Your machine needle is a vital, but often neglected, part of your sewing arsenal, at least by most of you. You know who you are! Not really picking on you, but most people use a needle far too long before changing it.
It’s a good question, because it depends a great deal on what you’ve been doing. As a general rule, you should change your needle about every 4 to 6 bobbins, more often if you are sewing heavy or rough fabrics, using metallic or other rough threads, or if you get adhesive on the needle shank, discard that needle. Certainly, if you’re having problems, try changing the needle as part of the discovery process.
When your machine comes in for service or repair, I change the needle before the machine even gets plugged in. That way I know the needle is good. The needle is also used for several touchy machine adjustments, which makes it even more important to know its status.
Make sure you buy needles from a trusted source. I’ve found bad quality needles in some of the respected European brands recently, probably because they’re being sourced from inexpensive third parties. For sure, stay away from the “box” stores when you buy needles. (That goes for thread, too, but that’s another story.)
When you remove a needle, for whatever reason, discard it right then. If it goes back into the little box, it’ll look just like a brand-new one!
In the shop, I keep a plastic pill bottle with a small hole in the top, where I can drop a used needle. That way it’s gone, and can’t hurt anyone. If you bring me your empty bottle, I’ll be happy to drill the hole for you, by the way. Changing your needle often is an inexpensive way to help keep your sewing experience a good one!
As an added footnote: On older machines, it may be possible to put the needle in backwards, so remember to watch for that on your “mature” machine! On all machines, make sure the needle is all the way up in the needle bar when you tighten the clamp that holds it in.