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Arc - Two points and tangent


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I have a horizontal line going across the screen, and two points south of the line spaced apart. How to make the arc's tangent intersect with the horizontal line? Please see image attached.

Screenshot 2024-02-10 195017.png

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An interesing construction that can be solved with AutoCAD's parameric features.  


In the figure below the red line ends are at the two fixed points.  The magenta line is its perpendicular bisector.  The yellow line goes from a point that will be the tangent point of the circle to the fixed horizontal white line. The other end of the yellow line is fixed at either of the two fixed points. The green line s the perpendicular bisector of the yellow line. The solution ca be found when the tangent point is directly above the intersection point of the two perpendicular bisectors.  That is, when d1 = 0.0.




Here d1 = 0.0




circle tangent 2 points.dwg

Edited by lrm
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But it does work. Obviously you have not tried it, but it is an oddity in AutoCAD.


If you use the command ARC, then when trying to draw an arc with three points, Tangent to the line does not work.


However, if you use the command CIRCLE with the 3P option, Tangent to the line does work. it turns into deferred snap mode.


I have been using it like that for a long time with my ancient version of AutoCAD. Perhaps the modern version cannot do it?

Edited by eldon
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@eldon if you use osnap tangent for the thrid point and pick the line it does work. I didn't think to try that as the line is not a point and you have to create a circle and not an arc first (similar to circle TTR vs fillet).  You learn something new everyday! Thanks.  


Solving this with paramerics was fun anyway.

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Thank you so much for your replies. I have also found multiple solutions including using geometry that involves two large circles, using tangent parametric, the onsnap tangent works for me too but only if I uncheck other snap modes.


Thanks again for the support.


My problem is solved.

Screenshot 2024-02-12 181147.png

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