Honing Wheel LA-220 edge-rounding root cause

[wootz]

Not sure if this is news to the Tormek community, but actual honing wheel LA-220 diameter is 215 mm.
If you set your honing angle at the 220 mark that is in bold on the AngleMaster, you will inevitably round the edge.
Correct is setting it at 215 mark - as shown by the red line on the photo:

[Dutchman]

Thanks Vadim.
I should have added a table for 215mm, but I supposed that the 220mm was correct. 

[wootz]

  I kept wondering why BESS score worsens after honing my knives, till I questioned the leather wheel diameter.
Had to redo my applet for the frontal vertical base honing angle because of that.
BTW I have it now for Mac as well.
Not that i think you need help with calculations , yet let me know if you want it.

[Jan]

Wootz, your observation is correct! Diameter of my honing wheel is 215 mm also.

Based on my calculations, ignoring this fact will cause that we are honing a bevel angle changed by some 1.3°.  (I have assumed projection length of 139 mm and 15° bevel angle.). 

Jan

[wootz]

Thank you, Jan, I've been waiting for your estimate, I knew it's coming.
My tests show that the edge can survive burial into the honing wheel up to 0.5 degrees, but from +0.6 degrees it loses sharpness dramatically.

[Ken S]

Not being a mathematician, I note that Dutchman's tables for a 15° bevel and 85mm Distance (between the universal support and the grinding wheel) shows a Projection of 141mm with a 220mm diameter grinding wheel and a 135mm Projection at an 80mm Distance. Since I standardized on 139mm Projection with the kenjig, I would make a kenjig with a Distance setting groove of 83.5mm, actually a thin reading (like 83.4). The same Distances with the 210mm diameter chart show 139 and 134mm Projections. I would just split the difference, and make a kenjig for 215 mm diameter at approximately 84.2mm. I am quite sure even this approximation is beyond the accuracy of any measurement tool graduated in one degree increments.

Unlike a kenjig made for a gradually consumable conventional grinding wheel, the Distance should not vary over time with a leather honing wheel.

What puzzles me with this is that the smaller Distance reading for 220mm diameter would tend not to polish the very edge of the blade. Using a larger Projection number (from a smaller diameter table) would tend to add a slight micro bevel (secondary bevel). Although I have not tested it, it would seem logical that the reading from the 220mm chart would have no effect on the BESS readings, as the Distance would in effect be designed for a slightly smaller bevel angle and the edge barely touched.

I can't believe that the Tormek engineers would mismeasure the diameter by 5mm. There must be a logical reason for the difference. It would be interesting to know.

Ken

[Jan]

Not being a mathematician, I note that Dutchman's tables for a 15° bevel and 85mm Distance (between the universal support and the grinding wheel) shows a Projection of 141mm with a 220mm diameter grinding wheel and a 135mm Projection at an 80mm Distance. Since I standardized on 139mm Projection with the kenjig, I would make a kenjig with a Distance setting groove of 83.5mm, actually a thin reading (like 83.4). The same Distances with the 210mm diameter chart show 139 and 134mm Projections. I would just split the difference, and make a kenjig for 215 mm diameter at approximately 84.2mm. I am quite sure even this approximation is beyond the accuracy of any measurement tool graduated in one degree increments.

Ken, you are correct, you have used a linear interpolation method which is believed that it was used by Babylonian astronomers. Currently it is used in all modern computer graphics processors. 

The exact Distance is 83.9 mm using the Dutchman's approach for 215 mm wheel diameter, 15° bevel angle and 139 mm projection length.

Jan

[Jan]

Thank you, Jan, I've been waiting for your estimate, I knew it's coming.
My tests show that the edge can survive burial into the honing wheel up to 0.5 degrees, but from +0.6 degrees it loses sharpness dramatically.

Wootz, you are welcome! 

Your observations concerning abrupt loss of edge sharpness are very interesting for me. Have you observed the same behaviour also when honing "chisel grind" blades buried into the honing wheel? 

Jan

[wootz]

Thank you, Jan, I've been waiting for your estimate, I knew it's coming.
My tests show that the edge can survive burial into the honing wheel up to 0.5 degrees, but from +0.6 degrees it loses sharpness dramatically.

Wootz, you are welcome! 

Your observations concerning abrupt loss of edge sharpness are very interesting for me. Have you observed the same behaviour also when honing "chisel grind" blades buried into the honing wheel? 

Jan

This was a full-range study (unrelated to the LA-220), will be published in the US Sharpeners' Report in their December issue. I will send you a complimentary copy then.
For now can only show you the chart of BESS score as function of the Honing Angle - treat as a spoiler 

[Stickan]

Hi all,
Very interesting topic.
Sharpening a chisel at 25-30 degrees the difference between setting the diameter on 215 mm or 220 mm is 0.46° when using the WM-200 angle-master.
Noticeable is that the angle will be less on 215 mm than 220 mm.

There are some things needed to be considered measuring this. Using stones to hone with will result in a different result than with a leather honing wheel.
The leather is so much softer than a stone that it will not round the edge. To round an edge you need to have much more angle difference than 1 degree.

The idea used by us and most manufacturers is that a increased polish on the tip will make the edge finer.
For knives this is common. You can have a original grind at 28 degree and a polished edge at 2-3 degrees. Almost like a secondary edge but hardly noticeable.
A chisel will not get a less sharp edge if the back is 100% plane. A rounded edge on a chisel is mostly because the back is not flattened correctly.

The LA-220 setting on the Angle master is necessary to get the burr of the edge. If we would have a setting of 215 mm the burr would be hard to hone away. The leather is very soft and the measurements could maybe be transferred to a stone but not on a leather honing wheel.

Honing is an issue where I think that practise makes all the difference. Using the jig to hone a chisels edge but free-hone the back can be tricky. It's easy to round the back and that's the issue in most cases. Setting the anglemaster at 220 as our design is,  will not be the reason for a rounded tip.

Sincerely,
Stig

[Jan]

This was a full-range study (unrelated to the LA-220), will be published in the US Sharpeners' Report in their December issue. I will send you a complimentary copy then.
For now can only show you the chart of BESS score as function of the Honing Angle - treat as a spoiler 

Wootz, thank you very much for your additional info from your paper in print. I am really eager to read the whole study, especially your discussion of the interesting results. 

Jan

[Dutchman]

This was a full-range study (unrelated to the LA-220), will be published in the US Sharpeners' Report in their December issue. I will send you a complimentary copy then.
For now can only show you the chart of BESS score as function of the Honing Angle - treat as a spoiler 

WOW! That is very convincing! Thanks. Are you going to post that publication here too? I would love to have a copy of it.

[Jan]

Stig, thank you for your statement to this interesting topic. Much appreciated! 

Based on my calculations for a knife blade mounted in a knife jig at 15 degrees bevel angle and 139 mm projection length the difference between setting the diameter on 215 mm or 220 mm is 1.3 degrees. 

Based on my calculations for a chisel at 25 degrees mounted with protrusion 50 mm in the SE-76 jig the difference between setting the diameter on 215 mm or 220 mm is 0.42° which is in compliance with your figure. Sorry, I made an error when I was simulating the angle setting by the 220/215 mm procedure using my older Excel scripts.

Regards
Jan

[Stickan]

Jan,

"Based on my calculations for a chisel at 25 degrees mounted with protrusion 50 mm in the SE-76 jig the difference between setting the diameter on 215 mm or 220 mm is 0.42° which is in compliance with your figure."

We checked some different protrusions and the result was between 0.01-0.05° which is not noticeable.

I would say we are down to really nerdy info now :-)

Of coarse there is a difference with a knife and a chisel.
It would be very interesting to know how the knifes are honed. Is the result the same when using the knife jig or honing freehand?

Best,
Stig

[Jan]

Stig, you are correct again!  The difference between setting the diameter on 215 mm or 220 mm when using the WM-200 angle-master shows only weak dependence on chisel protrusion.

Regards
Jan