Grinding software upgrade is coming

[wootz]

NEED FOR UPGRADE
In its current form, our software sets an accurate grinding angle for resharpening a knife with established bevels at the existing edge angle.
E.g. you resharpen a 15 degrees per side (dps) knife to the same 15 dps.

However, when grinding new bevels, sharpening a grossly dull knife or a knife blank gives an edge angle differing from the calculated target by 0.5-1.5 degree. The thicker is the blade behind the edge, and the lower is the new edge angle, the greater is the difference.

To complicate it further, when sharpening on a coarse wheel, you may get a higher than the calculated angle simply because the jig projection shortens as you grind off the apex and raise the burr.

For example, when you resharpen a thin kitchen knife on a fine wheel to the same edge angle as this knife already has, you get the edge angle within 0.1 degree of the angle calculated by our software. But when you sharpen a thick hunting knife on a coarse wheel, you get an edge angle by 0.5 degree higher if sharpened at the original edge angle, and by up to 1.5 degree higher if reprofiled to a lower angle.

If you have a laser protractor, observing how the edge angle changes in the process of shaping bevels gives a better understanding of what I am writing here.

NEW INTERFACE
The new interface has additional parameters in its "Blade" section, to address the above and improve accuracy.



STATUS
I've coded the computer algorithm and currently testing in sharpening blades of varying thickness.
The calculations are along the lines of the explanation given by Ton Nillesen in 2018 on the page 6 of his additional booklet that can be downloaded from our website http://knifegrinders.com.au/Manuals/Grinding_Angle_Adjustment_Booklet_2018.pdf

The blade position on the grinding wheel changes as the sharpening progresses, gradually lowering as the edge apex travels the distance of the blade thickness behind the edge, as shown on the following schema:


This downwards shift of the blade and the knife jig it is clamped in increases in the duller edge, the thicker blade, the coarser grinding wheel, and the lower grinding angle. If not corrected, the actual grinding angle will be differing from the target.

As I am happy with my testing, we will prepare an upgrade, first of the computer-based applications, Windows PC and MacBook, and email an upgraded download to our over 1000 customers.

I am not as sure about the mobile applets, though. iPad and tablets are no problem and we will sure upgrade them and find a way to deliver to our existing customers, but the phone screen may be too small to accommodate the additional settings.

We will also upgrade our Frontal Vertical Base software with these advanced settings. But again, the phone applets are a problem, as they hardly take even the current FVB interface.

As we all understand, this is not only about the edge angle accuracy, but for better matching the grinding and honing angle to get a sharper edge.

We will also have to update the applet manuals and our webpage with the new information.
Overall, we need about 1 month to complete this upgrade, and appreciate your patience.

Cheers, Vadim

[van]

Good job! we are waiting. You are great!

[Sharpco]

Great!

[smurfs]

Hi Vadim,

I observed similar behaviour when I was grinding the life out of my practice chisel. This was especially noticeable when I changed from a more to less acute edge angle as more of the edge was ground away to arrive at a flat bevel. I found that in the process of grinding the jig projection length was reduced by up to 1 to 2mm, throwing out the desired bevel angle by a similar number of degrees.

In my research I too measured the thickness of the bevel at the heel and modified my projection calculation so that the correct angle was achieved at the moment of burr creation. As a sharpening novice it is pleasing to read someone else with vastly more experience has arrived at the same point with an almost identical solution.

Cheers, Andrew

[John_B]

This will be a welcome addition. I have had several requests to change the angle on older European knives.

[Josu V]

In first place, thank yoy for your work.

I will be alert for possible update for IOS app.
Please...  if necessary, I will buy a high magnification glasses in order to can see the app in my smart phone. 
I always use my smart phone to calculate grinding and honing measures and find very interesting an update of the smart phone app.

Regards

[wootz]

In first place, thank yoy for your work.

I will be alert for possible update for IOS app.
Please...  if necessary, I will buy a high magnification glasses in order to can see the app in my smart phone. 
I always use my smart phone to calculate grinding and honing measures and find very interesting an update of the smart phone app.

Regards

Not to worry, Josu. We are blessed to have the best mobile apps programmer, he should be able to solve it with an extra screen for the additional settings. I haven't thought much about it yet as we are in the early stages of the upgrade. I only wanted to say that as I myself program for Windows, the computer-based applet will be ready first; others will follow.

[wootz]

We've completed testing of our updated software, the testing process and results are shown here:
http://knifegrinders.com.au/software_testing.htm

It has been an exhaustive testing. I didn't count, but overall we did near 100 test sharpenings. With the amount of experimental grinding and honing we've done using the Grinding Angle Setter and the Frontal Vertical Base applets, I am confident in the accuracy of our software. Those of your who have a laser protractor will be able to confirm it yourself as we release the update.

It is clear now, that thickness behind the edge is an important parameter that should not be ignored.

The mathematical description of the grinding angle given for Tormek machine by Ton Nillesen in 2013 is using an abstract blade, thin and single-bevel. This is a normal phase in scientific thinking, as we have to abstract from real-world particulars to be able to generalize and describe the reality mathematically. That model did not take into account the thickness behind the edge. Because of that, the formulas give a systematic error for thicker blades, especially double-bevel, as Ton Nillesen explains in his additional booklet in 2018.

Our updated computer algorithm factors in the thickness behind the edge, and specifics of double-bevel edge vs single-bevel. It is more complex, but also more accurate.

This, however, does not make our applets more complex to use.
For our customers who care about the edge angle accuracy, our software gives an accurate tool.
But those of you who prefer simplicity and do not care much about 0.5 degree deviation from the target angle, can simply put number "1" in the "Blade thickness" field for thin knives, and number "2" or "3" for thick knives. I will explain this in the updated manual.

The software is now with our MacBook and mobile apps programmers, and should be released within 2 weeks from today. I will then send the update for Windows, Mac, iPhone/iPad and Android smartphone/tablets to our existing customers free of charge.

[Dutchman]

Thank you for mentioning the source

[Jan]

I have shaped several blanks into blades without observing differences between the desired and sharpened bevel angle provided that the projection length has not been shortened during blank sharpening.

I use my Excel script to calculate the distance between the USB and the wheel surface. My script works without approximations.

Jan

[wootz]

Jan, sharpen plate steel 1mm, 2mm and 3mm thick to the same target angle using your script, and you will see difference in the ground angle between all the three.
.

[Jan]

Wootz, my experience is limited to 2.5 mm thick blanks which I shape to double-bevel blades. Blanks of this thickness are centred in the knife jig.

If the blank is not centred in the knife jig than the sharpened bevel angle will be different from the target bevel angle and even more the bevel angles will be different for each side of the blade.

Jan

[wootz]

Jan, are you implying we do not center blades in knife jigs before grinding? - we always do.
BTW, the Tormek knife jig SVM-45 centers a 2.1 mm blade, not 2.5 mm as you think.
Anyway, the blade thickness behind the edge matters for accurate calculation, even if using a self-centering jig.

Our software update is not only for the sake of the edge angle accuracy, but for better matching the grinding and honing angles to get a sharper edge.
As you guys can see at the http://knifegrinders.com.au/software_testing.htm the BESS Sharpness Tester PT50 showed 60-80 BES for the 12° and 16° edge honed with the Tormek honing paste at the ground angle. This is an improvement over what we observed in the past for the knife steels used in this testing.

[Jan]

Wootz, thank you for ensuring me that blade centring in the knife jig is not an issue.

I am asking for clarification because I am missing some geometrical sketch or drawing which would explain the merit of the sw upgrade. Your reference to page 6 of the Ton Nillsen (2018) booklet is not fully sufficient and explanatory.

It is my great pleasure to inform you, that I have carefully reviewed the revised Ton booklet (2018) and have found, that the formula F9 used to calculate the New tables is exact, derived without any approximations.  The figures in his New tables are now identical with my calculations. For some users it might be useful to display the figures in the New tables with one or two decimal points.

The exact formula F9 replaces the original formula F1 which was an approximate one and might cause a bevel angle set-up error up to 0.7 degree per one side. The use of the approximate formula F1 could also cause some inconsistencies between grinding and honing angles.

Jan

[smurfs]

Hi Vadim,

Could the angle issue simply be due to the reduction in the jig projection length during grinding, as illustrated in the schema diagram in your initial post? If it is would it not be better to recheck the projection after each grinding step in your sharpening procedure, and if necessary return to the initial projection length using the adjustable stop? Perhaps such a tweak is all that is needed to ensure the target edge angle is always maintained.

Or may be I've missed something and it is not as straightforward as I think 

Andrew