Perfect Half Circle

[Mark_McFarland@adobeforums.com]

I hate to ask such a basic question, but I need to make a series of half circles, all sharing the same center point, but each of the circles has a slightly smaller radius. Could anyone help me with this basic problem? Thank you very much in advance.

[Gary_Newman@adobeforums.com]

You're right - it's basic.

Get the Ellipse tool. Click on your page. In the diaog that appears, type in the width and height of your largest circle and hit OK. A circle appears. With it still selected, click the same Ellipse tool on the circle's center point, and enter a new width and height for the next smaller circle. Repeat for all the remaining circles you need. Now get the Direct Select tool (white arrow). Beginning just outside, and to the left of, the the biggest circle's top anchor point, drag down until you are just inside, and to the right of, the smallest circle's top anchor point. This will select just those top anchors in all the circles. Delete. ;-)

[John_Kallios@adobeforums.com]

Someone will be along soon to mention using a blend for the stepping of the half-circles. But, it will not be me. (and Gary already knows this)

Walk before you run and all that jazz type of thing. :)

[p1kuo@adobeforums.com]

I usually just use the scale tool and then hold down alt to make a copy and shift to keep it constrained. the scale tool's default starts at the objects center... it's not as percise though..

[Wade_Zimmerman@adobeforums.com]

What Jk is suggesting is that you make the largest and smallest circles the way Gary
suggested and the go to Object>Blend>Blend Options and choose the the number of steps you want in between the largest and smallest half circle the go to Object>Blend> Make or Command+Option+B and there you are you can expand this if need be.

[Gary_Newman@adobeforums.com]

These alternative methods are fine, but not if the half-circles need to have specific radii. Unless, of course, those radii happen to coincide with those that would result from those methods.

[Mark_McFarland@adobeforums.com]

I hate to waste even more of your time, but I can't seem to get the circles after the first to appear with the same center point. I followed the instructions to the letter, and my second circle appears off to the side. Is there a trick to this?

[Doug_Katz@adobeforums.com]

Mark, do you need these half-circles to have SPECIFIC radii, or need they only be progressively smaller?

If the latter, then after drawing your FIRST circle, make the Scale tool active and option-drag it from outside your circle toward its centerpoint. The option key will create a copy of your first circle with the exact same center point. Now you can blend the two as instructed in an earlier post.

If you want the dialog box that Gary recommended so you can define precise measurements for each successive circle, then option-click the center point of the first circle with the ellipse tool. With the option key pressed the circle you specify will be drawn from the center outward from the point you click.

[Wade_Zimmerman@adobeforums.com]

Doesn't seem to work but you can align them with the align palette align horizontally centered then vertically centered.

[Doug_Katz@adobeforums.com]

Huh? Which doesn't work, Wade?

By the way, Mark, if you use the option-click with the ellipse tool method (to get the dialog), turn on smart guides (command-u). Then you'll know by visual feedback when you're right over the existing circle's center point.

[Gary_Newman@adobeforums.com]

To get them all from the same center point, be sure you have Snap to Point (View menu) turned on. Also, in Doug's instruction for scaling proportionally, be sure to drag diagonally toward the center point. If you drag horizontally or vertically, you'll compress your circle in that direction only, into an ellipse.

[Wade_Zimmerman@adobeforums.com]

[John_Kallios@adobeforums.com]

There are many ways to accomplish this. Here is another variant.

Select elipse tool (L)

Click on artboard. (not click and drag)

Enter desired diameter for width and height for small circle. (example a .5" diameter)

Select left anchor point with direct selection tool (white arrow) and delete.

Select top anchor point and shift-select bottom anchor point with direct selection tool. (So both top and bottom anchors are selected at the same time)

Object>Path>Join (command+J)

You now have a semi-circle with radius of .25".

Select with black arrow and copy and paste in front. (command+c and command+f)

Object>transform>scale to 400%. (the pasted semi-circle has a radius now of 1")

Select both and in Align palette, click on the horizontal align left button.

Object>Blend>Blend options: Switch to specific steps and enter 5.

Select both semi-circles and Object>Blend>Make.

Select the elements again and Object expand (uncheck stroke)

You now have semi-circles that are aligned by the radius's starting point that are .125" different in radius length.

Just one of many, many ways.

[Mark_McFarland@adobeforums.com]

I hate to ask yet another basic question, but now that I can make the perfect half circles, I realize that I didn't foresee another problem. What I need of these semi-circles is the line itself with a transparent interior. I see how to transform the color and transparency of the interior of my circles, but how do I change the color and width of the line itself?

Thank you all so much for your generous help. I am about to send an article off to my editor, and he wants everything camera-ready. The only thing I wasn't able to do had to do with these half circles. Your help has been invaluable!

[David_Sansom@adobeforums.com]

Select the line, press X on the keyboard to to make the Stroke option in the Toolbox active, choose a colour from the Colour palette.
Change the thickness using the Stroke palette.

[Wade_Zimmerman@adobeforums.com]

And Mark that's it you get one more basic question and we expect you to be expert by now. So after that it is only advanced questions! 8)

[James_E._Talmage@adobeforums.com]

"Someone will be along soon to mention using a blend for the stepping of the half-circles. But...Walk before you run and all that jazz..."

"...but I can't seem to get the circles after the first to appear with the same center point."

To draw the concentric circles quick & easy:

Get the Polar Grid Tool.

ClickDrag in the document (don't worry about it being perfectly circular at this point).

Before mouseup, Press the left-arrow key untl all the radial dividers are gone, Press up/down arrow keys for the number of desired circles. After getting the number of circles you want, keep holding the mouse down and then...

....press Shift (this constrains to a circle), then mouseup.

Note that this also works for concentric ellipses. And you can make the spacing progressively tighter/looser toward the center by pressing X and C keys during mousedown.

JET

[Gary_Newman@adobeforums.com]

I love it when somebody comes along and posts an even more elegant method for doing something. So here's an addendum to JET's excellent idea.

Get the Polar Grid tool and Option-click on the artboard. Fill in the form.

;-)

[James_E._Talmage@adobeforums.com]

"Option-click on the artboard."

Don't you mean just Click on the artboard? (Or Double-Click the tool?)

On Windows, AltClick just draws a Polar Grid using the current settings. Clicking invokes the dialog. I wouldn't think that would be inverted between platforms, but...?

JET

[Gary_Newman@adobeforums.com]

That's AI 10. In CS clicking will put the specified grid's upper left bounding box corner at the click location (AI 10 uses the grid's bottom left corner). Option-clicking brings up the dialog, and puts the grid's center point on the click location.