EDGE RETENTION/ROLLING PART II

[EOU]

This represents a lot of work Subwoofer and your efforts are very much appreciated.

[grepper]

Yes, thanks for the work and for sharing the data. Very interesting.

I found it helpful for comparison to know that the average Series 1 Degradation = ~280.

I also notice the fairly large difference in Edge Angle Inclusive was between 20 and 50 (10° dps - 25° dps), which makes me question how useful the Series 1 Degradation average is for comparison.

That said, I don't know how much bevel angle effects SET rolling induced degradation, especially Series 1.

[subwoofer]

Sorry for being so thick-headed, but does series 1 mean you did one cycle (forward/back again) 5 times?

Yes. What was previously known as a 'set' (now not used due to the name of the SET machine itself), is now a 'series'. A 'series' being 5 'cycles' and a 'cycle' being one forwards and backwards motion of the impactor roller.

[grepper]

Thanks for the clarification Mr. Subwoofer. I like the term series/cycle over sets too. One set on the SET could be very confusing! I'd probably have to sit and puzzle out set and SET. Especially for an old brain like mine, that would be two too many sets of SET's to think about.

[KnifeGrinders]

Interesting to see that of all only the lower-ish end cheap 420HC steel holds a working edge after 2 series of rolling.

[grepper]

Mr. KG uttered, "Interesting to see that of all only the lower-ish end cheap 420HC steel holds a working edge after 2 series of rolling."

I wish all the knives had been sharpened to the same bevel angle as that would remove one variable that my effect degradation especially in Series 2.
 
The two Gerber Center Drives 420HC blades that showed the least Series 2 degradation were @ 20° dps., but one of the worst performers was the Gerber Sharkbelly 420HC @ 24° dps.  Almost the same bevel angle.
 
The hardest blades, Hultafors and Morakniv also had the most acute bevel angles @ 10 dps and 13 dps respectively almost half that of some of the others. 
 
Intuitively it would seem that a less acute bevel would perform better in Series 2 as the edge would thicken more quickly.
 
That said, the EOU tests indicate that for most intents and purposes there is not a significant enough performance variation between HRC 50 and HRC 62 to really worry about.  Did the EOU tests test for bevel angle?  At the moment I don’t recall. 

Mr. Subwoofer, I like the way you presented your data.

[KnifeGrinders]

@subwoofer
Your stropping recovery is very effective.
Could you describe your strop and the stropping method please?
Clean leather or with a honing compound; strokes at the edge angle or higher-angle; how many strokes each side on average?

[EOU]

Not to step into the middle of your question to Mr. Woofer here KG but yes, we agree. The two Hultifors knives are the exception though and we find that interesting. We don't have any suggestions for why this would be but just wanted to draw attention to those two exceptions. We will also take opportunity to say once again Subwoofer, this was a great piece of work and even more so when looked at in its totality. Now we'll butt out and let Subwoofer answer your question KG.

[KnifeGrinders]

Effect of Hardness on Edge Retention

Many thanks to Mike B. for sending us samples of A2 tool steel.
A2 is a high carbon, high molybdenum tool steel.
The A2 blade #7 has been hardened to HRC 54, while the A2 blade #11 to HRC 62 - they represent extremes of the common knife hardness range.


We sharpened these two blades exactly the same way at 15 degrees per side (dps) on Tormek using CBN wheels, the edge set on CBN #1000 edge-leading. Deburring was done on a paper wheel with 5 micron diamonds with the help of our support for controlled-angle honing and computer software.

The initial sharpness was very close, 109 and 114 BESS.
The 2 blades have been subjected to controlled edge rolling on the BESS SET tester.

Rolling cycle explained
The impact roller is a linear bearing slant at 10° to the horizontal base or in other words at 80° to the plane of the blade clamped vertically.
Standard impact assembly weight is 150 grams.
The impact roller is lowered at "A", then moved (rolled) over to "B" and then back to "A".
A-B-A is one cycle.


The results have shown a tremendous difference in edge holding.

It took 45 rolling cycles to blunt the HRC-54 blade to 500+ BESS.

The HRC-62 blade holds a working sharp edge at least 10 times longer.
I say "at least" because even after 500 rolling cycles the HRC-62 kept scoring a working edge of under 500 BESS. By then I had been rolling the HRC62 for 1 hour, and just gave up on blunting it. For comparison, mainstream knives blunt to 500+ BESS within the first 100 rolling cycles.

Link to raw data >>

Chart


However, despite that extraordinary edge holding, the HRC-62 blade won't hold the super-sharp edge any better.
The initial blunting rate is relatively rapid regardless of hardness.
Initially both the HRC54 and HRC62 blades were scary sharp near 100 BESS, but it took only 1 rolling cycle to blunt them to just sharp, and 5 rolling cycles to working edge.
The divergence of sharpness graphs in the chart starts at about 350-400 BESS - the HRC-62 sharpness stays at this level through continued rolling impacts, while the HRC-54 sharpness deteriorates almost linearly till blunted to practically unusable.
400 BESS is what real world working edges score, and the A2 @ HRC62 holds this edge extremely well - we've seen that good edge retention only in Vanadis-10 and ceramic knives.


Key Indicators

[Jan]

Mr. KG, thanks for sharing your new results!  

Increase in blade hardness corresponding the transition from HRC 54 to HRC 62 is large, some 38%, but the increase in edge holding is really tremendous!

Jan