There is a simple way to test knife sharpness and toughness that compares your blade to a standard. It is called ‘The Brass Rod Test.’
We are swiping the edge across a brass rod. I use a brazing rod. I count how many swipes I get and am still able to cut newspaper without it tearing. I begin by putting a good edge on the blade, maybe not a perfect or the best edge, just a standard uniform consistent edge on all knives I compare. I do this myself by using a 600 grit belt on my sander. This produces an edge I feel the average person would call sharp. It will shave hair. Now the blade is ready.
I use a brass brazing rod, usually 1/8th. Be sure it is brass and not a specialty harder bronze, or if so , understand this effects comparing your numbers to what someone else is doing. Swipe the full length of the blade. A pressure as if you were slicing bread. Not hard, but more than just the weight of the blade. Swipe as if you were trying to cut the rod in half. Count a forward stoke and a backstroke. I go at least 30 swipes before running the edge across newspaper held in the other hand.
A standard factory blade like Buck, Gerber, Leatherman, will usually get 30 to 50 strokes before tearing the paper instead of cutting. Just as some numbers to begin comparing with. I began getting 100 stokes when I first started treating steel, but soon got to 200 and use this as my own minimum requirement on a working knife. I sometimes get 400 and sometimes get over this and simply quit. I talk to just a couple of other knife makers who generally get 300 stokes on a good custom blade they turn out. This could be your goal.
So if you are a new knife maker, these numbers get you in the ballpark of what to expect. Take note, it is easy to get numbers better than normal factory, twice to three times as good at edge holding.
There are other factors to a good blade. I do a quick cheap hardness test by running a file across the edge as if I were using the file to sharpen. There is a set of hardness test files if you like. I began with this set but any file tells me what I need to know. With practice it is not hard to tell by sound, feel, and look ‘where you are,’ on the harness scale. You could learn by using the file on a known blade harness. Just a light drag is all that is needed. I like the file to slide off with a high hiss sound, leaving no mark. This means the edge is close to as hard as a file. In the 60-62 park. Actually a huge difference between 60 and 62, but this gets you a rough idea. If the file leaves a mark, makes a flat shhhhh, instead of ssssss, this usually indicates under 58 Rockwell. Possibly be ok, but at least know. Some knives you’d want to be able to sharpen with a file. Much depends on kind of steal and type of knife. If the file cuts deep and digs in, this indicates maybe 55 rockwell and this is usually getting into ‘did not take the heat treatment correctly.’ Keep an eye working the length of the blade and see if it is consistent. Do both sides as well. If not consistent, this could mean the blade was not evenly hot in the heat process or the steel has some inconstancies, internal stress. I want to control the edge and have the tip not as hard so tip less likely to break if dropped or stabbed into stuff.
I use a brass brazing rod, usually 1/8th. Be sure it is brass and not a specialty harder bronze, or if so , understand this effects comparing your numbers to what someone else is doing. Swipe the full length of the blade. A pressure as if you were slicing bread. Not hard, but more than just the weight of the blade. Swipe as if you were trying to cut the rod in half. Count a forward stoke and a backstroke. I go at least 30 swipes before running the edge across newspaper held in the other hand.
A standard factory blade like Buck, Gerber, Leatherman, will usually get 30 to 50 strokes before tearing the paper instead of cutting. Just as some numbers to begin comparing with. I began getting 100 stokes when I first started treating steel, but soon got to 200 and use this as my own minimum requirement on a working knife. I sometimes get 400 and sometimes get over this and simply quit. I talk to just a couple of other knife makers who generally get 300 stokes on a good custom blade they turn out. This could be your goal.
So if you are a new knife maker, these numbers get you in the ballpark of what to expect. Take note, it is easy to get numbers better than normal factory, twice to three times as good at edge holding.
There are other factors to a good blade. I do a quick cheap hardness test by running a file across the edge as if I were using the file to sharpen. There is a set of hardness test files if you like. I began with this set but any file tells me what I need to know. With practice it is not hard to tell by sound, feel, and look ‘where you are,’ on the harness scale. You could learn by using the file on a known blade harness. Just a light drag is all that is needed. I like the file to slide off with a high hiss sound, leaving no mark. This means the edge is close to as hard as a file. In the 60-62 park. Actually a huge difference between 60 and 62, but this gets you a rough idea. If the file leaves a mark, makes a flat shhhhh, instead of ssssss, this usually indicates under 58 Rockwell. Possibly be ok, but at least know. Some knives you’d want to be able to sharpen with a file. Much depends on kind of steal and type of knife. If the file cuts deep and digs in, this indicates maybe 55 rockwell and this is usually getting into ‘did not take the heat treatment correctly.’ Keep an eye working the length of the blade and see if it is consistent. Do both sides as well. If not consistent, this could mean the blade was not evenly hot in the heat process or the steel has some inconstancies, internal stress. I want to control the edge and have the tip not as hard so tip less likely to break if dropped or stabbed into stuff.