types of files?

[mrwatch]

I have number of extra metal files that are worn or I will not use. Many may be Nicholson and a few are quality imports. It seems that a blade maker told me that their is a difference in the age "time period" for the quality of steel to make a fixed blade. I do have a wet wheel grinder. 3-4 inch blade, what thickness should I consider and choise of a file?
Thanks, Bob

[Gunsil]

I believe if you wish to make a knife from an old file you will have to anneal the metal first, then shape and grind your blade/knife and then re-harden and temper it. Files as they are are too hard and brittle to be good knives. It is a fallacy that blacksmiths made knives from files in the old days, like the 1700s and early 1800s. Back then a file was worth way more than a knife and files can also be annealed and teeth re-cut. The only true quality imported files are the Swiss ones, all the Japanese/Chinese ones are not so good. Any Nicholson will be plenty good for a knife.

In case you don't know, annealing is a heat process to soften metals. One simply heats the metal until an even red hot and then lets it cool in the air. This also "relaxes" the molecules so the metal becomes more malleable and less brittle. The metal also becomes easier to grind and less likely to burn even though you have a water wheel. After creating your blade one then has to harden and temper the steel to make it hard but not too hard and have more strength against breaking. If you take a good file and put sideways pressure on it it will snap easily without flexing, not a trait one likes on knives.

To do a simple harden and temper one again heats the metal to red hot but then quenches it by dropping it into a bucket of oil which should contain at least a couple of gallons and have a mesh above the bottom so the blade doesn't sit on the bottom. You can use old discarded motor oil, it will stink up the place but it can be had for free. To do a simple temper, the blade needs to be fully sanded and polished and then put in an oven around 500 degrees until the metal turns a nice even straw yellow color. You can buff off the yellow color when cooled. This is backyard knifemaking and it works. Metal will be hard enough to take and hold a good edge but not so hard as to snap with use or dropping.

[Bill DeShivs]

Files are already hardened, so tempering is all that is necessary.
If you are using a wet grinder, there is little chance you will overheat the steel. You can temper before grinding to make it easier.
About 1/8" is a good thickness for a 3-4" blade.