How do you know when it is time to throw a set of knitting needles away?
I have many metal knitting needles that have the paint/finish worn off at the tip and the yarn will not slide over the needles easily. I also have some bambo needles that have a lot of gouges in the tip that catch the yarn and make it snag.
If they snag your yarn or the flaking might come off I’d say toss them.
I have a lot of older metal needles and while the coloring on the tips may have worn off a little, none to the point where they snag the yarn. For bamboo needles, you can take some fine sandpaper and smooth out the tips.
Can you try to polish up the metal ones with wax paper? (Thinking of sliding down a metal sliding board, we used to use wax paper to make it slippery-er.)
I use an emery board to smooth the tips of my bamboo needles. Sometimes they are just not pointy enough for me so I also refine the point when I feel the need.
Susan