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## circles within circles...

Hi,

I've been hitting my head against a metephorical wall for the last hour trying to do something which seemed simple

Okay

I have a large circle and I want to put a smaller circle inside it so that the quadrant of each circle intersect at the o - Easy.
Circle2.jpg

I now want to draw a line parrallel to the centre line of the larger circle but offset (in y direction) by x units - Easy.
Circle3.jpg

Now for the tricky bit...

I want to rotate the smaller circle around so that it remains concentric with the larger circle (easy) and becomes parrallel with the offset line (so far impossible!)

What am I missing? I have tried everything I can think of: parallel onsap, geometric constraints, etc...

Thanks

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## Re: circles within circles...

Originally Posted by IamMichaelPacker747327
Hi,

I've been hitting my head against a metephorical wall for the last hour trying to do something which seemed simple

Okay

I have a large circle and I want to put a smaller circle inside it so that the quadrant of each circle intersect at the o - Easy.
Circle2.jpg

I now want to draw a line parrallel to the centre line of the larger circle but offset (in y direction) by x units - Easy.
Circle3.jpg

Now for the tricky bit...

I want to rotate the smaller circle around so that it remains concentric with the larger circle (easy) and becomes parrallel with the offset line (so far impossible!)

What am I missing? I have tried everything I can think of: parallel onsap, geometric constraints, etc...

Thanks
Sorry but I don't understand quite well. There seems to be some misunderstandings on the definition of terms.

1. concentric means sharing the same center. Your circles in the images are not concentric.
2. a circle cannot be parallel to a line.

If you mean that the smaller circle remains tangent to bigger circle, and its center passing thru the offset line,
1. Offset the bigger circle to the smaller circle's center.
2. The intersection of the new circle and the offset line will be the new center of the smaller circle.

Welcome to AUGI.

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## Re: circles within circles...

I agree, we may need more clarification.
But if you mean to move the smaller circle so the inside is tangent with the big circle at the offset line, see my suggestion below.

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## Re: circles within circles...

Hi,

Thanks for your comments you are right, I didn't mean concentric and parallel (clearly too much head bashing!). What I meant was: I want to rotate the small circle around the centre of the large circle so that it ends up being tangent to the offset line.

Hope that makes more sence?

Cheers,

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## Re: circles within circles...

So, similar to Ted's suggestion but use the "R" (reference) option of the rotate command and pick the intersections shown with green circles.

tangent.png

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## Re: circles within circles...

Thanks again, but I still can't quite achieve what I am after, even using th "r" command. What I want is that the smaller circle becomes tangential to the horizontally offset line - see below.
Circle4.png

Cheers

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## Re: circles within circles...

Instead of rotating, recreate the circle using the TTR option. Pick the circle and offset line for the tangents, then enter radius for small circle.

In case the radius is not a whole number, it is best to pick the radius from the circle itself when asked for the radius, to avoid inaccuracy. (i.e. osnapping NEAREST/QUADRANT to CENTER)

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## Re: circles within circles...

Originally Posted by tedg
I agree, we may need more clarification.
But if you mean to move the smaller circle so the inside is tangent with the big circle at the offset line, see my suggestion below.
That's what I thought of first too, but I don't think it's what the OP is after. The problem is the complexity of figuring out what rotation angle to use to get the second circle tangent to the offset line. It doesn't happen where the inside radius intersects the offset.

The solution instead may be fairly simple as mentioned just above (which I saw after I posted! . Draw the second (smaller) circle using the tan tan radius option. Tangent to the outside circle and tangent to the offset as shown here:

Dave.

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## Re: circles within circles...

Thanks guys. TTR option works a treat!

Cheers

10. 0 Did you find this post helpful? Yes

## Re: circles within circles...

Glad we could help, even though it was a long way around to the solution.
I think a little more info up front would have helped to get there quicker.

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