Best microbevel angle

[wootz]

Best microbevel angle

Test procedure we used was to set a secondary bevel using a Japanese grit JIS #800 wheel (grain size ~ 15 microns), edge-leading;
then set a microbevel at a larger angle with an SJ Japanese grit JIS #4000 wheel (grain size ~ 3 microns), edge-trailing;
the edge was then deburred*, and sharpness tested with a BESS edge sharpness tester.

We tested microbevels at 0.2 degree interval from +0.2 degree to +1 degree (per side).
In other words, tested edge sharpness where the grit #4000 grinding angle was 0.2, 0.4, 0.6, 0.8 and 1 degree larger than the angle at which the grit #800 bevel was set.
We then repeated the test for the best scoring microbevel to rule out random factors, and tested that range at 0.1 degree interval.

The best edge sharpness gave microbevel of 0.5 degree larger, i.e. 1 degree inclusive.
It scored 50 BESS, which approximates to 0.5 micron edge apex width.

We needed these data ourselves for one of our sharpening methods, but given their practical importance, share here with the knife community.

Full test results follow.
Grit #800 set bevel was 15 degrees per side, i.e. 30 degrees inclusive.

Grit #4000 microbevel angle per side - BESS score on PT50B edge sharpness tester
15.2 - 200 BESS
15.4 - 70 BESS
15.5 - 50 BESS
15.6 - 65 BESS
15.7 - 90 BESS
15.8 - 100 BESS
16 - 105 BESS

-------------------------
Grinder - Tormek T8 (#800), and T7 (#4000).
Knife - SWIBO at 58 HRC from our rental pool.
Edge sharpness tester - PT50B Professional.
*Deburring was done by a single pass each side on a paperwheel with 0.25 micron diamond paste, set at the angle of the microbevel.

[Dutchman]

Is the recommended angular difference between primary and secondary bevel dependent on the angle of the primary bevel?
In his publication Experiments on Knife Sharpening (http://www.bushcraftuk.com/downloads/pdf/knifeshexps.pdf)  John Verhoeven recommends a 2β target hone angle set to around 5° to 6° larger than the ground angle of 40° (page 26-27)
So he applied a secondary grinding angle 2.5° larger, at a primary grinding angle of 20°.
It is a large difference with 'your' 0.5°, a factor 5!
Difference in the accuracy of setting or measuring the grinding angle might be the reason? 

[Ken S]

Very interesting topic! Wootz, kudos for the research, and, Dutchman, very astute observations.

This is an excellent use of BESS. BESS gives us a quantifiable, repeatable platform for testing.

How did you set the bevel angles? .1° increments are beyond the limits of the Anglemaster, just as .001" differences are beyond the limits of even the finest rules like those made by Starrett. What comes to mind is an extension of Dutchman's tables with a kenjig and feeler gages.

Edges with this level of sharpening seem more in the realm of very high end work than day to day. (Nice work if you can get it, and have the skill to do it!)

Good work, Wootz!

Ken

[wootz]

Thank you, Ken.

I set grinding and paperwheel angle with the help of computer software, and verify with a CATRA laser protractor.
Our computer scripts set exact grinding angle; but given the manual setup, real life accuracy is 0.1 degree.
The microbevel is seen as an additional bright dot on the protractor scale outside the laser reflection from the main secondary bevel; this dot is so bright and clear compared to the reflection from the rougher secondary bevel, that allows precise reading from the protractor scale.

The computer scripts are based on Ton Nillesen's trigonometry for Tormek grinder, and are described in this section of our website:
http://knifegrinders.com.au/05Equipment_scripts.htm

[wootz]

@ Dutchman

Secondary bevel done on grit #800 without microbevelling, and deburred on the same paperwheel scores 80-100 BESS (average of 6 test sharpenings).

As the above tests show, when microbevel is too shallow (+ 0.2 degree) you just round the edge.
The shallow microbevel of + 0.2 degree worsens the edge sharpness to 200 BESS.
In microns it means shift from a submicron edge apex width to 2 micron.

Some worsening also is seen at the microbevel +1 degree.
I didn't test larger angles, as this was beyond my sharpening problem these tests were to solve.
With all my respect to Mr. Verhoeven, with a too steep microbevel you'll be gouging the edge into the abrasive dulling it.

[cbwx34]

wootz,

Interesting test... for sure.

Have you tested setting your microbevel also edge-leading?  Some testing with another sharpener (tested similar to the BESS), showed an edge leading finish produced a better edge.  Be interesting to see if your testing supports that or not.

Also, what would a test finished on the 4K wheel without microbeveling show, (if you did that)?

Thanks for sharing.

[wootz]

wootz,

Interesting test... for sure.

Have you tested setting your microbevel also edge-leading?  Some testing with another sharpener (tested similar to the BESS), showed an edge leading finish produced a better edge.  Be interesting to see if your testing supports that or not.

Also, what would a test finished on the 4K wheel without microbeveling show, (if you did that)?

Thanks for sharing.

At https://scienceofsharp.wordpress.com/ is shown that edge-leading sharpening on fine grits from #4000 and finer damages the edge and worsens sharpness.
I won't be quoting from there, you better see yourself, it is an eye-opening study.

Sure I tested what the scienceofsharp says, and this answers your second question: the best edge-leading BESS score on SJ #4000 I could get was 120 BESS, with average 150-160 BESS, which is smooth forearm shaving against the skin in traditional sharpness tests.

Edge-trailing sharpening (or rather honing) on SJ forms a visible foil burr along the edge, that must be further removed by stropping, I do it on paper wheel. Without microbevelling, the resultant edge sharpness averages 65-85 BESS.

But if you test the foil edge before stropping, it gives an awful BESS score near 300 due to the bent foil. That might what that sharpener you quoted have seen...

[cbwx34]

...120 BESS, with average 150-160 BESS, which is smooth forearm shaving against the skin in traditional sharpness tests.

Since you mentioned this... is there a chart or comparison of what the different BESS numbers compare to (especially in the 'real world', like your example)?  I've seen the BESS website/forum... but haven't run across a comparison of what the numbers equate to.

p.s.  I've seen the "0-2000" chart... but it doesn't define the "level of sharp" I'm asking.

[wootz]

Yes, I have BESS scores for all traditional sharpness tests.

But this chart is due to be published in the Australian Knife Magazine in November, I am not allowed to make it public before that.
After November will share it on www.bessex.com

[cbwx34]

Yes, I have BESS scores for all traditional sharpness tests.

But this chart is due to be published in the Australian Knife Magazine in November, I am not allowed to make it public before that.
After November will share it on www.bessex.com

Haha... ok... thanks.  (Glad to see there's at least an interest in what the actual numbers mean....). 

[Jan]

Wootz, thanks for sharing with us the very interesting results of your ambitious experiment! 

The absolute accuracy of the portable Catra model is +/- 1.0° and for the bench model +/-0.5°. Relative accuracy is of course much better, but to estimate a 0.1° angular distance is still challenging.

In my thinking the laser dots on the circular scale of the portable goniometer for 15° bevel and 15.1° microbevel are less than some 0.2 mm apart.

Jan

[Jan]

Since you mentioned this... is there a chart or comparison of what the different BESS numbers compare to (especially in the 'real world', like your example)?  I've seen the BESS website/forum... but haven't run across a comparison of what the numbers equate to.

p.s.  I've seen the "0-2000" chart... but it doesn't define the "level of sharp" I'm asking.

It may be interesting for you to read how my granddaughter understands BESS. 
http://bessex.com/forum/showthread.php?tid=18

Jan

[cbwx34]

It may be interesting for you to read how my granddaughter understands BESS. 
http://bessex.com/forum/showthread.php?tid=18

Jan

Best "results" I've seen!!!      

[wootz]

Wootz, thanks for sharing with us the very interesting results of your ambitious experiment! 

The absolute accuracy of the portable Catra model is +/- 1.0° and for the bench model +/-0.5°. Relative accuracy is of course much better, but to estimate a 0.1° angular distance is still challenging.

In my thinking the laser dots on the circular scale of the portable goniometer for 15° bevel and 15.1° microbevel are less than some 0.2 mm apart.

Jan

That's it, Jan.
The bright dot reflected by the microbevel becomes distinctly visible on the laser protractor from 0.5 degree difference with the main secondary bevel, not earlier.
I wasn't saying I verified 0.1 degree intervals with the CATRA laser protractor, we rely on the computer scripts to set grinding angle with 0.1 degree accuracy.
The laser protractor was to confirm the microbevel is there, and the target edge accuracy.

Microbevel extra dot on the laser protractor: the main bevel reflection is at 15 degrees, and the microbevel next to it:

[Jan]

OK, Wootz, an angular difference of 0.5° corresponds to almost 1 mm distance between laser beam reflections which is by careful reading well visible.

Jan