SolidWorks Geeks

how offset curves are constructed?

This might seem an easy concept, but actually few people might know what the resulting geometry of an offset command is. it's actually a mathematical subject that can be verified visually.an offset curve is an envelope of the curve which means it's constructed so that it's always remains tangent to a circle(Diameter=offset distance) which rolls over the curve. thats why an offset of an ellipse or a conic is not an ellipse.
see video attached, which shows the concept visually.

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Permalink Reply by Fabio Miguez on September 18, 2008 at 9:35am
Hi Arash,

Thanks for this info. I watched the video, and my question is isn't the inside offset an ellipse? You mentioned an offset is not a true ellipse, but I guess I am missing something.

Thanks,
Permalink Reply by Mark Treadwell on September 18, 2008 at 10:42am
Fabio,

Try it and see. Sketch an ellipse, and create an offset. Then create another ellipse with the same center and coincident to the offset at its control points. The two are generally similar in shape, but the offset entity will be "fatter" at the NE, NW, SE, SW regions - see below.

-Mark

Permalink Reply by Fabio Miguez on September 18, 2008 at 2:33pm
Hi Mark,

I see what you mean. Pretty interesting, and excellent to know! Thanks for the pic, by the way.
Permalink Reply by Arash on September 18, 2008 at 11:08pm
you can think of the outer curve as the toolpath to cut an elliptical contur. as you can see (mark's pic) the toolpath(which is the offset of the ellipse) is not an ellipse.

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