Illustrator has this annoying behavior where it only generates a spline for a blend if one or more of the paths being blended are closed. My working method is such that I almost never generate closed paths, so this is super annoying.
There is a simple workaround, but it is annoying to do: swear, undo the blend, close the first path, make the blend, open the first path. You would think the swearing is optional but in practice I find it to be mandatory.
Today I got annoyed enough at this behavior to write a script to do it for me.
Throw this in your Illustrator scripts directory, and assign a hotkey to it via whatever method you choose – I used Alfred to bind command-alt-shift-b to a ‘launch apps/files’ action, which is the key I used to have assigned to object>blend>make. Now blends Just Work for me.
(And maybe go upvote the relevant uservoice issue if this annoys you too, I’d really rather have this choice something switchable in Illustrator without this kludgy workaround.)
Also, huge thanks to Past Me for setting up a workspace in Nova that points to my collection of Illustrator scripts and lets me hit command-R to run what I’m working on in Illustrator, damn. I stuffed an alias to Illustrator’s Javascript docs in there too so that Future Me has absolutely everything she needs to hack up a script without going looking.