I have two shapes, in this case red and dark blue circles (for clarity), that I want smoothly connected by a tangent line and eventually united into a single, monocolor shape path.

red and dark blue circle

I am using the 'Tangent Line Tool' from the Astute Graphics SubScribe v2 plugin to create my tangent line between my two shapes (I've also tried this manually and using another free Common Tangents plugin, and I run into the same issue.)

So, I create my tangent line (green with thick stroke for illustrative purposes) between the red circle and dark blue circle. I've highlighted the endpoints of the line in light blue. So far so good, outline looks pretty precise to the naked eye and is the tangent I want.

red circle and dark blue circle connected by green tangent line

In order to unite the shapes using the pathfinder, I'll need to turn the tangent line into a shape, it can't just be a line, so I do that. Leaving the original endpoints of the tangent line exactly where they were, I connect the end points of the tangent line by making two new points, thereby creating an arbitrary square shape with the Pen Tool.

green tangent line made into shape via Pen tool

I zoom in as much as I can on the tangent line point that overlaps with the red circle; so far all the points are where I left them and look OK.

zoomed in on tangent point

Now here's where my problem arises. I hit Unite in the pathfinder to join the red circle with my green square, expecting Illustrator to make a nice clean monocolored shape leaving my points exactly where they were, then BAM, the shapes unite but Illustrator has for some reason shifted the shapes before uniting/created two points and nudged them away from the original point position, dirtying up my nice clean shape path. See the issue highlighted below in light blue circle.

enter image description here

Using the Shape Builder Tool also results in the same problem.

Snap to grid, snap to pixel grid, snap to point, etc. are all off, and it doesn't seem to matter whether I'm working in a web or print doc, or in pixels, points, or otherwise.

I know I could just fill in the tangent shape the same color as the entire shape I'm making and leave things overlapping, but I won't have a nice single, clean shape path.

Is there any way to get around this? Any insight is highly appreciated.

  • You can tighten the tolerance of pathfinder in the option under the hamburger menu.
    – joojaa
    Jun 18, 2020 at 14:24
  • @joojaa Thank you for pointing this out! Why it's not set at the most precise setting by default seems a bit ridiculous, but I went and changed the setting to the smallest value possible, 0.001pt, and checked the 'Remove Redundant Points' checkbox. It's still not quite perfect, though. The points are a lot closer together than they were before, but there is still more than one point, so it's not a perfectly clean shape even with those changes.
    – Denjin-K
    Jun 18, 2020 at 15:21
  • Im thinking this may in fact be the circle approximation error.I dont use adobe CC but seem to me adobe tries to implement underlying primitves.... Try adding a point to the circle before this op. Anyway the reason its not set to highest settings is that it makes more messy objects. For most graphic design uses its preferable to be clean than perfect. Anyway in general all illustrator defaults are totally retarded you need to spend 5 minustes setting defaults when you open a vanillia illustrator. SO retarded in fact that i feel its impossible to learn illustrator with the defaults.
    – joojaa
    Jun 18, 2020 at 16:12
  • What about deleting the extra anchor points with the removal tool manually or by applying Object > Path > Simplify?
    – user82991
    Jun 19, 2020 at 6:42
  • @user287001 Yes, I'm aware I can do those things, was just hoping someone knew how to resolve the issue without having to resort to doing so. i.e. Would prefer Illustrator not shift the shapes/create the extra erroneous points requiring me to delete them in the first place.
    – Denjin-K
    Jun 20, 2020 at 7:48

2 Answers 2


Either your rectangle is faulty or your Illustrator version makes errors. Here's my attempt. I use legacy stuff.

enter image description here

In the left there's a circle as Illustrator draws it with the ellipse tool. It has got no transforms after it was drawn.

The rectangle is drawn with the rectangle tool and rotated around the center of the circle. Inside the red circle the joint should be tangential and it looks tangential in the outline view mode with the biggest zoom.

In the right the rectangle and the circle are united with pathfiner panel unite. Max zoom shows no fault in tangency.

It's possible that continuing an existing curve with the pen spoils it. Lock your old items and draw by clicking with the pen a brand new rectangle or drag the cornerpoints of an ordinary rectangle to the right places. This way the continuing with the pen error possibility is eliminated.

  • Bezier corcles arent actually circular. But since adobe is trying to be more svg compilant maybe new illustrators actually have true circles which then turn into approximations once expanded
    – joojaa
    Jun 20, 2020 at 11:32
  • @joojaa doing my movements in Inkscape really converts the SVG circle and rectangle to paths, but the result is still perfect. Of course, it doesn't reveal how Illustrator could be made to do the same.
    – user82991
    Jun 20, 2020 at 11:51
  • Yeah... Anyway im not usin illustrator CC because adobe keeps onsering new bugs that i can not overcome
    – joojaa
    Jun 20, 2020 at 12:32
  • @joojaa can you give a good text for the dog in the next image dropbox.com/s/1c2rbxpk4b2obcv/InAdobe.jpg?dl=0 Something which describes how those new software "properties" are born .
    – user82991
    Jun 20, 2020 at 14:26
  • @user287001 Could you still do this cleanly between shapes that are: of arbitrary size, distance and angle, and that weren't already centered with each other from the get go, for example as with the circles I used in my original question?
    – Denjin-K
    Jun 24, 2020 at 7:35

After furiously digging through hundreds of online posts, articles and queries with similar-but-not-quite-the-same issues, I still couldn't find an answer that effectively resolved this particular problem. I explored every option I could think of, and after several attempts (and a possible concussion resulting from repeatedly bashing my head against my desk), I finally landed on a one-click workaround that results in a nice clean shape that doesn't require one to perform any additional unnecessary steps like: deleting erroneous points, nudging things around, averaging the location of points, simplifying the path, starting with shapes that are already the same size/at 45° or 90° angles, or using shapes that started centered and rotated around the center of one another.

As far as I can tell, this is a problem inherent to Illustrator that surfaces whenever you are attempting to unite tangent lines between shapes that are of different size, arbitrary distance, result in lines that aren't at a 45° or 90° angle, AND/OR weren't created centered and rotated around the center of one another. If one or more of the aforementioned statements is true, no matter how dead-on these scripts/plugins are when they create the tangent lines, the result will always end in Illustrator creating a shape that gets nudged and has erroneous anchor points when you click Unite.

Now for the solution: In the scenario where you are trying to create a clean shape from tangent lines joining shapes that don't meet ALL of the requirements above, the ONLY way I've found that works is to edit a default value of Astute Graphics' SubScribe Tangent Line Tool. With the tool selected, hit Enter/Return to bring up its Preferences and check the 'Add Points to Existing Paths' checkbox. Once you've done that, you can create the tangent lines between the two existing shapes as usual. Just join the end points of the tangent lines to create a quadrilateral (using the Pen Tool or Ctrl/⌘+J, either way works fine). Now click Unite and you're golden, no erroneous points, no shifting of shapes, everything is as it should be.

Tangent Line Tool Preferences

Sadly, this means you can't use the free Common Tangents script for this scenario, but at least there is some way around it.

  • I wouldnt say its inherent but adding a point does indeed combat tearing. Anyway whats the exact version of illustrator you are using as i cant reproduce this on my version.
    – joojaa
    Jun 24, 2020 at 10:55
  • @joojaa Was using the latest version available on Creative Cloud; updated to 24.2 today and I can still reproduce exactly as before. Happy to record my screen if you'd like. It's pretty infuriating.
    – Denjin-K
    Jun 24, 2020 at 12:08
  • @joojaa what really drives me up the wall is that the anchor points at the ends of the tangent lines are in the EXACT same locations that they are when 'Add Points to Existing Paths" is turned off; when it's on, it just creates a duplicate set of anchor points in the same locations in the path. All told, having that setting checked is really just creating what feels like extraneous points, but it works, so I'm rolling with it.
    – Denjin-K
    Jun 24, 2020 at 12:50
  • Well adobe is in a bit of ditch here they can not do all the changes needed in one go so they are incrementally changing foundations which to you translates as bugs untill they have enough of tgem to roll put a paradigm change. Or then not as there is a danger that the leadership changes before that.
    – joojaa
    Jun 24, 2020 at 14:42

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