10.2014    3487x  
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applies to: Inventor · AutoCAD ·

See also:
Tip 10138:Dimensioning a curve length or distance between two points on a curve.
Tip 7800:How to model a 3D hyperboloid?
Tip 6650:Break curve at all listed distances (stations).
Tip 6433:Force layer for selected commands (objects).
Tip 6388:How to convert an Ellipse to a Spline?

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