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CollectorKnives Blog

Verifying Cutting Analytics

Remember the day when you sharpened your knife, shaved a few arm hairs, then put it work.  After a couple weeks you knew whether the knife was going to suit you or not.  Well, these days premium steels are coming at premium prices; and it is good to have those numbers independently verified in a scientific fashion instead of relying on an individual AHC (arm hair count).

There are a handful of independent professionals that can Rockwell test a knife and get a consistent and trusted reading.  But, once you have a steel and an HRC, then what?  What does that mean?

So, if you actually want to read analytics until your head hurts – proceed to the links below.  If not, let me simplify it – The website Knife Steel Nerds have done an outstanding job of using steel characteristics and hardness readings to predict a blades cutting life.

Below are listed some good articles on the subject:

Maximizing Edge Retention – What CATRA Reveals about the Optimum Edge

Sharpness vs Cutting Ability

Which Steel Has the Best Edge Retention? Part 1

Which Steel Has the Best Edge Retention? Part 2

Can CATRA predict Rope Cutting Performance?

Personally, I don’t cut a ton of rope.  But it seems to have become a benchmark that many are using.  So, I thought I would give their algorithm a couple of tests.  Who is CATRA?  CATRA (Cutlery and Allied Trades Research Assc) is a lab in England that has been analytically testing cutlery and producing testing equipment for nearly 70 years.  First a couple of definitions are from CATRA.  TCC is the CATRA test “Total Card Cut” and ICP is “Initial Cutting Performance”.  To understand the process and references you can review their respective page on the process.

Here is Knife Steel Nerds Algorithm.  It will predict the TCC given the HRC and edge angle – the rest are steel composition components.

TCC (mm) = -157 + 15.8*Hardness (Rc) – 17.8*EdgeAngle(°) + 5.0*Fe3C(%) + 11.2*CrC(%) + 14.6*CrVC(%) + 26.2*MC(%) + 9.5*M6C(%) + 20.9*MN(%) + 19.4*CrN(%)

So, I had a couple blades that have been tested by Peter’s Heat – thus I had a good idea of the HRC.

lionSteel Dom: With an M390 blade at HRC of 59.5 and an edge angle of 34 degrees inclusive (more on this number later); the algorithm predicted a TCC score of 574.

lionSteel Bolus Clip: With an M390 blade at HRC of 60.7 and and edge angle of 34 degrees inclusive (more on this number later); the algorithm predicted a TCC score of 593.

The reason I used 34 as the edge angle was that CATRA has a machine called the CATRASharp that will put this edge on a knife.  Since the actual edge put on the knife was the last “manipulatable” component variable – I decided to just standardize on their edge and their testing for a result that could be compared apples to apples going forward.  Not that anyone would sabotage the edge, just to get the result they wanted – but simply due to consistency from one person to another.

They also have Rockwell and Vickers testing equipment.  After discussing it with them, they felt the Vickers would do a more accurate job out on the actual body of the blade as there were concerns about movement when force was applied on their HRC equipment (they actually witnessed it with the microscope).  Vickers, according to CATRA, is a more complex test but more accurate in its readings.  So, since Vickers is easily converted the HRC; we went with their recommendation and standardized on Vickers results.

So, the blades went to England.  And when the results come back I was actually a bit surprised at how close the prediction was.

Dom: Prediction of 574TCC at 59.5HRC; came back at 646TCC.  ICP was 103 and actual hardness was 722HV/59.4HRC.

Clip Bolus: Prediction of 593TCC at 60.7HRC; came back at 648TCC.  ICP was 120 and actual hardness was 786HV/61.9HRC.

Although there are variances in this testing, just as there are many variations in the edge itself – I was very impressed with the predictor algorithm by Knife Steel Nerds.  We also plan to test a bit more with various angles, etc.  But for now I am very comfortable in predicting the performance on the back of the hard work put in by the “pros”.

As to correlations between the CATRA results and actually cutting rope; again, I will leave that to those that wish to do so.  There is simply too many other variables in this activity for me to feel comfortable.  But it is good to know that the “Nerd” has an analytical correlation already in place for that as well.