Quote from: wootz on November 04, 2019, 03:56:26 AM

Grind a single-bevel blade and a double-bevel and observe difference between the resulting edge angle and the calculated.

Then grind 2 double-bevel blades of differing thickness behind the edge and observe difference between the resulting edge angle and the calculated.

Then take the thicker blade and grind it at 20 degrees, and at 12 degrees, and observe how the deviation from the calculated angle increases.

TormekCalc calculations are made

**in the axis of the jig and the knife**, so results are valid for

**all symmetrical double bevel knifes**with defined angle

**at the top of the edge**. Error given by material thickness is suppressed there completely.

For

**single bevel knives**is a correction necessary to get "right" axis of the jig. For this you can change diameter of USB or jig diameter value and "virtually" move the jig axis to the right place. Then you get

**exact results**for single bevel knifes with defined angle

**at the top of the edge**. Error given by material thickness is suppressed by the jig axis movement.

What is still present is

**error given by "roundness" of the wheel**– see picture Edges.jpg – which caused that

**angle increases along the hollow**. As you can see, the error is bigger with thicker material.

The essential thing is that

**you cannot eliminate* this error**when grinding on rounded wheel. The only thing you can do is

**. Then you get the desired angle at the edge heel**

**shift desired grinding angle closer to the edge heel****but angle at the top of the edge will be smaller accordingly**. If you shift the desired angle to the middle of grinded edge then you get smaller angle at the top of the edge and higher at the edge heel.

In view of the above, it is necessary to ask:

**Which point on the edge is the right one for the defined angle?**Top? Middle? Heel? Something between?

It's no problem to do it in TormekCalc – just change the jig projection length and you will get desired angle at the point where you want. Small corrections are sometimes needed while grinding because of change of the jig projection length, or measurement errors. It's really not dark magic or rocket science.

Quote from: wootz on November 04, 2019, 03:56:26 AM

What Ton does not mention, but I've found out, is that grinding with the wheel rotation goes differently to grinding into the wheel and requires additional mathematics. Therefore, you will see that the angle calculated for the Frontal Vertical Base by _TormekCalc.xlsx deviates from real edge angle even more.

Sorry, without detailed explanation this doesn't make a sense.

I don't have any problem with grinded angles while using my FVB (regardless of direction of rotation). It should be noted here that all constants in TormekCalc have been set for my T-8 and FVB and may differ in other devices.

Quote from: wootz on November 04, 2019, 03:56:26 AM

I understand that accepting that may be frustrating to you both, but we have to adjust maths to the real world, the vice versa doesn't work.

It's not about frustration, it's about precise inputs and corresponding outputs.

I made a robust testing on TormekCalc and I

**didn't find any problem with calculations**. Here I write about some limitations and

**explain why it is so**. TormekCalc is

**free**and everyone can test it and check its outputs. I have no evidence that there is something wrong except your claim, which is not specifically substantiated, so I try to make it right.

I have indicated that I have doubts about the accuracy of your measurements, which affect the grinded angle and the subsequent interpretation of the results.

There is why:

1. Jig projection length (video): Minimal supposed measuring/reading error

**±0,25 mm**

2. USB height (video): Minimal supposed measuring/reading error

**±0,1 mm**

3. Wheel diameter (video): Minimal supposed measuring/reading error

**±0,1 mm**

All these minimal errors together (in the worst scenario) will change the desired angle by ca

**±0,25° at the exact jig projection length**. Errors caused by FVB constants and by hand grinding aren't included.

4. CATRA Hobbigoni protractor (video)

Scale division is poor, supposed reading error can be ±0,5°, big reflection pattern can be other source of errors. Declared accuracy by Catra "measures the sharpened angles to an accuracy of ±2°".

Therefore I am skeptical of the reported results which seems to me inconsistent and

**I cannot simulate or verify them**.

*) Actually it's possible with flat grinding on diamond wheels or much more difficult way by changes of jig projection length while grinding.