Many years ago, we learned that a very large proportion of modern magnet wire is not coated with old-school enamel, but with some much tougher plastic. The only really reliable way to solder it was to dip the end in a solder pot first. Scraping works, but often takes several tries and risks nicking the wire. We've avoided it since. Sounds like a tool like this might help, but be aware of the issue.
