A: That should not be a surprise. Any cutting tool will get duller with use. How long your files last depends on how you use them, and on what metals, and how you store them. Good quality, well-made files do last a longer time, given the same use, than poor-quality ones, and even more importantly, well-made ones will generally give you faster, more uniform cutting. But any cutting tool will dull over time with use.

Some files are harder than others, and they may last longer, especially with harder-to-file metals (platinum comes to mind here). It should be mentioned too, that paying a higher price does not always buy you the longest-lasting file. It generally means the most uniform and high quality cutting, and consistency from one file to the next. But just because a file is low in cost doesn’t mean it won’t also perform well. Some of my favorite and longest-lasting files were a cheap close-out special from Allcraft a few years ago: five bucks each for Polish-made hand files. The quality was as good or better than any Grobet file I’ve paid through the nose for, and they’re still going strong after at least five years of daily use.

I’ve also got some large coarse bastard-cut machine files that I got from MSC a couple decades ago, which are still cutting just fine, though they get only infrequent use. They’re good for some things, especially roughing in a wax model, but also for larger metal-filing jobs. Those puppies were Chinese-made, and were reasonably good—worth a lot more to me than the fifty cents each (in a bulk purchase of 50 assorted files) that they cost.

But if you’re really using nitric acid to clean your files, then I understand why they’re not lasting very long. Nitric acid etches the steel. Probably more quickly than it would attack the residue of metals caught in the teeth. That’s a quick way to destroy a file. If a file is already dull, you can get back a certain degree of sharpness with a careful acid etch. But it’s not as durable as the original cut teeth, and it certainly is not a way to routinely clean your files. Coarser files can be easily cleaned with a file card, which is a specially-made wire brush intended for exactly that use. Finer teeth files, too fine for a file card, can still be cleaned with a fine wire brush, or the finer rotary brushes used in flex shafts. This doesn’t always work well, but sometimes it will. Using the edge or corner of a scrap of copper or brass to stroke (or even strike) along the file teeth can remove much of the stuck residue, and a sharp pin will dig out stubborn bits. An ultrasonic cleaner is relatively effective, in some cases, at cleaning files with little work. Steam cleaners also can do a decent job. In both cases, be sure the file is carefully and fully dried so it doesn’t rust afterwards.

Some files, like the FB Dick yellow-tang files, are specially surface treated so metal residue doesn’t stick as much. They are especially marketed for platinum, but they’re good with other metals too. And they’re a bit harder, so they last well. You can also rub the teeth of a clean file with chalk or talc, which helps to prevent metal residue from sticking to the file as much. Make sure they’re stored so that each file doesn’t get rubbed or banged against the other files in storage, if you want the longest life from them.