Knife 49 – Hunter – EDC – Testing the Knife’s Hardness
- Blade – 4 3/4″
- Overall – 9″
- Scales – Stabilized Spalted Beech
- Handle Finish – Hand Rubbed Oil
Testing the Knife’s Hardness
Up to this point Testing the Knife’s Hardness has been to chop a hardwood scrap, roughly 2” x 2” by chopping at it as hard as I could. A used knife I had folded on the test and I couldn’t get it heat treated so it would not harden. I was still researching trying to find a better way without buying expensive equipment.
Then I stumbled on the “Brass Rod Test”. I think this test is a little more reliable and I’m not sure why it’s not documented with more knife makers writings.
I did find a couple different processes, both basically the same. On way is to just hold a brass rod in a vise, the other you mount it in a block of wood. I decided to mount a piece in a block of wood.
You don’t want the knife completely sharpened yet, but the edge geometry needs to be close to sharp. The idea is to fold the edge. If the edge returns to the original shape, the knife has the proper temper. If it folds and stays folded, it not hard enough. If it chips, it is too hard and should be run through a tempering cycle at a higher temperature than before.
Hold the knife at slightly more of an angle than the sharpening angle and put pressure on the edge enough that you see it fold. A light shining directly on it helps. As the edge folded, the light will change. Now drag the edge across the bar watching the fold slide. If the edge returns to its original geometry, you’re good to go finalize the sharpening. If the fold stays folded, the knife edge is not hard. If it chips, temper again at a higher temperature.
You can also force the edge to deform while checking the weight required to force a deform. If you can push at 30 pounds or so you know you’re ok. This is a good test once in a while, but until I bought the file set Hardness Testers on page 74 I did the test on every knife I made.
After a while, I began to become more interested in a serious test for hardness. I decided to order the “TTC 6 Piece Hardness Tester File Set”. This will allow me to get the hardness within the 60-65 Rockwell hardness which is ideal for a knife.
These file help measure Rockwell hardness. It’s measured as HRC, or Sometimes RC. An abbreviation for Rockwell Hardness measured on the C scale. The abbreviation usually appears after a number, e.g. 22 HRC. See: Rockwell C Hardness. Rockwell C Hardness is a designation of hardness, of steel or Corrosion Resistant Alloys.
A typical knife will usually be around 62RC, although some knives such as cleavers may be as low as 55 HRC as will machetes. Hatchet would also be 52 – 55RC. Some like a softer steel in the 54-56 RC range their knives. Softer steels require sharpening more often, but they are much easier to sharpen than harder steels. They are also less likely to chip. The edge is more likely to roll over, rather than chip, which is a much easier fix than a chipped blade.
To use the file to test my knives, I file the heat treated and tempered blade with the 55RC file. If it skates off, the blade is harder than 55RC. I then try the 60RC file. If this one almost bites or bites a little (a metal shaving shows up or there is a visible scratch) you are around 60RC. Moving up to the 65RC. This should skate over the steel. If it doesn’t another temper cycle may be in order.