Sharpening for a better burr

[Ken S]

Jan,

Alas, I believe our feeble English language has become the standard language for the world. Your English is fine, and your thoughts are interesting.

Ken

[Jan]

Doug and Ken, thanks for your appreciation. 

Jan

[Ken S]

Jan,

The three knife jig position drawings you post give me a question. Is the jig placed equidistantly between the tip of the knife and where the blade joins with the handle of the knife. If not equidistant, perhaps there is a proportion which could be measured and replicated. If so, that would make obtaining a consistent bevel less hit and miss. Thoughts?

Ken

[Jan]

Ken, you are asking a very good question. 

The knife jig is generally not placed equidistantly between the tip of the knife and where the blade joins with the handle of the knife, despite the fact that it can sometimes happen.

For grinding the same edge angle at the tip and at the straight part of the blade we have to mount the knife so, that the distance between the place where the tip of the pivoted knife touches the stone and the rounded margin of the jig's stop is the same as the distance between the place where the straight part of the blade touches the stone and the jig's stop.
The length of the red line should be the same as the length of the blue line in the figure below.

The requirement for equality of lengths of the red and the blue lines may often not be met exactly. Usually I start with mounting position based on distances measured between the thumb and index finger.

Jan

[Herman Trivilino]

If not equidistant, perhaps there is a proportion which could be measured and replicated. If so, that would make obtaining a consistent bevel less hit and miss. Thoughts?

It depends on the angle at the tip. If you have butcher knife with lots of curvature at the tip it's different from a pocket knife blade that has very little curvature at the tip.

Jan's equidistant red and blue lines is a scheme consistent with what Jeff taught us.

I agree with the notion, and am happy to have learned from this discussion, that a combination of lifting and pivoting is required.

[Jan]

Fully agreed, Herman!

Thanks for your confirmation that my thoughts, concerning knife pivoting, are in compliance with Jeff's lessons. 

Jan

[Ken S]

Jan, I think this is a good idea which could benefit from further refinement. Using your photo, I want to try drawing a marker line in the center of the wheel where the flat part of the knife edge meets the grinding wheel. Then, without turning the Tormek on, go through the lift and pivot motion and see if the tip ends up on the center mark. This would show both if the tip was hitting the same line and also the same center spot on the wheel.I believe this would efficiently increase the consistency of the bevel angle.  Thoughts?

Ken

[Jan]

Yes Ken, I fully agree with your intention. 

I would like to draw your attention to one tiny thing. Strictly speaking, the procedure under discussion should ensure the same bevel angle only for the straight part of the blade and the point of the blade tip. It is significant improvement, which is worth of further refinements.

Nevertheless, there is no guarantee concerning the consistency of the bevel angle along the the curved part of the blade (e.g. blade belly). Fortunately for common blade shapes this difference is not significant.

Jan

[Ken S]

Jan,

I will accept any improvement that I can get in precision and efficiency....and hope for more. I do believe this is worth exploring. Consistency in bevel angle is one of the strong pointsof the Tormek; let's maximize it.

Ken

[Elden]

   If the same line (point) of contact with the grinding wheel is maintained, I would think any edge angle variation would be a miniscule amount. If you are into free handed grinding, how perfect of a angle do you consistently achieve?

   By the way Jan, I imagine your English is better than mine.

[Jan]

Yes Elden, you are correct! 

When I find some time I will try to estimate the size of the edge angle variation caused by the fact that some part of the blade bally occurs above the same line of contact with the grindstone.

What concerns my English, I am preparing my posts offline in MS Word and use spellcheck to avoid spelling mistakes. 

Jan

[Jan]

Jan,

I will accept any improvement that I can get in precision and efficiency....and hope for more. I do believe this is worth exploring. Consistency in bevel angle is one of the strong pointsof the Tormek; let's maximize it.

Ken

Ken, I think it will be an easy task for you to design a modified knife setting jig.

Your modified jig may be wider and will probably display circular arc with the centre at the rounded corner of the Tormek knife jig stop. The arc radius will be equal to your magic length of 139 mm.

Using fig.5 from your knife setting jig documentation, your modified jig will have to ensure that the lengths of the red and the blue lines are equal.

Jan

[Elden]

   For purpose of clarity, I am going to use the term "line of contact" to refer to the line where the straight portion of the knife edge contacts the grinding wheel. Steve  referred to it as a point. I am going to abbreviate "line of contact" to "LOC".
   As it has been said, the "LOC" can be physically scribed on the grinding wheel when it is at rest. When the grinder is switched on, the scribed "LOC" becomes only a line (location) retained in your memory. The straight portion of the knife edge shows us where the"LOC" is located while the grinding wheel is in motion. Jan has shown how to mount the knife so that the the knife point meets the "LOC".
   While grinding the belly of the knife, we have to rely upon our memory retention of where the "LOC" is located. This is while using the standard Tormek knife jigs. Free hand grinding would cause one to retain the "LOC" in memory the entire time. Steve has shown a good way to obtain it initially (see his book Sharpening Made Easy or his informative web site, sharpeningmadeeasy.com).
   If we strive to keep the knife edge at  the "LOC" while grinding the edge (the belly included), it would appear to me, a consistent bevel angle can be achieved.

[Ken S]

Use of a laser pointer to locate the LOC (or Point of Contact) seems overkill to me, however, there may be some simple solutions. I think it is worth exploring.

Ken

[Jan]

   For purpose of clarity, I am going to use the term "line of contact" to refer to the line where the straight portion of the knife edge contacts the grinding wheel. Steve  referred to it as a point. I am going to abbreviate "line of contact" to "LOC".
   As it has been said, the "LOC" can be physically scribed on the grinding wheel when it is at rest. When the grinder is switched on, the scribed "LOC" becomes only a line (location) retained in your memory. The straight portion of the knife edge shows us where the"LOC" is located while the grinding wheel is in motion. Jan has shown how to mount the knife so that the tip meets the "LOC".
   While grinding the belly of the knife, we have to rely upon our memory retention of where the "LOC" is located. This is while using the standard Tormek knife jigs. Free hand grinding would cause one to retain the "LOC" in memory the entire time. Steve has shown a good way to obtain it initially (see his book Sharpening Made Easy or his informative web site, sharpeningmadeeasy.com).
   If we strive to keep the knife edge at  the "LOC" while grinding the edge (the belly included), it would appear to me, a consistent bevel angle can be achieved.

I agree with you? Elden! 

I have only a minor comment concerning bevel angle consistency.

To keep the edge angle the same along the entire blade is possible only in free hand grinding regime.

When we use Tormek knife jig, with the knife mounted so that the tip meets the LOC, than the belly of the pivoted knife edge usually goes beyond the LOC. This means that the belly has slightly smaller edge angle.

Jan