Double-click the tool in the Toolbar.
The options in the dialog box adjust the curvature of the arc or the amount of bending but do not affect the angle. Imagine two line segments with their ends meeting at a 45 degree angle. I want to to draw an arc inside that angle.
Illustrator doesn't do tangents.
No, not really but you can quite easily construct tangents:
Start off by drawing a circle of the required radius.
With Smart guides turned on, use Line or Pen tool to draw radii at the required angles.
Rotate-copy the radii each by 90° about the points where they intersect the circle and bingo.
Now all you have to do is a bit of Pathfinding to get rid of the bits you don’t want.
Depending on the exact goal, you may do it with the normal tools or a free script. I apologize if the following is old news or completely off the goal.
If you just wish to round the corner(s), you may use Effect>Stylize>Round Corner with the desired radius; you may Object>Expand Appearance to create a rounded segment.
If you only wish to round one or more, but not all corners, you may use the free Round Any Corner script available here:
If you wish to create a separate arc inside one or more sharp corners, you may:
1) Copy the angular path,
2) Effect>Stylize>Round Corner with the desired radius,
3) Object>Expand Appearance,
4) Direct Select the relevant rounded corner(s) and Ctrl/Cmd+X+F,
5) Delete the rest of the copy path.
There are sillier ways.
Edit: Hi Steve. It must be a quarter to midnight there; it is three quarters past here.
[edit: Directed at Steve. Jacob snuck in between. ]
That's eyeballing the tangent though. There's no automated method to get precise tangents in Illustrator. Smart guides are good, but they can also be incorrect at times.
What time is it over there, Scott?
3:50 pm. Why ?
Just to know how far west you are, Scott. You are right on forum time (PST).
Yup. About 1 hour from the Pacific. And not far from Cupertino or San Jose. Really close to Klammath.
Let me try again. In the picture, I have a circular arc that I've drawn with the arc tool. As you can see, it's a 90 degree arc. Is there a way to adjust the angle of the arc so that it would be enclosed within the two line segments that I've drawn. The application is to drawing figures for a mathematics text.
I don't see anything so "in the picture" and "as you see" mean very little.
You may be better off using the Ellipse tool to draw what you need, then use the Scissors tool to cut the shape and delete the sections you do not want.
The straight answer to your question is: Ridiculous as it seems, no. Illustrator's so-called Arc Tool is one of the lamest drawing tools I've ever seen in a drawing program. It is what it is, and nothing more. Practically useless.
The Round Corners effect is almost as absurd. On anything other than a 90 degree corner, it does not yield what anyone in his right mind would expect as the numerically specified "radius." Often, it's "rounded corners" are not even round.
Select the Arc, use the Scissor Tool to cut the path at the intersection... use the Direct Selection tool (White Arrow) to click the outer section, hit delete.
... Imagine two line segments with their ends meeting at a 45 degree angle. I want to to draw an arc inside that angle.
Turn the Smart Guides on, with The Arc tool move the cursor over one of the lines and when the Smart Guides say "path", click on it where you want the arc to start and drag holding Shift until the Smart Guides show a straight line indicating alignment with the intersection point of the lines, then release the mouse button to create the arc.
Take the Scissor tool move it over the intersection between arc and line and when the Smart Guides say "intersection" click there to cut the arc. Then make sure the unneeded part is selected and press Delete until it is gone.
If the arc is not oriented properly, while drawing it press X
If neither of the lines is perfectly horizontal or vertical, you will be better off to draw a circle with the Ellipse tool holding Shift and Alt to draw it from its center positioned at the intersection of the lines. Then cut the circle at the two intersection points with the lines and keep only the section you need (unselected part in the image below)
That's eyeballing the tangent though.
No it’s not. I rotate-copied the radii by 90° and snapped the endpoints of the copies to the ends of the radii (Smart Guides said "anchor").
I then scaled the tangents. Looks perfect even at huge zoom and with preview turned off.
And as James says, the Arc tool is almost totally useless. Use the Ellipse tool for starters.
Here's how I would do it in InDesign, you could probably also do this in Illustrator, but I could not get the rotation to anchor in the lower left corner. BTW, I believe there is an InDesign plug-in specifically for math text.
Draw a horizontal line, duplicate it. Draw a square white box the same size as your line on top of the line, group the line and box. Draw a circle and delete two of the anchor points to make an arc, send it to the back. Simply select the box and line group and rotate from the lower left corner to create any angle you want.