How I make a Knife, Pt. 3

A good knife needs to be able to be sharp, to not dull after little use, and to not break under pressure. By using heating and cooling methods, I can manipulate the physical properties of the steel to meet these standards. First what I need to do, is harden the steel, so it can be used many times without dulling. To do this, I heated up the blade in the forge until it was a cherry red, the point at which steel, when touched against a magnet, does not stick. Once the entire blade was up to this temperature, I plunged, or quenched, the blade in motor oil.

When the blade is heated to that temperature, the iron atoms switch formation from small closed cube formations to larger open cube formations, allow carbon atoms, which had been floating around between the cubes, to float /inside/ the cubes. When the blade is shock cooled in the oil, the cubes shrink and close up too quickly for the carbon to float out, trapping the atoms inside the cubes. This makes the steel very rigid and hard, very hard to dull, but very brittle as well. To toughen the steel, I needed to heat the blade to around 400 degrees, which I did with the kitchen oven. This opens the cubes up a tiny bit, allowing a few carbon atoms to escape, lessening the pressure and making the blade much tougher, while still retaining it’s ability to hold an edge, that is, not dull.

The freshly quenched blade. At this point, I could break the blade with a few fingers

The process of heating the blade in the oven to toughen it is called tempering. I left it in the oven for three or four hours, giving the blade time to fully get to even heat, inside and out. The temperature at which I temper is determined by the amount of carbon in the blade, most files and rasps, like this one, having about .90% carbon by weight. While the blade tempered, I began working on the sheath. I first cut out the leather in the the shape I wanted, which I would later fold in half, using a paper cutout model as a size reference.

The leather will later be folded in half

I then use a metal stamp to make a decoration along the edge, quite easy to do as leather takes stamping very nicely.

I will later true up the edges of the leather

I set aside the leather for now, as the next step in sheathmaking requires the nearly finished knife.

After the blade finished tempering, I cooled it and roughly sanded away some of the black scale on a 220 belt. I then assembled the knife and used a cobalt alloy drill bit to drill through the handle and tang.

I took out the blade and put it in the clamp, bevel up, and began hand sanding. This is the most tedious and boring and taxing part of all of bladesmithing. I start with 220 grit sandpaper and work upwards, to 600, using a piece of wood for even pressure.

This can sometimes take hours to sand a knife, I’m not sure exactly how long as I tend to not be able to sense time well when bladesmithing. The worst part is taking out the small scratches left by the grinding belt, as they can be very deep and I’m removing all the steel within an inch radius with sandpaper to grind down even to the depth of that scratch. Anything I don’t get with the very first grit of sandpaper I can’t get out later.

Every one of these scratches has to be sanded out, it can sometimes take up to fifteen minutes just to take out one scratch. It helps if they are all in one area

Finally, I finished sanding, at 600 grit.

600 grit blade

I began to get ready for the final assembly of the blade. The pin material I had was a little too thick, so I had to grind it down to size. To get it evenly ground without any facets, I put the rod in the drill and ran it against the belt grinder, the rotations of the drill grinding the rod evenly on all sides, bringing it to perfect size for the hole.

As 36 is a very rough grit, it creates tiny ridges all around the pin, which will give the epoxy later a very good grip

I then mixed up the epoxy (using the pin; it gets the pin nice and covered) and dabbed a generous amount into the handle cavity.

The tape roll at the bottom is just so I could hold up the handle, take a photo, and hold the pin all at the same time

I also slathered a little on top of the wood so there would be no space between bolster and wood, in case the drilling had been a millimeter off. I slid the bolster onto the tang and the tang into the handle, and after pressing together and making sure the blade was straight, inserted the pin.

Freshly epoxied knife


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