Guesstimating carbon content using the "Spark Test".

I've been using old machinists metal working files for the cutting edges on my laminated blades. Of course this begs the question; What's in this stuff anyway?

It has long been thought that files are made from 1095 (0.95% Carbon) high carbon steel. I really wish that I had some 1095 to compare against, haha! What I DO have is a handful of old files and a grinder (a camera, too), so I'll start with what I've got.




I don't profess any sort of expertise at this, in fact, rather the contrary. Mostly, they just look like sparks, right? I've looked at the stream of sparks shooting aft of the grinder many a time, but this time I figured that if I took some pictures, I might be able to see something interesting. I'm gonna warn you now, this is a very monotonous series of photos that is only going to be of interest to a few people (kind of like the rest of this blog, haha!

It was dark, and I was outside anyways.

The first time I tried the spark test on this Heller file, I knew that I had better start paying close attention. This is an old 8" file, of unknown age. It was old, rusty and dull when I got it, so I can't attest to its value as a file or how hard it is.

Usually the sparks that get thrown off of high carbon steel look like long, red streamers. This file was different.

These sparks are short, red, frilly little things. Also, extremely numerous and active. Notice the many forks and branches, ending with the smallest of explosions. It's like the 4th of July!


The cameras exposure time means that these photos make it look like there are more sparks than you would see in real life. That is one thing that was always throwing me off  when comparing my results to what I was finding online. An actual volume of 2/3 to 1/2 might be more accurate.

These sparks feel soft, delicate, fuzzy.



Next is an old 12" Heller. Again, old, rusty, and dull.

I have read that sometimes the carbon content might be slightly lower in a large file like this one, but that doesn't appear to be the case here.

In real life at least, these sparks look the same (to my eye, that is).

This picture is more accurate in terms of the volume of sparks that I was seeing.

Volume, length, color and intensity, all are indicative. If you apply more pressure to the grinder, you get a longer spark trail and maybe a more fully developed spark, but then it gets hard for me to take the picture, so....

Now for something that I am more familiar with, a Nicholson 4-in-hand file. I've bought a bunch of these in the past and have never been particularly thrilled with their longevity. There they are handy to keep in the toolbox though.

A very different spark here. 

A more intense yellow, a longer stream, and not as much "activity". Fewer sparks, but what is there looks to be intense. Many of the tracers end with a little burst and a branching fork.

Notice how the sparks are bouncing off the tin wall? The spark stream is nearly 4x longer than the Heller files showed.

These sparks feel harsh, coarse.

Now.

I am probably guilty of promoting the same information, right or wrong, as everything that I've found written on the net, but again, we work with the tools we have. 

It has been said that in the old days, Nicholson files were made from a special type of C1095 high carbon steel that had1.22%(+/-) carbon, but since the '80's have been made from plain 'ol 1095. I've seen a number of old technical reference books online that list files as having a carbon content of anywhere from 1.20%-1.50%, and made from the same type of steel that taps and dies are made from. Just the other day I was reading a technical paper that specified using Vallorbe (Swiss) files, made with a 1.22% carbon steel.

I can say with absolutely NO certainty that certain files are made using a particular type of steel. What I am comfortable stating, is that the spark pattern from these Nicholson files is significantly different from the spark pattern from these old Heller files. I would also say that these particular files are NOT overwhelmingly hard.

How about an old Simmons "Red tang"?

This is my current favorite, and an absolute brute when it comes to chewing through metal. It's age is anyone's guess, and it's still sharp, though certainly not anywhere close to being new.

The sparks are starting to look familiar now.

They look nearly identical to those of the Heller files.

Another Simmons Red tang, this time a triangular tapered saw file.

Same (or near enough).

Now for something interesting.....

This rasp sprays a very impressive stream of yellow/red sparks, but there is almost no branching, explosions dots or dashes. It shows just a stream of large tracers that only fork at the ends (if at all).

This is one of those cheap China files that are pitifully soft, and absolutely worthless at removing metal.

The length of the stream is telling as well. See how the sparks are rebounding off of the back wall?

All right, I am beginning to associate long, intense, yellow/red, boring looking sparks with really crappy files. I have a few of these (I know a bargain when I see it!), and they all behave in a similar fashion. In my entire stash of miscellaneous metal, the only thing that I've found that compares to this spark pattern is some dead soft, iron tie wire used for wrapping rebar bundles (a great source for free 1/4" iron, BTW, and easy as hell to straighten!).

I think that this may be a case of.... Case hardened steel.

How about another cheap China file? 

Here is one of those super hard, little detail files that I bought at Wal-Mart, and am always raving about.

Short-ish red sparks, very active, with a multitude of branching, forks, and explosions.

Last one (for now)....

An "Oregon" brand chainaw file.

Can anyone else see the similarity here, or is it just me, haha!

Interestingly enough, the "Oregon" files are made in Switzerland....

.... By Vallorbe.