Precise Arcs possible?

[Dachshund Daddy AJ]

I am trying to build an elipse to be precise to given location in my object. Being Very old school, I could do it witha compass, triangles, and a T-square. Is it possible to create an arc where the center of the arc is on one point (intersection) and draw the arc between to other points? I don't see a compass tool or I would use it. Thanks.

[Monika Gause]

can you please show a sketch of this?

[Dachshund Daddy AJ]

Gladly, Maam

[Jacob Bugge]

Dachshund Daddy,

As I (mis)understand it, you can replace all of the compass, triangles, and T-square, by the Ellipse Tool (flyout from the Rectangle Tool), and the Line Segment Tool, and first create the circle containing the arc, then cut the circle at the two desired end points of the arc and delete the rest of it.

https://helpx.adobe.com/illustrator/using/drawing-simple-lines-shapes.html

Smart Guides are your special friends friends for precision, telling you when you are within snapping distance, the word shown depending on how you have established the point, such as intersection if the point is the intersection between two paths.

This works for any three points defining a circle when you have already established them (shown in black), see the image set incorporating all the steps below:

1) With the Line Segment Tool ClickDrag between the middle point and each of the arc end points, snapping to both points (either direction works); shown in red;

2) Select each of the lines and rotate (a copy of) it by 90 degrees using Object>Transform>Rotate; shown in red;

3) If the rotated lines do not cross, scale either/each of them up uniformly using Object>Transform>Scale; the point where they cross is the centre of the circle, of course; shown in red;

4) With the Line Segment Tool ClickDrag between the centre of the circle and the middle point of the desired arc (or one of the others) snapping to both, then Click an empty spot on the Artboard with the Line Segment Tool which to reveal its length which is the radius of the circle, of course, then simply pres Ctrl/Cmd+C to copy it, then press Cancel; shown in blue;

5) Click with the Ellipse Tool on the Artboard and insert the copied radius from 4) in the Width field and add *2 in this field, then Click (the word) Height (not the field), then press OK; now you have the circle with the right diameter; shown in blue;

6) ClickDrag the Centre of the circle (Smart Guides say center) to snap it into its rightful place established in 3) (Smart Guides say intersection); now the circle ought to go through all three points; shown in blue;

7) With the Scissors Tool Click each of the desired arc end points, then with the normal Selection Tool Click the unwanted part of the circle and press Delete; shown in blue (dashed).

After that you can hide or delete all the objects no longer needed.

Click to get closer

Always keep backups of works in progress to fall back on.

In this connexion, after 7) you can click the right Arrow at the top right of the Layers palette and click Duplicate Layer, hide the old Layer with all the artwork (which you can fall back on) and remove the objects no longer needed in the new Layer.

If you get stuck, you can post a plain screenshot of what you have and describe the issue(s).

Unknown to most, it is quite easy to directly show images in posts, hence the following general suggestion:

Please show images by using the Insert Photos button (looks like moon over mountains) for each at the top of the reply box which makes everything appear right there in your post together with your text, rather than he more conspicuous Drag&drop attachment which requires helpers to open a new tab for each image and wait for its showing, then go back and forth; and if they just click it and wait for its showing and press the X to get back to the text, the image is gone so they have to open it again and wait to see it again.

Edit: I added a link to the Line Segment Tool.

[Dachshund Daddy AJ]

Thanks, Jacob. I'll give it a try.

[Jacob Bugge]

You are welcome, Daddy. I hope you will share your findings.

[Dachshund Daddy AJ]

Maybe I'm trying to be to critical of this drawing. Attatched is a copy of part of what I am trying to accomplish. It is going to be my rendition of a cam shaft. For starters, I attempted to follow the instructions posted by Jacob (thanks again for your effort). The train came off the tracks for me on the first instruction. When I select the line seg tool, and try to click & drag, all I'm getting is one line fron A to B ( refer to other posted drawing in previous post by Monika). So, I used elipse and rectangle to achieve what I have in the current drawing. I also can't clean up all the noise in the elipses. When I try Pathfinders or Direct Selection tool, some of the drawing is erased (parts that need to be visible).

Please understand that I am greener than grass with this program. A lot of the isometric drawings that I have done predate the computer! LOL! Yes, T-square, triangles, compass, and slide rule (sometimes). I await your further guidance, Obiwan; the force isn't strong with this one! Sorry for not catching on quicker.

[Doug A Roberts]

I was drawing a camshaft housing the other day, funnily enough:

I'm not sure where you need this arc. The only objects I needed really were ellipses transformed on to the isometric plane, and the cam lobes positioned along it. I used live paint to colour and obscure parts.

I use AxoTools to make my life easier (i.e. directly moving objects along isometric axes, creating extrusions), and a set of transform actions for each plane:

[Jacob Bugge]

Dachshund Daddy,

This is an adapted version of the instructions above, based on what you said, and your first image, so I have named the three points C, A, and B (from left to right), corresponding to the lower right corner if you tilt your head so A is at the top.

I have added a few of the old words rather than just say what to do with the new tools, including the express explanation of the steps.

I have also added more specifications of exactly how to perform some of the steps.

Obviously, as mentioned, the image set below, now with C/A/B, added, is (still) deliberatly loosely drawn.

Just in case, I have added a link to the Smart Guides,

https://helpx.adobe.com/illustrator/using/rulers-grids-guides-crop-marks.html

As mentioned, you can replace all of the compass, triangles, and T-square, by the Ellipse Tool (flyout from the Rectangle Tool), and the Line Segment Tool, and first create the circle containing the arc, then cut the circle at the two desired end points of the arc and delete the rest of it.

https://helpx.adobe.com/illustrator/using/drawing-simple-lines-shapes.html

Smart Guides are (still) your special friends friends for precision, telling you when you are within snapping distance, the word shown depending on how you have established the point, such as intersection if the point is the intersection between two paths.

Your A is at what looks like intersection between two crossing lines so it corresponds fully to the A here. B and C are where one line ends in another, so Smart Guides may say anchor.

This works for C/A/B defining the circle with its centre at the bottom, corresponding to a place down beyond the lower right corner in your image, and you have already established C/A/B (shown in black), see the image set incorporating all the steps below:

1) With the Line Segment Tool ClickDrag between C (snapping) and A (snapping) and between A (snapping) and B (snapping); shown in red with 1);

These are the basic lines for construction of the circle;

Next you need the normal/prependicular lines that meet/cross at the centre; instead of the compass, you just rotate copies of the lines from 1):

2) Select each of the lines from 1) and copy it in front of itself (Ctrl/Cmd+C+F), then rotate the copy by 90 degrees using Object>Transform>Rotate ; shown in red;

These are the the normal/prependicular lines, only too short, so you need to make them longer:

3) Since the rotated lines from 2) do not cross, scale each of them up uniformly using Object>Transform>Scale; the point where they cross is the centre of the circle, of course; also shown in red;

Now you have established the centre of the circle;

Next you need to establish the radius, and you can do that with the Line Segment Tool which directly measures the length:

4) With the Line Segment Tool ClickDrag between the centre of the circle from 3) and A (or B or C) snapping to both, then Click an empty spot on the Artboard with the Line Segment Tool to reveal its length which is the radius of the circle, of course, then simply pres Ctrl/Cmd+C to copy it, then press Cancel; shown in blue;

Now you have established the radius, next you need to establish the diameter in order to create the circle with the Ellipse Tool; obviously you need to multiply by 2:

5) Click with the Ellipse Tool on the Artboard and insert the copied radius from 4) in the Width field and add *2 in this field, then Click (the word) Height (not the field), then press OK; now you have the circle with the right diameter; shown in blue;

Now you have constructed the circle, next you need to bring its centre into place, namely the centre established in 3):

6) ClickDrag the Centre of the circle (Smart Guides say center) to snap it into its rightful place established in 3) (Smart Guides say intersection); now the circle ought to go through all three points; shown in blue;

Now you have the full circle, next you need to cut off the unwanted lower part so you only have the arc from C through A to B:

7) With the Scissors Tool Click each of the desired arc end points, then with the normal Selection Tool Click the unwanted part of the circle and press Delete; shown in blue (dashed).

After that you can hide or delete all the objects no longer needed.

Click to get closer

Edit: Or what Doug said.