My 15-91 is my all time favorite machine, but I have experienced the same as you with some of my bobbins. I think my problem is the groove in the bobbin is too shallow to stay engaged. If you can find vintage bobbins, that would most likely solve the problem. Sew Classic now advises using their plastic bobbins for the 15-91. I have some, they work fine, but it almost feels wrong somehow to put a plastic bobbin in my beautiful vintage machine... I know, l'm nuts! There's just something about a nice, metal vintage bobbin...
Joe mentioned a great solution to reduce frustration - when you find a bobbin that works, keep it with that machine. I think I will start sorting which ones work and find a different use for the defective ones...

I looked at mine again, and it may be that you can put in a shim where the lever attaches to the bracket to shift that lever to the right. You'd have take the winder off and see if that is possible.

Bobbin and winder... Excuse the filthy machine, please.


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Here's another bobbin picture that isn't focused on the sewing table.

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Addiction, thank the help. I will surely try the paper method out.

Macybaby, thank you for this suggestion. I may try it out.

DKuehn, I am so grateful you fulfilled my request for pictures. The post on my machine is worn down compared to yours and my bobbin has a different shaped hole from analyzing the difference in yours and my bobbins. I may need to get a new post part and a new bobbin, lol.

Thanks to everyone for their time helping me and offering suggestions

I have a 15-88 and all I use are the multi-hole class 15 bobbins. I did have trouble winding bobbins until I fine-tuned the bobbin winder. I still have to put a bit of finger pressure on the winder while it's running. The 15-91 balance wheel is a bit different from the 15-88 so I won't tell you how to release your bobbin winder, but it's a step I must make on the 15-88.

I'm guessing if you put that bobbin against the pin on the winder, it's not fully seating. The other thing you can do is if you or someone you know has a dremel - you should be able to resize the slot on the bobbins so they hold better. I've dremeled lots of stuff out when I've been in a pinch including DBx1 needles to fit class 12 machines. Just remove all of the filings before using the bobbin after dremeling.