Tangent to circle problem

[clemson77on]

I'm sure this has been covered on here, but I had no luck with a search for it. I'm trying to draw an arc to the tangent point of a circle but it goes to the inside when I snap to the tangent. I don't know what the radius is supposed to be. I just need the bottom quadrant of the formed arc to be at the top quadrant of the circle on the right.

[eldon]

I think that you will find that there is no exact geometrical solution, so AutoCAD is doing the best that it can without exact information.

 

You can find the radius of your circle, by successive approximation, but I don't think that AutoCAD can.

[bradbb2005]

Can you trim that piece off or is it needed?

[CarlB]

I think you can do it with the "3 point" option-

-pt1 is top quad of circle 1 (right)

-pt2 is "tan" to circle 1, pick near pt1

-pt3 is "tan" to circle 2

[paulmcz]

I'm sure this has been covered on here, but I had no luck with a search for it. I'm trying to draw an arc to the tangent point of a circle but it goes to the inside when I snap to the tangent. I don't know what the radius is supposed to be. I just need the bottom quadrant of the formed arc to be at the top quadrant of the circle on the right.

 

Draw vertical xline through center of circle B

 

copy circle A by upper quadrant point to upper quadrant point of circle B

 

draw a line from center of just copied circle to the center of circle A

 

draw xline perpendicular to line connecting the two centers, through its midpoint

 

Intersection of the two xlines is the center of the arc you want to draw

 

See the attached sketch

TangToCircles.pdf

[Coosbaylumber]

We used to solve such without aide of Autocad, but after R-14 sometime found the tangent did not go "exactly" to tangent but to nearest point on the circle. I used to visit the Autodesk site and they said it happened by about R-2004 when they went to a M-S based calulation. None of the Reps. from Autodesk said there was any problem, and was zero complaints too. I had it investigated here, and got a few responces, as like it is used only once or twice per year by them too. You got the same problem as they have in Cheapcad now.

 

I had to go back to my old pencil notes to solve the bad lines.

 

 

Wm.

[eldon]

Having just had a play, CarlB's method works in AutoCAD 2002.

 

So full marks to the three point circle.

[clemson77on]

paulmcz- Thanks! I was able to get that to work.

 

Carl- I couldn't get that to work. I was probably doing something wrong, but I never got tangent options on point 2 & 3.