Hand Tools Archive

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

david weaver
..last year, or maybe two years ago, I asked if files were high carbon steel all the way through or if they were case hardened.

I got various answers when I asked that question. Since then, I've made about 10 knives that I call squash knives out of files (heat a used file, squash it with a hammer, refine the profile with a grinder, files or belt grinder and then quench, temper and sharpen).

These turn out to be dandy little knives. whatever they are, if you treat them as you would O1, they hold up really well to things you'd use a small knife for (marking, cutting up boxes, etc). I have a distaste for utility knives because they're bulky and the blades are often soft, even modern ones.

These squash knives have taken over everything I do in the garage (cutting down cardboard boxes, etc, cutting package labels out of printed paper, whatever - and marking, of course) because the blades are thin and small and you can wrap the rest of the handle if you need a better hold, but they just slip through everything because of the blade profile.

I sharpen them with a gray deburring wheel and then a hard buff, and then once in a great while, take them to a norton IM 313 (the best knife profiling device in the world) and restore the edge to straight of it's getting a little out of whack).

Not a single one has exhibited behavior that is untoward (low carbon or any other kind of flaw), and i have no clue why that is because I don't know what they are other than that it's clear they're enough high carbon steel and little enough alloy that they work really well.

I've since smashed and ground some larger files into double hollow knives to keep the profile thin, and they also work a treat, but anything larger than small, high carbon and hammering into shape is heavy work.

Yesterday, I was off center (following up vacation and a busy work week and a bunch of chores, just out of gas) and didn't feel like starting anything gainful that required too much thinking, so I made three of them (think equivalent type project to turners saying they turn pens when they're feeling a little uninspired because you can just turn a couple and be done with it). It takes about an hour for me to make, grind, and treat three.

What i noticed was one of these was with the width waste off of shootenstein's iron stock (presco O1, fantastic stuff), and to my surprise, very light straw O1 steel at high hardness still likes to hold a little bit of wire edge. If I can find some large triangular vintage files, I'm inclined at this point to think again about making chisels - hammer down the apex, grind the back annealed, reharden and then grind out a profile.

I expected that the first couple of these would be marginal or unusable, but due to their lack of conviction with the wire edge, and lack of deflection in use cutting up boxes, etc (the heavier file knife is fine to profile wood), they're a treat to use and the O1 knife comes in second.

Seemingly heresy to us because O1 is often the plainest steel offered now at high hardness, but I had the same experience with razors - honing for someone who was a good customer of mine when I was selling japanese natural stones. He'd bought some new Hart razors and I just didn't find them very nice to hone. They're O1, and spec hardness, but they want to hold on to just a little bit of a wire edge, and at 18 or so degrees of total bevel angle, that is a toxic habit. When it comes off, they're damaged.

As far as chisels go, I've given up figuring out how to make an integral bolster, so I think I'm going to make a tapered tang and file a tapered hole into a bolster to fit and heat it and just tap it into place as far as it will go.

I am also tempted at this point to locate good quality 1095 and see what it will do when it's only lightly tempered. We don't usually see 1095 that hard - it's in pocket knives or something else where it will hold a wire edge just because of it's lower spec hardness, but the way the smash knives hold no wire edge and then get no deflection in use is....well, something I've only seen in japanese knives.

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