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Hardness and Ease of Deburring - KnifeGrinders - 08-18-2018

Many thanks to Mike B. for the A2 blades - they keep us entertained with testing this weekend.
A2 tool steel is high carbon, high molybdenum.
The A2 blade #7 has been hardened to HRC 54, while the A2 blade #11 to HRC 62 - they represent extremes of the knife hardness range.
[Image: A2_blades.JPG]
This simple study is to compare how the blades differing only by hardness respond to deburring.
These two blades have been sharpened exactly the same way, and edge sharpness scores recorded through the process.

The results have come with no surprises: the harder steel is easier to deburr and get sharper.

The blades were bevelled at 15 dps on Tormek using CBN wheels, the edge set on CBN #1000 edge-leading.
Off the #1000 CBN wheel a tiny burr was visible.

[Image: A2_grinding.JPG]

Deburring was done on a paper wheel with 5 micron diamonds at the exact edge angle, i.e. 15 dps, with the help of our support for controlled-angle honing and computer software.
Finished on a paper wheel with 0.5 micron diamonds to see effect of burnishing.

5 microns correspond to JIS #3000, and 0.5 micron to # 30,000

[Image: A2_deburring.JPG]

In the context of this study, higher BESS numbers indicate a larger burr.

SHARPENING STEP - HRC54 - HRC62 (BESS sharpness score)
Off #1000 CBN - 197 BESS - 159 BESS

Paper Wheel with 5 micron diamonds at 15 dps
2 passes alternating sides - 193 BESS - 138 BESS
4 passes alternating sides - 187 BESS - 127 BESS
6 passes alternating sides - 127 BESS - 72 BESS

Paper Wheel with 0.5 micron diamonds at 15 dps
1 pass alternating sides - 321 BESS - 114 BESS     << burnishing effect - in the softer steel more metal gets displaced over the edge apex, forming a wire edge.

Paper Wheel with 0.5 micron diamonds at 15.4 dps i.e. higher-angle honing at 0.4 degree higher
1 pass alternating sides - 109 BESS - 95 BESS
final sharpness

That's it, only will have to update this post with sharpness scores taken in 24 hours to see if there is difference in the post-sharpening spontaneous dulling.


RE: Hardness and Ease of Deburring - EOU - 08-18-2018

Good stuff KG. Not much doubt in our minds that the harder steels were easier to deburr than the softer steels and that all seems to correspond with final sharpness. You did a right fine job of sharpening these two pieces as well. Much better than us. We should be embarrassed but instead will attribute your high level of success to the fact that you have kangaroos and we don't.

We were surprised that that they tested as well as they did straight off the #1000 CBN before any deburring. Is this a quality of CBN or did we misunderstand the data? 

Looking forward to see how much (if any) they move after resting for awhile.


RE: Hardness and Ease of Deburring - KnifeGrinders - 08-18-2018

... in 17 hours after sharpening the sharpness scores are:

HRC54 = 152 BESS, worsening by 43;
HRC62 = 111 BESS, worsening by 16.

HRC62 is near 3 times better off.

This makes sense as you would expect that a softer steel gets stressed more during sharpening, and the post-sharpening changes in the edge apex would therefore be more pronounced in the softer steel. Definitely so when sharpening on CBN or diamonds using light pressure.
Might be opposite though if sharpened on softer abrasives and clogged stones or worn belts - I can imagine one would need to apply more pressure and time for the hard HRC62 steel and eventually it might get stressed more.

"We were surprised that that they tested as well as they did straight off the #1000 CBN before any deburring. Is this a quality of CBN or did we misunderstand the data? "
True, off CBN and diamonds the burr is times smaller than after a stone of the same grit - the scratches left by CBN/diamonds are narrow and deep, while by stones are shallow and wide displacing more metal.


RE: Hardness and Ease of Deburring - Bud - 08-18-2018

That was good and very interesting information Mr. Knife Grinders. Thank you for all your studies. A lot of work and a lot of good knowledge gained.


RE: Hardness and Ease of Deburring - KnifeGrinders - 08-18-2018

I asked Mike for the HRC54 and HRC62 samples because they represent extremes in the range the knives are commonly hardened, and by our experience require different approach to get them sharpened very sharp - I'll be sharpening and testing, sharpening and testing these two till get better understanding how to sharpen hard vs soft blades.
The above routine is not how we actually sharpen knives, but it is good to reveal the basic differences.

But first will SET-test them to get firm data on which holds the edge better in the long run, as Grepper noted in another thread we don't have these data yet. Will post the results later today or tomorrow.


RE: Hardness and Ease of Deburring - grepper - 08-18-2018

HRC54 = 152 BESS, worsening by 43
HRC62 = 111 BESS, worsening by 16


That is interesting Mr. KG.  A difference of 27.  I wonder if this holds true over multiple tests with different knives and steel types.  Not sure I'd notice the difference when slicing my breakfast kohlrabi the next day, but nonetheless a curiosity.

It's interesting to see folks on knife forums fussing about a couple of gram difference in sharpness along the edge of their knives, and now we can actually present carefully controlled studies like yours showing that just letting a blade sit overnight can result in a 43g reduction in sharpness.  I have little doubt this is not commonly known and will come as a surprise to many sharpeners.

Thanks for sharing!