I had a terrible time make gathers recently and decided to find a way of making it easier so I wouldn't lose any more of my mind.
I tried various things and what I found that worked best was to use heavy thread specifically Uphostery thread that I found at Joann's.
The brand I used is Coats - extra strong.
What a difference!
I wound it on the bobbin (only) and it fed through just fine. I wasn't sure if it was too thick at first.
I sewed a straight stitch and used different lengths to see if that might make a difference (didn't notice one) and it gathered up instantly by pulling on the bobbing thread.
It was a miracle!
I have horrible memories of breaking threads and having it all fall apart so I avoided anything with gathers.
Gosh I wish I knew this long ago...
THis thread works well if you run a zigzag stitch over it rather than putting it in the bobbin. This looks good on home dec stuff. I don't use it when I want "tiny delicate" gathers - to get those you need to do a straight stitch.