# How to Draw Arc That Tangent to 2 Circles?

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I know I can do it by using the Ttr command in AutoCAD, but that's not what I want to know.

Can someone please tell me how to draw an arc that tangent to 2 circles using traditional method (e.g. using compass)?

For example, how to draw such as below image in AutoCAD using traditional method with the given 2 known-diameter circle with a distance of 7 between its center point? How do you draw an arc with radius of 12 that tangent to these two circles?

Thank you

Edited by basty
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• basty changed the title to How to Draw Arc That Tangent to 2 Circles?

From the centre of the 1.5r circle, draw a circle of radius 10.5 (= 12 - 1.5)

From the centre of the 1r circle, draw a circle of radius  11 (= 12 - 1)

Where the two circles intersect is the centre of the arc of radius 12

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Just a bit of background an arc arc arc solution has 4 possible solutions. Autocad Fillet command has failed for years to improve TTR, whilst other software like from 1980 has an option for this, It has been commented on many times. The above would be 1 solution  given a known radius. The solution is pick a guess pt for the new arc center point. Then its a solution as offered in the prior post using geometry.

Edited by BIGAL
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• 1 month later...

What the maximum and minimum the radius is?

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The solution at moment is the TTR I know have this option on my wish list to do a solution. There may be some lisp out there but nothing last time this question was asked.

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