TheSwamp

CAD Forums => CAD General => Topic started by: notredave on August 05, 2020, 10:52:53 AM

Title: Isocircles
Post by: notredave on August 05, 2020, 10:52:53 AM

Good morning,

I am having a time trying to get an ellipse-->isocircle in isodraft to give me the correct diameter when I do a distance between quadrants. For example, if I draw an isocircle with a diameter of 1" and dimension it, it gives 1.2247" across quadrants. Is there a way to draw an isocircle with diameter inputted to output correct diameter when dimensioning it?

Thank you,
Dave

Title: Re: Isocircles
Post by: Crank on August 05, 2020, 03:35:39 PM

It's just math (in radians)
If you draw a circle with radius=1 and add some lines and angles, we get:

Code: [Select]

(setq Rmin (cos (* pi .25)))
(setq Rmax (* Rmin (sqrt 3.)))
So:

Code: [Select]

(setq Rmin (* 0.5 (sqrt 2.)))
(setq Rmax (* 0.5 (sqrt 6.)))