Chisel making process
For chisels and drawknives we use cilium - manganese 9260 alloy spring steel. The first step is to heat a flat bar and to roll it down to the thickness of a chisel using a rolling mill. Rolling gives a good even thickness to the tool, and improves the structure and grain of the metal. Rolling is done while the steel billet is in a controlled temperature. In modern industry this process is known as Thermo - Mechanical Treatment (TMT). Secondly a socket is forged in the
chisel. This is done entirely by hand forging, using only the anvil, hand-held hammers and a steel cone for precision shaping and straightening of the socket. Finally the Northmen logo is stamped into the tool.
Heat treatment. Grinding. Sharpening
The chisel is slowly heated to 820 degrees Celsius and is held at that temperature for 10 minutes. During this time the structure of the steel transforms to become austenite. Now the chisel is quenched in mineral oil and the structure becomes martensite. Martensite is too hard and brittle, so to make it tougher the chisel is placed into an oven heated to 180 degrees Celsius and left for an hour. Now the tool has a Rockwell (HRC) hardness of 63 – 65 and is ready for the edge to be ground and sharpened.
At first the edge is profiled to 25 degree angle using a stone grinder. Then the chisel’s back is flattened on a belt grinder. The edge is sharpened on a whetstone and polished on a buffing wheel using green chrome oxide compound until it has a mirror glazed finish and razor sharp edge. Now the chisel is ready to be fitted with its own unique handle.
Each chisel’s handle is unique and made to fit by precisely copying the inner and outer dimensions of the chisel socket. The handle is hand turned on a lathe using wood-turning chisels and then sanded. Elm wood is very spiky so much care and attention must be taken during the sanding process. The final sanding for the handle is done using wood shavings left from the wood-turning process. These act as a very fine abrasive to give a better finish. The handle is now ready to be fitted to the socket. Using a chisel the handle is now shaped to perfectly fit the socket. Once the fit is good, polyurethane wood glue is applied and the handle is hammered down into the socket. After the handle has been fitted, linseed oil is applied, and it is waxed using a bees wax, linseed oil, and turpentine mixture. The chisel is now ready to go to its new owner.