I've gone and bought myself one of those vintage Singer automatic zigzag attachments. A swiss made one, specifically. I did so with the knowledge that they would be more or less nothing but a gimmick.
Online, most people are very much in general agreement that these attachments are useless for actual work. They can't do edges properly and they aren't reliable when it comes to width of stitches. They're hard to steer and, as I said, pretty much a gimmick. The general consensus seems to be "they're fun, but buy a buttonholer instead".
Now, I disagree. At least these Swiss ones are perfectly usable as long as they're oiled up and adjusted. And this is the whole reason I'm making this post. Because maybe there's someone here on Lemmy who's been wondering about it.
The example picture above isn't an edge seam made after tens of hours of struggling. That's the second piece of test cloth I put under it after taking the thing out of the box. Is it perfect work? Definitely not, but it's the first time I tried to do an edge with it. This is a piece of cotton bedsheet cloth folded once, so pretty thin. I didn't press it, and I didn't think much when I did it. Since then I've used it on 4mm thick felt for edges. Works fine.
I just felt the need to say this. Maybe it's not that relevant to most people - hopefully it's useful to someone.
Thank you for coming to my LEMtalk.
My only other idea is have you tried changing needles?
I can't remember if I ever did it for this purpose honestly, I will try specifically that next time !
It's very easy for needles to be worn out without even being noticed. The tip can be worn and become hook shaped, the needle itself can be bent without it being visible to the naked eye. Changing them proactively can be a good practice.