Create a circle tangent to a line

Sometimes you want a circle to hug a line perfectly. You could try to eyeball it, but there’s a better way–the tangent options of the CIRCLE command. There are two, TTR and TTT. The TTT option is something of a secret, because it doesn’t appear as an option on the Command line. I have no idea why. It does appear on the ribbon, though.

TTR (Tangent, Tangent, Radius)

Let’s say that you know your circle’s radius needs to be 120 inches, because you have a pre-made pool that you can buy that is 240 inches across (the diameter). You want to fit the pool between two paths that look like this.

Here are the steps to creating a circle that is tangent to the inside of the path:

1. Choose Home tab> Draw panel> Circle drop-down> Tan, Tan, Radius.
2. At the Specify point on object for first tangent of circle: prompt, click anywhere on the inside line of the vertical path.
3. At the Specify point on object for second tangent of circle: prompt, click anywhere on the inside line of the horizontal path.
4. At the Specify radius of circle <10′-0″>: prompt, type 120 and press Enter.

Add a few embellishments and you’ll get something like this.

Check out this exercise to Draw a circle with radius tangent to two objects

TTT (Tangent, Tangent, Tangent)

When you want to specify 3 sides of a circle tangent to a line, use Tangent, Tangent, Tangent.

Let’s say you have a triangular courtyard and want to fit a pond inside it. Here’s where Tangent, Tangent, Tangent can help you. Your courtyard looks like this.

Here are the steps:

1. Choose Home tab> Draw panel> Circle drop-down> Tan, Tan, Tan
2. At the Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: _3p Specify first point on circle: prompt, click anywhere on the inside of one side of the courtyard.
3. At the Specify second point on circle: _tan to prompt, click anywhere on the inside of a second side of the courtyard.
4. At the Specify third point on circle: _tan to prompt, click anywhere on the inside of the third side of the courtyard.

From the prompts, I think you can see that Tan, Tan, Tan is a special case of the CIRCLE command’s 3P option.

Again, add a few finishing touches to get something like this.

Do you create tangent circles? In which situations are they useful for you?

Want more productivity tips like this? You can draw and edit faster and easier with this easy to follow top 25 productivity tips every AutoCAD user should know.

• Author
• Recent Posts

Ellen Finkelstein

Ellen Finkelstein is the author of the best-selling AutoCAD & AutoCAD LT Bible, which started with R14. Ellen has written extensively on AutoCAD, including articles for Autodesk’s website and features for AutoCAD’s Help system. Ellen’s first book was AutoCAD For Dummies Quick Reference.

Latest posts by Ellen Finkelstein (see all)

• Combine or subtract 2D shapes to create custom shapes - February 17, 2022
• Working with linetype scales - January 18, 2022
• Rename named objects–blocks, dimension styles, layers, and more - December 21, 2021