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Lengthwise convex hone

I wanted to know what it looks like taking a blade honed on a flat stone and then progressing with it to a lengthwise convex hone.

I used my Naniwa flattening plate to measure it's lengthwise convexity that I got to be
0,3mm on a distance of 250mm.

Then created the corresponding convexity in 2D.

And it looks like that only the rear of the bevel makes contact with the hone initially. There will in this case be a gap of 6 micron between the edge and hone. This means there will first be polishing of the top area of bevel and when the material being honed away all of the bevel will contact.
Probably rather fast. If this is correct it could be tested with a marker pen before hopning on convex hone. Anyone tested?

If it's an advantage I guess needs to be tested by practice.

Convex_1.GIFConvex_2.GIFConvex_3.GIF
 
I think I understand what you are asking & i think you are right, the marker should show what you described.

It makes sense to me to get the concave action from the convex hones somewhere before the polishing/finishing stage, it’s not a difficult test.

what type of advantage are you looking for? Performance, longevity, convenience?
 
I prefer a narrow hone to a sidewise convex hone.
The Naniwa flattening stone is only being used to kitchen knives sharpening stones.

Just like to analyse things and wanted to see what it looks like putting a blade on a lengthwise
Convex finishing hone from a geometric viewpoint.

I'm curious about if there could be any advantage or disadvantages of ending the honing on a lengthwise convex hone.
But not using it for razors myself at this point.
 
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I can take a razor from a flat 5k to a convex ~.8 g7 over the next couple of days and take some simple pics and notes.

anything in particular/specific you want me to observe and take notes on?
 
I wanted to know what it looks like taking a blade honed on a flat stone and then progressing with it to a lengthwise convex hone.

I used my Naniwa flattening plate to measure it's lengthwise convexity that I got to be
0,3mm on a distance of 250mm.

Then created the corresponding convexity in 2D.

And it looks like that only the rear of the bevel makes contact with the hone initially. There will in this case be a gap of 6 micron between the edge and hone. This means there will first be polishing of the top area of bevel and when the material being honed away all of the bevel will contact.
Probably rather fast. If this is correct it could be tested with a marker pen before hopning on convex hone. Anyone tested?

If it's an advantage I guess needs to be tested by practice.

View attachment 1333173View attachment 1333174View attachment 1333175
I played a little with different convex stones, but you are only referring to a wheel shaped stone. You are able to see it with a loupe, but if you remove 0.3 mm on a Naniwa stone, you end up with a radius of 60 ft (18.5 m). On a 7/8 razor this is 0.017 micron difference in the middle of the bevel. So if you compare it to a human hair you need to divide it by 5854 times.
It starts to get more interesting when you use a smaller wheel radius, and you put in a curvature on the short axis as well.
But even then inconsistency in your stroke can easily negate any benefit.
The skew angle relative to the longitudinal axis is more important then the radius, if you make the stone convex.
A skew angle of 20 deg can be enough to change the angle 1 deg (equivalent to one layer of tape). This is because the contact point on the bevel and the spine changes. It may not be intuitive, but you can see it if you use a marker or a microscope.
You need a radius of less then 2 meters to start to see any benefit, and even then it is marginal. If a convex stone is used incorrectly you may actually end up with the opposite effect, ie. a convex bevel instead of a concave bevel. By only shaping the stone lengthwise you would avoid that.
Here is how it looks like if you put in some concavity in the bevel and finish with a flat hone. Your last stone only need to work on a smaller part of the bevel, like adding a layer of tape without the tape:)

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I can take a razor from a flat 5k to a convex ~.8 g7 over the next couple of days and take some simple pics and notes.

anything in particular/specific you want me to observe and take notes on?
To me one interesting observation is how the bevel angle changed by using different strokes. There is a reason why the old German grinders only used the middle of the convex stone, with sort of a wind shield wiper motion. You are then able to work on different sections of the bevel just by varying the skew angle. They call it thinning. Then they move on the a flat finisher to establish a clean apex. It also makes the last stone more efficient.
 
I can take a razor from a flat 5k to a convex ~.8 g7 over the next couple of days and take some simple pics and notes.

anything in particular/specific you want me to observe and take notes on?


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?

The result would vary with honing load/torque and hone of course so no exact amount of laps necessary but the first 5 laps is perhaps extra intressant.

Probably the width of the bevel will increase a little.
Besides that I find it interesting how it shaves. But that's of course also a question of personal preference.
 
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?

The result would vary with honing load/torque and hone of course so no exact amount of laps necessary but the first 5 laps is perhaps extra intressant.

Probably the width of the bevel will increase a little.
Besides that I find it interesting how it shaves. But that's of course also a question of personal preference.
I erased the concave bevel effect on a 7/8 razor that was shaped with a convex hone with a radius of 1.5 m, using a 0.44 micron shapton gs senven after 5 strokes. You will probably only need one or two strokes before you make contact with the apex.
 
I played a little with different convex stones, but you are only referring to a wheel shaped stone. You are able to see it with a loupe, but if you remove 0.3 mm on a Naniwa stone, you end up with a radius of 60 ft (18.5 m). On a 7/8 razor this is 0.017 micron difference in the middle of the bevel. So if you compare it to a human hair you need to divide it by 5854 times.
It starts to get more interesting when you use a smaller wheel radius, and you put in a curvature on the short axis as well.
But even then inconsistency in your stroke can easily negate any benefit.
The skew angle relative to the longitudinal axis is more important then the radius, if you make the stone convex.
A skew angle of 20 deg can be enough to change the angle 1 deg (equivalent to one layer of tape). This is because the contact point on the bevel and the spine changes. It may not be intuitive, but you can see it if you use a marker or a microscope.
You need a radius of less then 2 meters to start to see any benefit, and even then it is marginal. If a convex stone is used incorrectly you may actually end up with the opposite effect, ie. a convex bevel instead of a concave bevel. By only shaping the stone lengthwise you would avoid that.
Here is how it looks like if you put in some concavity in the bevel and finish with a flat hone. Your last stone only need to work on a smaller part of the bevel, like adding a layer of tape without the tape:)

View attachment 1333388

View attachment 1333383
View attachment 1333386

"but you are only referring to a wheel shaped stone".
-Yes you are correct.
-I ended up with a radius of 17,6 m

"On a 7/8 razor this is 0.017 micron difference in the middle of the bevel. So if you compare it to a human hair you need to divide it by 5854 times".
-I got the largest "deviation" between a flat vs. the circular hone in the middle of the blade where it does not contact, 0,0197mm.
In the bevel area I got a distance in the front of the bevel( the edge) of 6 micron to the circular hone.

A human hair is somewhere between 17-100 micron?

"Here is how it looks like if you put in some concavity in the bevel and finish with a flat hone. Your last stone only need to work on a smaller part of the bevel, like adding a layer of tape without the tape".
-I guess that's correct. But if it's better.....

Another thing is the torque being used. If using higher torqe on a thin hollow razor that deflect on a flat stone, moving on to another flat higher grit stone using less torque I think the effect will be similar as moving from flat to convex hone.
 
"but you are only referring to a wheel shaped stone".
-Yes you are correct.
-I ended up with a radius of 17,6 m

"On a 7/8 razor this is 0.017 micron difference in the middle of the bevel. So if you compare it to a human hair you need to divide it by 5854 times".
-I got the largest "deviation" between a flat vs. the circular hone in the middle of the blade where it does not contact, 0,0197mm.
In the bevel area I got a distance in the front of the bevel( the edge) of 6 micron to the circular hone.

A human hair is somewhere between 17-100 micron?

"Here is how it looks like if you put in some concavity in the bevel and finish with a flat hone. Your last stone only need to work on a smaller part of the bevel, like adding a layer of tape without the tape".
-I guess that's correct. .....

Another thing is the torque being used. If using higher torqe on a thin hollow razor that deflect on a flat stone, moving on to another flat higher grit stone using less torque I think the effect will be similar as moving from flat to convex hone.
A human hair is around 80-100 microns.
These flexible grinds does complicate things. You can basically achieve some of the same effects on a flat stone by varying the torque. To much torque or pressure lifts the apex of the stone.
Is it better? In the right hands it can be better, but there is allot of variables that complicates things.
It can be part of a solution if you are dealing with geometry issues in the razor.
I recently tried to hone an extra hollow ground böker razor using convex stones. The edge got to weak, and i was not able to finish it well. You need enough support behind the edge to be able to cut the steel.
If someone is telling you it is better they are not telling you the whole story.
you are shaving with the apex. What happens behind that apex can make a difference, but if you need it, that is highly subjective.
Just one more tool.
 
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I measured mine hair to 50 microns with a micrometer but it is difficult as the hair wants to deform.

We're now also getting into the thickness of the bevel. Then the questions: what honing angle is to prefer, edge trailing strokes thin the bevel( but also create a burr) is also in the mix.
I like honing, one can keep it simple but also try understanding things in theory. Testing is however always needed.

Perhaps a lengthwise circular or convex hone might work very nice for thinning out the bevel. If getting a wedge and having issues reaching the bevel, using a convex hone in bevel set could help? And after bevel set adding tape to the spine if needed.
 
If you hone on a convex surface with a slight skew angle on you blade you are able to affect the bevel angle. You ensure proper apex contact and a small micro bevel by finishing on a flat stone. Thank you for the model of the razor profile:) The same affect as a high angle stroke to remove a burr on a knife. The same principle should apply to get a cleaner apex.

1632491148071.png
 
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?

The result would vary with honing load/torque and hone of course so no exact amount of laps necessary but the first 5 laps is perhaps extra intressant.

Probably the width of the bevel will increase a little.
Besides that I find it interesting how it shaves. But that's of course also a question of personal preference.

my hones have convexity length and width-wise. i'll see if my usb microscope works still. not as good a setup as ekretz and the rest of the scope guys.
 
"Here is how it looks like if you put in some concavity in the bevel and finish with a flat hone. Your last stone only need to work on a smaller part of the bevel, like adding a layer of tape without the tape:)".

"I erased the concave bevel effect on a 7/8 razor that was shaped with a convex hone with a radius of 1.5 m, using a 0.44 micron shapton gs senven after 5 strokes. You will probably only need one or two strokes before you make contact with the apex"

Bevel Convec to flat.GIF.

,@JPO It actually looks like the opposite to me in this picture. But I find it easy to get fooled watching bevels.
Do you have a "pre picture" before taking the blade to the 0.44 micron shapton gs ?

What type of hone was the convex one used?
 
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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If you hone enough razors on enough stones you will eventually realize how all this theory is wasted on the reality of it all not meaning much. At least you are having fun learning!
 
If you hone enough razors on enough stones you will eventually realize how all this theory is wasted on the reality of it all not meaning much. At least you are having fun learning!

i can agree to a point about the reality; 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 wasn’t aware of this, why would smiling edges be bad candidates for convex hones?
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 can agree to a point about the reality; 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. We are also not considering that this was a common approach over hundred year ago.
 
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