Lengthwise convex hone

[LJS]

however the whole point of these exercises are not to get to the lowest common denominator, are they? We’d have stopped buying/using new or other hones and razors (and other kit) once we hit that min ROI break point.

I agree completely that for most of us who enjoy honing, it is not just about making a razor sharp (lowest denominator).

But when you try new things and learn they do absolutely nothing at all….well then you learned (hopefully) that it was sort of pointless

Some changes in technique, equipment, etc equate to a different results. Some do nothing at all or virtually meaningless.

To be contributing here and not just shooting holes in you guys’ theory and experimenting, I will say I generally flatten stones….but once upon a time I used to believe that it was super critical and the tiniest fault in flatness would result in sub-par edges. It’s not totally true. It’s just not. I can pick up a convex or concave or even a stone that has both convex and concave areas…..and I can generally hone a great edge. I have numerous oddly shaped stones that are hundreds of years old and seen massive amount of work and abuse…..and still great edges. So that theory or even mantra was not totally fact.

There is so much emphasis on the equipment but really the skill is more important. It really is. A great honer can use poor stones but great stones can’t help a poor honer. I would rather have a razor sharpened on a dished 1000 grit stone from a seasoned honer than what some folks produce from a pile of choice stones. This is what really moves the needle. So, when you get into the theory of honing on theoretical 30’ diameter balls……I first wonder if the person has the skills to actually produce a difference in edge…..and if yes the second…..is such a ridiculously minute different really noticeable anyway (NO). I was into target shooting most of my life and it used to crack my up to watch people dump money on parts and equipment that were 1000x more refined than their shooting ability - if they can’t shoot a rifle out of a box straight then how is a new fancy trigger and scope going to help? Same with honing - you first have to have the ability to hone well enough to notice that difference.

Couple of years back I experimented with honing on the large-radius sides of a set Arkansas slip stones. I wanted to see first hand an extreme version of all this contact point discussion and convex theory everyone was arguing about. I point out theory because you have to prove or disprove to be fact. I thought this curvature would be an extreme for sure. Reductio ad absurdism. Interestingly it honed just fine. For me anyway. I could see though as I did it how it could be screwed up easily if someone didn’t have smooth motion in their x stroke causing unintentional uneven-bevel-working. I have tried lots of goofy things that all work fine but I also know how to hone. If you don’t have so much experience then even using dead flat synth stones can be challenging.

It’s all just metal and rocks or other harder abrasive. It’s funny how it all works and how much better it all works as your skill improves. At some point you hit a level where most every stone you pick up can be learned or made to work and few razors, no matter how wonky, are not such a challenge. Which circles back to the fact that the hard to calculate convexity and differences in equipment just don’t result in anything appreciable……except for the fun in experimentation maybe.

I am mostly a exec type guy these days (directing global product development like your name actually), but once upon a time was more of an applied PhD scientist and used to love this expression: “Once again reality is #%*ing up my theory” I think of this a lot on all these convex type posts.

 

[global_dev]

I think you will understand if you try it. Getting a consistent bevel angle is not straight forward. You may end with a convex bevel instead of concave one.

Just to be clear, we’re talking spherical? I know the title is lengthwise, so i dont want to stray too far.

Most of my razors have a smiling edge, whether super slight or more pronounced. But typically not dead flat

So, when you get into the theory of honing on theoretical 30’ diameter

Wasnt the diameter something like 75’ , so even less? Not arguing, just managing expec

it could be screwed up easily if someone didn’t have smooth motion in their x stroke causing unintentional uneven-bevel-working.

if this is about lengthwise, i’d imagine you are correct. Spherical, to my mind, would be similar to a rolling x stroke in smooth motion requirements.

It’s all just metal and rocks or other harder abrasive. It’s funny how it all works and how much better it all works as your skill improves. At some point you hit a level where most every stone you pick up can be learned or made to work and few razors, no matter how wonky, are not such a challenge.

Absolutely on same page. Maybe they’ll be a point i lose interest in the “what’s next”

 

[*stefan*]

,@LJS
You are taking gibberish.
I'm not writing this because I believe that you are all wrong but because I just bought a flattening plate.
Don't you understand we need a reason to use all hones and our cheap Chinese USB-microscope( or expensive)?

Anyway there is nothing wrong with wanting to understand theory and to do testing.
The seasoned honer got skilled by honing a lot, with time likely with both planar, convex and concave hones, just as you write.

I really like this:
“Once again reality is #%*ing up my theory”

But now if we make a "circular hone" with rather small lengthwise radius and use it for bevel setting a wedge grinded blade and then progress to flat hone. Easier or harder to reach shaving Nirvana?

One may start at one end for understanding and ending up with a solution for something else.

And if progressing from a lengthwise convex hone to a flat finisher helps dealing with a blade that otherwise will not hold an edge I want that knowledge. Or just to speed up endresult on a very slow finisher.

 

[JPO]

Just to be clear, we’re talking spherical? I know the title is lengthwise, so i dont want to stray too far.

Most of my razors have a smiling edge, whether super slight or more pronounced. But typically not dead flat




Wasnt the diameter something like 75’ , so even less? Not arguing, just managing expec



if this is about lengthwise, i’d imagine you are correct. Spherical, to my mind, would be similar to a rolling x stroke in smooth motion requirements.



Absolutely on same page. Maybe they’ll be a point i lose interest in the “what’s next”

some of my stones are convex, which means convex (curved around two axis).
This is how i may use them. Usually i only use two stones, one of them are convex. I start with the coticule, which has a radius of approx 1.5 m. I start with slurry, and i hone with a slight skew angle relative to the longitudinal axis. When you do that the apex will not be touching the stone, only the bevel shoulder. i finish on that stone with water using a more perpendicular stroke. Now the apex starts to get contact. i strop the razor and do a hanging hair test, to see if it cuts arm hair mid way. This is typically a little below what i like to shave with. To bump up the edge i use either a flat jnat or a shapton gs 0.44 micron. If the latter is used i only do 5-7 strokes to get a totally silent hht. Because i am only contacting a smaller part of the bevel, the process speeds up, and you end up with a cleaner bevel. The same principle is used in knife sharpening to remove the burr. The difference is how you manipulate the bevel angle.
You are shaping the bevel from the shoulder down to the apex.
I have worked over five years with fracture mechanics and fatigue. To me it makes sense to not stress the apex more then it needs to. To me the concave bevel part is a dead end, and is not that important. If a convex stone is used incorrectly the end result is an uneven convex bevel with a more obtuse apex. So the stroke used is really important. All the focus seems to be on the wheel shape which is the least important factor.
I also have a coticule with a bigger radius i might put in between the finisher.

 

[global_dev]

Using a marker to see if there is no contact on the lower area of the bevel closest to the edge.
Suspect it will be difficult to show this with photos but always fun with pictures if you manage.

If yes on above, what does it look like after 5, 10, or 15 laps. Is it very fast to reach the outer bevel area?

Besides that I find it interesting how it shaves. But that's of course also a question of personal preference.

photos unnecessary.. I took a bevel from a flat 8K & 12K shapton kuromaku ceramics. sharpies up the edge and then in under 3 laps on the GS7 0.85, the sharpie was already gone. iirc, the convexity of my hones is subtle, but easily viewable by eye, using a glass plate I made last year for ease of consistency.

perhaps a jump from lower grit like 3-5K to .44 micron or fine ark would show the progression more slowly.

 

[*stefan*]

photos unnecessary.. I took a bevel from a flat 8K & 12K shapton kuromaku ceramics. sharpies up the edge and then in under 3 laps on the GS7 0.85, the sharpie was already gone. iirc, the convexity of my hones is subtle, but easily viewable by eye, using a glass plate I made last year for ease of consistency.

perhaps a jump from lower grit like 3-5K to .44 micron or fine ark would show the progression more slowly.

A simple but very interesting test in my opinion.
Thanks.

 

[global_dev]

I actually tried it again this afternoon, just in case I had overlooked anything.. took the previous razor and went through an entire progression from 1K through 12K flat, then to a convex zulu grey.. same results. that was kind of surprising given that I would have thought I'd see some progression (like watching the bevel form on a near wedge) based on the speed of cutting; however the convexity diameter is pretty large, so maybe not so surprising.

I really should try a lower grit flat to very high convex finish maybe that would show some different movement.

 

[*stefan*]

The image was taken just to highlight what happens if you go from a convex hone to a flat hone. This razor is a small CV Heljestrand MK 4. The image does not reflect a razor finished on a flat shapton. It was honed on a convex naniwa 3k, then it was taken to light tomo slurry on a hard shobudani jnat. This is a big jump, if you try to finish like that (it would take a really long time). What you see is that the jnat starts to reveal some of the deper 3k scratches. These cheap microscopes also tend to show a skewed reality.

The images below is from a Hart steel 1/4 holly that was honed on a convex naniwa 3k, then a convex coticule following it with a Jnat. It was finished with only 3 strokes on a shapton gs senven 0.44 micron. This is a smiling razor, which makes it a bad candidate for concex stones, but it seemed to do just fine.
Taking a picture of a mirror on the micro bevel is not easy. So you need to play with the lighting. It is also not possible to focus on the entire bevel. You might be able to do it with focus stacking software, who knows. What you do see is the micro bevel which appear dark.
I do not have any before and after pictures. Then you would need to hone the razro two times and compare. I think you will end up with the same conclusion. It is actually easier to see this in a lower resolution loupe.

The last image is from a new Wisamet super DE blade, just for reference. This is supposed to be one of the smoothest DE blades out there. If i use this in a shavette it acturally feel less smooth than the straight razor edge. Maybe that is also visible in the picture. So why does it cut so well if the apex width is the only thing that matters? To me the apex seems more obtuse then the straight razor, and it did cut better. So effecting the steel behind the apex makes sense to me.

It is probably easier to do some experimentation on your own. Geometry calculations show this quite well without any need for magnification.

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"What you see is that the jnat starts to reveal some of the deper 3k scratches. These cheap microscopes also tend to show a skewed reality".
-Thanks for clarifying, believe you, asking questions is a way to learn and get knowledge.

"So effecting the steel behind the apex makes sense to me".
-Todd at scienceofsharp seemt to take an extra interest in the last 3 micron.
"the apex of the blade must be thinned to about 100nm (one tenth of a micron) to comfortably shave facial whiskers"
-Above sentence from scienceofsharp.
He then usually looks 3 micron from the apex and wants the blade thin but also having a microconvex transition.

"Geometry calculations show this quite well without any need for magnification".
I see the same thing in the drawing sketch I made.

Thanks for the very nice pictures.

By the way, the hair that was 50 micron was from my head. Measured a whisker under the nose with the same method and it was then 90 microns.

 

[*stefan*]

I actually tried it again this afternoon, just in case I had overlooked anything.. took the previous razor and went through an entire progression from 1K through 12K flat, then to a convex zulu grey.. same results. that was kind of surprising given that I would have thought I'd see some progression (like watching the bevel form on a near wedge) based on the speed of cutting; however the convexity diameter is pretty large, so maybe not so surprising.

I really should try a lower grit flat to very high convex finish maybe that would show some different movement.

I think I will do some testing with hollow blades on flat stones just altering the torque after making the bevel and see what that will show.

,@JPO You use very heavily convex stones? Could you take a picture with a straight ruler on top of one?

 

[global_dev]

I think you will understand if you try it. Getting a consistent bevel angle is not straight forward. You may end with a convex bevel instead of concave one.

i could really use some sketches to better understand how i would end up with a convex bevel. if my sphere is a sphere, it shouldn't matter the angle of "attack" skew for lack of better terminology on my part.

 

[JPO]

i could really use some sketches to better understand how i would end up with a convex bevel. if my sphere is a sphere, it shouldn't matter the angle of "attack" skew for lack of better terminology on my part.

All i know is that my practical experience tells me that it is not that simple. To follow a curvature you would also need to adjust your angle along the short axis constantly, which i am not that good at. You may end up with enough variance to negate the effect of a big wheel radius. There is a reason why the German grinders only worked on a smaller part of the stone around the middle.
The distance AL and AB is different. If you in addition to this add some skew angle it starts to get interesting.
If you use a marker on the spine and on the bevel you might be able to see what your stroke is doing to the razor. Look at the swarf on the stone. You can probably try to calculate this, but an practical approach is probably easier.

 

[JPO]

I think I will do some testing with hollow blades on flat stones just altering the torque after making the bevel and see what that will show.

,@JPO You use very heavily convex stones? Could you take a picture with a straight ruler on top of one?

They all have a different radius. I start with a small radius and transition to a bigger radius, ending on a flat stone.
The key is the bevel shaping stone.

I think if you have only played with stone of say 20 ft, you are missing out. The edge does feel different. You will not figure this out behind a keyboard, you need to get your feet wet

 

[JPO]

i could really use some sketches to better understand how i would end up with a convex bevel. if my sphere is a sphere, it shouldn't matter the angle of "attack" skew for lack of better terminology on my part.

Maybe this sketch is easier. You see the difference in length of the red and the green arrow.

 

[*stefan*]

They all have a different radius. I start with a small radius and transition to a bigger radius, ending on a flat stone.
The key is the bevel shaping stone.

I think if you have only played with stone of say 20 ft, you are missing out. The edge does feel different. You will not figure this out behind a keyboard, you need to get your feet wet

Thanks, nice picture.
This is new to me and interesting.

Guess you right about it needs to be tested to determine how good edges it gives.
So you will send your stones to me and I can test it?

 

[JPO]

Thanks, nice picture.
This is new to me and interesting.

Guess you right about it needs to be tested to determine how good edges it gives.
So you will send your stones to me and I can test it?

This is from an 175 year old German text book. It was translated by a member on a German shaving forum.

Polytechnische Mittheilungen, Volum 3, Page 28 and 29

A well-versed man in this matter (honing razors) told me of this for him very advantageous practice: The first, sharpest/best biting/roughest stone (which can be an oil or water stone) shall be made to a convex surface. The second stone in the arsenal, which is a levantinian oilstone that word does not really exist anymore/is a negatively connoted word.. so it should better be called stone from the orient or an arabic one from syria/lebanon/jordan etc. shall be prepared in the same way, even though with less convexness; only the third (last) stone shall be flat, and for this one a fine hard clay slate stone (blue sharpening stone) shall be chosen, here the honing shall always be done with water only. This method is rational; with the convexness of the first two stones the steel near the bevel will be thinned down successively, which only leads to a superbly thin bevel with the last stone, who only needs very little work to do so: I have my doubts, as this method of honing on convex stones requires more experience than even the undoubtful experience needing process of honing on flat stones. As a matter of fact this process, as far as I know, is only used by knifemakers, knivegrinders and barbers. so basically he tells us, that we normal dudes do not know enough/have not had the years of training required to hone on convex stones

 

[global_dev]

All i know is that my practical experience tells me that it is not that simple. To follow a curvature you would also need to adjust your angle along the short axis constantly, which i am not that good at. You may end up with enough variance to negate the effect of a big wheel radius. There is a reason why the German grinders only worked on a smaller part of the stone around the middle.
The distance AL and AB is different. If you in addition to this add some skew angle it starts to get interesting.
If you use a marker on the spine and on the bevel you might be able to see what your stroke is doing to the razor. Look at the swarf on the stone. You can probably try to calculate this, but an practical approach is probably easier.


View attachment 1335716View attachment 1335718
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i had to look up orthrodrome/loxodrome and sailing/mercator maps and not sure how it applies to honing on a sphere.

if I understand (and i most probably incorrect) the most simplistic premise behind the convexity argument, there are 2 points touching the sphere at all times. No matter how you turn your sphere those 2 points should touch in the “same” length with a “similar” sphere volume under those 2 points . The distance wont get longer or shorter in practice, and the which appears very different from the mercator map projection deformation at the poles.

To a “different” matter in same realm, as you move both points along the length of the spine/edge on the sphere, technically, if you did it correctly, you would have similar lengths of distance between the 2 corresponding points as you move along. Theoretically the same argument as the previous paragraph.

Maybe i dont understand the skew argument well enough. please feel free to point out the flaws in my understanding, i am very much open to criticism of my current understanding, i am not an engineer or navigator.

 

[JPO]

i had to look up orthrodrome/loxodrome and sailing/mercator maps and not sure how it applies to honing on a sphere.

if I understand (and i most probably incorrect) the most simplistic premise behind the convexity argument, there are 2 points touching the sphere at all times. No matter how you turn your sphere those 2 points should touch in the “same” length with a “similar” sphere volume under those 2 points . The distance wont get longer or shorter in practice, and the which appears very different from the mercator map projection deformation at the poles.

To a “different” matter in same realm, as you move both points along the length of the spine/edge on the sphere, technically, if you did it correctly, you would have similar lengths of distance between the 2 corresponding points as you move along. Theoretically the same argument as the previous paragraph.

Maybe i dont understand the skew argument well enough. please feel free to point out the flaws in my understanding, i am very much open to criticism of my current understanding, i am not an engineer or navigator.

If your blade remain perfectly normal to the curvature of the stone this is correct, but i am not perfect, so if you deviate from that angle during the stroke the two contact points will move by an unequal amount on the apex and on the spine.
The easiest way to test it is if you use a convex stone. Start with a 45 deg heel leading stroke until the bevel is set. Then you start with a perpendicular stroke. You will now feel the blade starts to stick. This is because the apex is now getting better contact. It will all make sense if you try it in practice.

 

[global_dev]

Maybe this sketch is easier. You see the difference in length of the red and the green arrow.
View attachment 1335742

in this sketch, while pretty unclear to m in terms of what i should really take away, if the distance of an actual hollow of razor point A on edge and point B on spine could not at the same time be equivalent to the green or red line. If you rotate A around B wouldnt that distance always be the same?

Theoretically if there was no friction and metal removal, if you skew the razor by 45°, what did I effectively change? I could rotate that picture in 3D space and wouldnt it be the same?

in reality, the decrease in each point pair changes as the metal goes away, and I guess user error in keeping the same “level”,however it feels kinda moot.

i will try to take some pics of what i think i see

 

[global_dev]

playing around in the space, since the curvature of the surface is equal between the 2 contact dots, isnt the distance the same? Or are you saying that on the right pic, the edge dot is no longer the point of contact or its effectively changing the bevel angle as i sweep from the left to the right continuously moving along the length of the edge/spine?

 

[JPO]

View attachment 1336064

playing around in the space, since the curvature of the surface is equal between the 2 contact dots, isnt the distance the same? Or are you saying that on the right pic, the edge dot is no longer the point of contact or its effectively changing the bevel angle as i sweep from the left to the right continuously moving along the length of the edge/spine?

If you now rotate around those contact points by lifting the tang a little, the contact points changes an unequal amount. This is enough to make a difference.