how do you scale down a circle with a stroke (and no fill), so the the strokes touch each other ?

lets say i have a circle 600x600px, with a stroke of 9px

(the Affect - Scale Stroke Proportion is turned off)

the obvious logic would be to make the second circle 9px smaller = 591px, but that doesnt work
so how does the Stroke calculate ?

Hi.

The size of your circle is the outside diameter of the stroke.
To resize a copy of the circle so that it will fit inside the original;
old circle diam - (2 * stroke width)
in your case the new circle size will be; 600-(2*9)=582 (pixels)

RGDS
Ragnar

that was quick

thanks !

An idea is to use the interpolate subpaths live path effect.

Draw a circular path, duplicate it, scale down, then combine it with the original and add the lpe.
That way it is easier to get a close match without calculations.
(Like the original circle's diameter is 574,985 px, with a 8,275 px stroke given it would be harder to be calculated)