Offseting elliptical arches

[henry]

I need help with offset copying an elliptical arch to make 3 1/4" trim. When I do the inside elliptical like I want and then select it to offset copy to get my 3 1/4" + the diameter of the bit, It will not be the same distance in the tight radiuses of the elliptical. It comes up shy of 3" in the tight turns. My question is why want it remain the same distance all the way around the elliptical? I have created a work around on this problem, but it involves drawing 3 radiuses and hope that I connect them at the right place, then when I do an offset it stays the same...

Thanks

Henry

[gerald_d]

Henry, a line equidistant around an ellipse is no longer a true ellipse. You cannot make concentric ellipses like you can do with circles - the laws of maths don't allow it.

Your work-around (breaking into radii/arcs) is the only way to get a consistent 3.25". If you want help with the selection of the radii, mail (mailto:gerald@scapenotes.com) me your dxf file. (you probably need to keep the center-line of the 3.25" on an "ellipse", and then put 1.625" either side of that)

[harold_weber]

Henry, my CAD program has a feature that is best described as "construct a new line parallel by a user-specifiable distance either side of an existing line". This sounds like it would save you some trouble. My CAD program is Design CAD, but other CAD programs probably have this feature as well.