Sewing other fabrics onto stretchy fabrics Sewing Machines Parts and Sales in Los Angeles

I'm making some finishing touches to altering this character's top. I'm having trouble with the cups, though. I have them all ready to go, I just can't figure out how to prepare to sew it on in place.

The trim was the easiest because I didn't have to measure where it had to go–I just sewed it around the opening in the back and top. It's just the cups that are difficult for me.

Is there an alternative to having me wear the knit top, pinning the cups to my boobs (and probably poke myself numerous times in the process), and trying to carefully take it off without poking myself? Probably a dumb question.