How to add rounded edges at the intersection of multiple lines?

Question

I am looking for a way to add rounded edges at the intersection of multiple lines, like this :

But on a complex illustration with two or more lines intersecting at different angles, like this one :

I could always add these edges manually, but I would like to know if there is a workaround (or potentially an add-on) to keep the path as it is and be able to adjust the edge roundness etc.

Thanks in advance

Answer 1

To keep all as stroked paths make a collection of custom arrowheads which have the wanted roundings.

Alternatively you can insert the roundings as separate objects. Keep them in their own layer for easy access. Defining them as symbols makes global edits possible. That approach isn't practical, if you have plenty of non-vertical nor horizontal lines or you demand easy scalability and exact tangential fillets.

An example:

That was a group. If it's a closed shape, it can be adjusted with the direct selection tool to fit perfectly. Omitting the stroke increases tolerance, but makes the fillet allways non-tangential. An example:

NOTE: There's inserted a corner type anchor in the blue circle and there's rounded joints in stroke settings.

Perfect tangency needs dragging the handles on the lines:

I haven't it, but I believe Vector Scribe by Astute Graphics could make the separate object approach and also drawing generally much more streamlined. Check its demo.

Creating arrowheads can be found in Adobe's documentation, web tutorials and also from here How to create custom Arrowheads in Illustrator properly

Answer 2

I know you want to keep the lines editable but the way I'd do it doesn't really take that long so will probably do the job for you.

1. Create your line work on a layer (I'll keep it simple but of course you could use a set of layers)
2. Clone the layer
3. Select all the artwork on the cloned layer
4. Go to "Object" > "Expand..."
5. With everything on the cloned layer still selected, choose "unite" from the pathfinder panel
6. With this new merged shape selected, go to "Effect" > "Stylize" > "Round Corners"

With your original layer still visible you'll cover over the rounded ends to your lines and corners of squares etc.

Here's a quick demo to show the effect & layer set up:

When you make changes to the artwork on the original layer, just delete the cloned layer and repeat steps 3-6 (~5 seconds :-)

I hope that works for you.