Hand Tools Archive

Re: A follow up on file steel...(squash knives)

In my very brief and not entirely successful foray into knife making 30 some years ago as a mid/late-teenager with little understanding of how things worked and only having access to a doug-fir bark fired forge... I, almost certainly inadvertently, made one of the best knives I've ever used out of an old file.

I'll recap my process here, not under any implication that its particularily valuable in and of itself but perhaps it might be interesting to see if there are parts I was completely off line on.

First I annealed the file by doing the traditional cherry red and then slow cool in the forge. Basically at the end of the day after repairing some hay rake teeth (and probably something else) I heated it all up then just kind of collapsed the fire in on the steel and left it overnight. I think this is probably slower than the cool-in-ashes method but I don't think it probably matters to much.

Next I ground off all of the file teeth. My basis for this was my dad claimed that it was less likely to have flaws carry through the steel from the sharp gullets on the file teeth. In theory this minimizes cracking potential. I don't actually know about this part but it sounded good so... I went with it.

The piece was then hammer forged to rough shape. This involved cutting the end of the file off on the hardy, and squaring up the tang a bit and putting a bit of a "sharp" (ish) tip on it (I generally "boil a deer horn tip until the inside is soft and then drive the tang into it" trick for a handle back then.. minimizes the amount of steel needed). The blade was hammer formed to "pretty close" to shape modulous the hollow grinding. I forged a bit of a sharp edge at the transition between the tang and the blade for the bolster to rest on, that was crisped up with a file after the next annealing step.

Another annealing step to take out all of the hammer stress and soften it to make it easy to grind.

Grind to basically finished shape leaving the edge a bit thick. Also do a reasonable rough polish.

Heat to cherry, quench briefly (until it just stops sizzling). Quickly pull out of the oil, hit it with a file to show the colors, watch the colors run until you're just about pale straw at the edge then plunge back into the oil for final quench. This will end up with a somewhat differentially hardened blade with the back a smidge softer that the edge hardened just a bit under straw (you loose a little between observation and final quench). At this point I'm not sure I wouldn't just quench fully and then post heat treat to get the right temper... My success rate at gettting a good blade past this point was kind of dissapointing. When its done just right though it makes a really nice blade.

Do the final grind being careful to not pull the temper and then polish and sharpen. Assemble the handle.

Standard test was to put a soft piece of 1/4" steel wire on a chopping block, rest the blade on the wire, and then wack the back of the blade with a 2x4. repeat along the blade every 1/2" or so. If the blade bent or chipped it wasn't good otherwise it was deemed ok.

The one blade that came out REALLY GOOD from this was used to skin a cow entirely in one pass with no sharpening and was still super crispy sharp at the end. Now that might not seem like a big deal but basically every other knife we ever used for butchering needed to be sharpened at least twice for a large animal.

This knife rode on my belt for some years until the hold down came loose and it bounced out of its sheath somewhere along a mountainside (I know the mountain, I know the trail, never found the knife).

I also had a couple that shattered on testing and a couple that I couldn't seem to get to harden very well either. There seemed to be some variance in steel quality/composition even back then based on spark tests and general post-working behavior. I certainly didn't know enough to quanitify it further back then and pretty surely still don't now.

Not sure what this tells anyone other than "yeah some files definitely have really good steel" and "here's one way that worked a couple of times" for whatever that's worth.

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