polishing: blade geometry

[noj]

I have a knife whose wide bevel I am attempting to shape, prior to polishing. To be more precise, I wish to remove the high (low) spots, and of course have smooth transitions (in blade curvature).

Using course stones (or sandpaper), I am using shiny spots (burnishing) as indicators of high spots, and non-removal of previous scratches (often also dark spots) as indicators of low spots.

I have found some issues I haven't been able solve. Advise, comments, questions welcome.

I get the scratch patterns seemingly looking good, but at higher grit, the high (low) spots become visible again. After many repeats, this becomes frustrating, time-consuming, and wondering if I am making progress. Sometimes I wonder if my work is creating new low spots. I have been as careful as I know how to keep the stones flat and clean. I have ground enough metal away that the shinogi has changed; does that tend to imply I need to remove metal at the edge? I am not sure what to look for, try next, or exactly what to ask.

Thanks!

I have spent a lot of time on this, so it's not like I spent an hour and gave up;-)

 

[OkayMode]

Sounds like you’re not removing the low spots entirely at the lower grits, which then becomes apparent when you move higher - it’s frustrating for sure.

Are you using alternating scratch patterns between each stone to help you see your work?

You mention you’re raising your shinogi - where are you applying pressure?

 

[ethompson]

Pictures are worth thousand words in this case, would be very helpful in diagnosis and recommendation

 

[ian]

Maybe make sure to check your bevel geometry on something hard like a hard, clean (no slurry) stone or clean sandpaper before moving up? A lot of times coarser grit stones are muddier and can hide low spots more than higher grit stones.

 

[Choppin]

Maybe make sure to check your bevel geometry on something hard like a hard, clean (no slurry) stone or clean sandpaper before moving up? A lot of times coarser grit stones are muddier and can hide low spots more than higher grit stones.

That's what I'm thinking as well... what stones are you using?

 

[ReiHamono]

Post some pictures with the scratch pattern all in the same direction under some fluorescent or LED lighting to display it the best

No slurry, show a macro of all the edges also

 

[KenjiF]

There are some stones that are better at identifying low spots. the chosera 3k is my choice for this as it will burnish (make shiny) the highs and darken the lows. I'll use it after setting geometry on a 400 stone just to check if I'm close. You can also color in the whole bevel with a sharpie and that will pretty accurately show you low spots in the beginning. Sandpaper works as well but it will be opposite where the shiny (sandpaper finish) that remains after you put it to the stone will be the low spots.

Another thing to keep in mind is that coarse stones tend to be softer (unless your using a diamond stone) so will reach more spots (the lows) than your harder fine stones. I like soft stones because they tend to be fast but I like to use a harder stone early on in the progression (under 1k) to avoid surprises later on. Ill us a SG500 or hard diamond stone.

I would alternate scratch patterns but I would keep them parallel (or close to parallel) scratch patterns and a 45-degree scratch pattern at the start. 90 degree polishing edge or spine facing away from you will remove a lot of material quickly and can be great if you are positive that material needs to be removed but it will mean less of the bevel is making contact with the stone so you can reach spots that you won't be able to hit with parallel polishing later (especially the shinogi line) and it's easier to grind in lows. This is much easier if you are swapping hands for different sides.

For the shinogi I personally like to put less pressure on it on the coarser softer stones and more pressure as the stones get harder and finer. This way I can avoid over-grinding the shinogi line with scratches I can't get out later on. If the cutting edge bevel is in a good place (nail flexing thin if you like that) or already at zero (cutting bevel is gone and you will start to raise a burr as you thin) don't touch it. You are just unnecessarily losing height on your knife. If there is a low right at the cutting edge then first check it's straight (you will usually have a high on one side and a corresponding low on the other side if there is a bend), If its straight then you have to make the call if its worth fixing. Super common at the heel.

As @ethompson said pics will make it much easier to help.

Last thing to check (actually the first thing you should check) is if the blade is straight. If you bent it between sessions then you will see new lows. I've done this before on thin knives and now if I do a knife over multiple sessions I'll check its straightness before each session.

I've been there and feel your pain mate.

 

[Choppin]

There are some stones that are better at identifying low spots. the chosera 3k is my choice for this as it will burnish (make shiny) the highs and darken the lows. I'll use it after setting geometry on a 400 stone just to check if I'm close. You can also color in the whole bevel with a sharpie and that will pretty accurately show you low spots in the beginning. Sandpaper works as well but it will be opposite where the shiny (sandpaper finish) that remains after you put it to the stone will be the low spots.

Another thing to keep in mind is that coarse stones tend to be softer (unless your using a diamond stone) so will reach more spots (the lows) than your harder fine stones. I like soft stones because they tend to be fast but I like to use a harder stone early on in the progression (under 1k) to avoid surprises later on. Ill us a SG500 or hard diamond stone.

I would alternate scratch patterns but I would keep them parallel (or close to parallel) scratch patterns and a 45-degree scratch pattern at the start. 90 degree polishing edge or spine facing away from you will remove a lot of material quickly and can be great if you are positive that material needs to be removed but it will mean less of the bevel is making contact with the stone so you can reach spots that you won't be able to hit with parallel polishing later (especially the shinogi line) and it's easier to grind in lows. This is much easier if you are swapping hands for different sides.

For the shinogi I personally like to put less pressure on it on the coarser softer stones and more pressure as the stones get harder and finer. This way I can avoid over-grinding the shinogi line with scratches I can't get out later on. If the cutting edge bevel is in a good place (nail flexing thin if you like that) or already at zero (cutting bevel is gone and you will start to raise a burr as you thin) don't touch it. You are just unnecessarily losing height on your knife. If there is a low right at the cutting edge then first check it's straight (you will usually have a high on one side and a corresponding low on the other side if there is a bend), If its straight then you have to make the call if its worth fixing. Super common at the heel.

As @ethompson said pics will make it much easier to help.

Last thing to check (actually the first thing you should check) is if the blade is straight. If you bent it between sessions then you will see new lows. I've done this before on thin knives and now if I do a knife over multiple sessions I'll check its straightness before each session.

I've been there and feel your pain mate.

Shapton Glass stones are great for checking the bevels as you thin - I use SG500 and SG2000 after my 200 grit thinning stone. hard, non-muddy stones like them will let you know exactly where you are grinding.

 

[noj]

Thanks to everyone who took the time to reply! Sorry to take so long, but I have a couple things occupying my time.

About photos, my cameras don't seem to take photos that look anything like what I see on the forum. Often I can get a completely different look of the same thing with different lighting/angles. Should I get a photo of things are they are, only after a course stone, or both? I am using LED light, and tried camera, and a LUMIX. Both have issues with auto focus; I am guessing they are looking for faces. Right now, it was finished on finer stones, however imperfectly.

I have used sharpie for edges, but for polishing it seems to create a sicky mess on the stone. I let the ink completely dry.

How to you alternate 45 degree scratch patterns? Link to any videos? I can imagine changing the angle in the same hand, or switching sides with the edge facing forward. Both seem awkward.

About where I (try to) apply pressure, it's where I want to remove metal. For shaping/geometry, I aim for the shiny (high) spots. In practice, I often have a hard time removing core steel at the same rate as the cladding. My last session with this knife, I think I got closer to doing it right. It's nicely TBE, and the bevel angle on the hagane is a tad higher relative to the cladding, if that's the right thing to do.

About detecting blade straightness, I have no clue. I hold it and (think) I look at it the way I have seen described (usually very little detail), and I can't tell.

Yes, I will post pictures as soon as I have time!

 

[noj]

That's what I'm thinking as well... what stones are you using?

Tried a bunch of things over time - story for later maybe. The last session was a King 300, and checked on Shapton Pro 1000. Sometimes the issues showed up more clearly on Chosera 3000 afterward.

 

[KenjiF]

Tried a bunch of things over time - story for later maybe. The last session was a King 300, and checked on Shapton Pro 1000. Sometimes the issues showed up more clearly on Chosera 3000 afterward.

Yeah I have never hit the chosera 3k without having to go back and fix a scratch or spot I missed… yet. If you can get it all one consistent burnish on a 3k chosera then you know you’re in a good place.

Here is the master at work @naader on the 3k.


Sorry if I want clear before. I alternate scratch patterns parallel with the edge (lots of the bevel is in contact) and 45 degrees. To alternate 45 degree you would have to switch hands or hold the knife w tip facing towards you (never tried but both sound uncomfortable). I’ll switch sides when I switch bevels. Spine is always facing away or off the side of the stone. @milangravier videos on Instagram/YouTube are GREAT for blade geometry.

For blade straightness the best way I have found is to sight down the cutting edge and the spine with the knife backlit (looking into a light source) it creates a silhouette and you can see where the bends are. You will get better at this as you do it more. To begin with I had a straight edge I would sight down first to know what straight looked like then pick up my knife.

Here’s a good video about how to check if something is straight.

 

[noj]

There are various issues, and photography was tricky, so let me start just at the heel. The finish is relatively fine, and been lightly used in kitchen. I asked about whether to go back on course stones before taking pictures, but no reply yet. The scratch patterns are mixed, at least in part because I tried hiding some stuff with finger-stones, and the low spots. I took more than one picture of the same area because I see different things depending on angle/lighting. With some feedback, I can reduce the photo clutter in the future.

 

[noj]

Sounds like you’re not removing the low spots entirely at the lower grits, which then becomes apparent when you move higher - it’s frustrating for sure.

Are you using alternating scratch patterns between each stone to help you see your work?

You mention you’re raising your shinogi - where are you applying pressure?

There are still low spots, even after many hours of work, and multiple attempts over a few years.

I am using alternating scratch patterns. I have been following what I have seen in the MG videos.

[cut and paste from above]
About where I (try to) apply pressure, it's where I want to remove metal. For shaping/geometry, I aim for the shiny (high) spots. In practice, I often have a hard time removing core steel at the same rate as the cladding. My last session with this knife, I think I got closer to doing it right. It's nicely TBE, and the bevel angle on the hagane is a tad higher relative to the cladding, if that's the right thing to do.

 

[noj]

Pictures are worth thousand words in this case, would be very helpful in diagnosis and recommendation

See photos I just posted. They are only for the heel, and same side/heel. Once I get a better feel for what photos you find useful (grind/camera technique), I can cover more blade, and less "copies" of the same thing.

 

[noj]

Maybe make sure to check your bevel geometry on something hard like a hard, clean (no slurry) stone or clean sandpaper before moving up? A lot of times coarser grit stones are muddier and can hide low spots more than higher grit stones.

They fail my test rather early. The last session was a King 300, and checked on Shapton Pro 1000. Sometimes the issues showed up more clearly on Chosera 3000 afterward.

 

[noj]

Post some pictures with the scratch pattern all in the same direction under some fluorescent or LED lighting to display it the best

No slurry, show a macro of all the edges also

Some pictures downloaded. Getting scratch pattern all in the same direction will have to wait for me to redo from course grit. What grits should I get pictures from (the course, or higher grit where I check, or both)?

 

[noj]

Yeah I have never hit the chosera 3k without having to go back and fix a scratch or spot I missed… yet. If you can get it all one consistent burnish on a 3k chosera then you know you’re in a good place.

Here is the master at work @naader on the 3k.


Sorry if I want clear before. I alternate scratch patterns parallel with the edge (lots of the bevel is in contact) and 45 degrees. To alternate 45 degree you would have to switch hands or hold the knife w tip facing towards you (never tried but both sound uncomfortable). I’ll switch sides when I switch bevels. Spine is always facing away or off the side of the stone. @milangravier videos on Instagram/YouTube are GREAT for blade geometry.

For blade straightness the best way I have found is to sight down the cutting edge and the spine with the knife backlit (looking into a light source) it creates a silhouette and you can see where the bends are. You will get better at this as you do it more. To begin with I had a straight edge I would sight down first to know what straight looked like then pick up my knife.

Here’s a good video about how to check if something is straight.

On the topic of detecting issues with straightness, I want to make sure I understood what you said. I watched the video, and can see what is done, with a key missing ingredient: what exactly is he looking for. When I use the visual technique, if I look at just the profile, the blade almost disappears into the background, and it's essentially impossible to hold it steady enough to get a "perfect" profile. Holding it a tiny bit to the side, I can see (expected) blade curvature, especially if I get reflections from a known background (window screen, etc.). This might get tricky if the blade is naturally convex (viewed from heel to tip), but is warped so it becomes flat, and the other side is naturally flat, but only looks convex because it's warped. Anyhow, I am "looking" but I don't know how to look .. yet;-)

 

[KenjiF]

So seeing ‘straight’ does take a minute to learn but let me give you a few tips that worked for me…

Point into a light source. I actually find a white wall that’s bouncing light to be a good source. Better if you don’t have a bunch stuff going on in the background to begin with. A white sheet over a window with no other light sources would probably be the best bet. The closer the knife is to your eye the less of the blade will be in focus so you actually want to hold it away from your face to begin with. Longer the blade the further I’ll hold it away. Focus your eye one the part of the edge or spine that is closest to you and slowly run your eye up the edge or spine as you lift the handle up (for a curved blade) the background is light and the edge is in shadow so you should be seeing a lot of contrast. A bent knife will curve one way or the other or have waves in it. You get better and will start noticing micro bends as you get better at it.

Can’t tell what’s high and low from those photos. Put it on a harder stone like the chosera 3k and do a few pass at 45 degrees and you should see enough contrast to tell what’s high and low. Take pictures then we can help. Lighting is fine.

Bevel looks thin enough so I wouldn’t be taking more material from there unless I needed to (you will just be loosing height).

Is that a togashi for hitohira? If so I was just working on one and the cladding was tough to burnish on the chosera 3k.

I have a knife that I’m working on that has some lows so I’ll take a pic and post it here when I get a chance as reference.

 

[KenjiF]

Ok here is a pretty good example of a bend and how it will show up on bevel when polishing…

Looking down the edge I could see a pretty big bend.

Only the choil is in focus the blurry part is the rest of the edge up to the tip. I’ve tilted the knife so you can see up to tip. You can see it’s bending towards the right. The spine is bent the same way but less so. I put the left bevel (if the edge is pointing up like image) on a 3k chosera and expect to see a high spot on that side (the low spot will be on the opposite side).

Yup as expected it right there. The line is the angle the bend is. It’s hard to tell from the image but the bend is not actually perpendicular to edge it’s slightly angles.

I line up my bending stick with that line and bend the opposite way and keep checking till it looks straight.

Back on the 3k and I see this…

So much better but still a small high spot. I check the other bevel on stones and it’s dead flat. If there was a corresponding low then I could give it a little tap with a brass hammer but in this case if I want to get rid of it I’m going to have to grind.

If I didn’t check it was straight I would have gone to 180 grit and ground a bunch of material to get the ‘high’ I was seeing out and the low on the opposite side. I could probably do it but as soon as I straightened the knife and put back on stones you would see I’ve ground new lows and highs.

Lmk if any of that doesn’t make sense. It took me a bit to get my head around it and I just had to be careful when I started thinning knives.

Anyone know a more reliable way of checking straight than an eyeball? I’m sure there is a good way (maybe a laser level shining down edge?) but I’m yet to test and find a better way…

 

[noj]

Ok here is a pretty good example of a bend and how it will show up on bevel when polishing…

Looking down the edge I could see a pretty big bend.

View attachment 256939

Only the choil is in focus the blurry part is the rest of the edge up to the tip. I’ve tilted the knife so you can see up to tip. You can see it’s bending towards the right. The spine is bent the same way but less so. I put the left bevel (if the edge is pointing up like image) on a 3k chosera and expect to see a high spot on that side (the low spot will be on the opposite side).

View attachment 256940

Yup as expected it right there. The line is the angle the bend is. It’s hard to tell from the image but the bend is not actually perpendicular to edge it’s slightly angles.

I line up my bending stick with that line and bend the opposite way and keep checking till it looks straight.

Back on the 3k and I see this…

View attachment 256942

So much better but still a small high spot. I check the other bevel on stones and it’s dead flat. If there was a corresponding low then I could give it a little tap with a brass hammer but in this case if I want to get rid of it I’m going to have to grind.

If I didn’t check it was straight I would have gone to 180 grit and ground a bunch of material to get the ‘high’ I was seeing out and the low on the opposite side. I could probably do it but as soon as I straightened the knife and put back on stones you would see I’ve ground new lows and highs.

Lmk if any of that doesn’t make sense. It took me a bit to get my head around it and I just had to be careful when I started thinning knives.

Anyone know a more reliable way of checking straight than an eyeball? I’m sure there is a good way (maybe a laser level shining down edge?) but I’m yet to test and find a better way…

Aha, got it, explanation wise, now I'll have to try.

It is Togashi for Hitohira. I know it's not ideal for polishing, but seemed like a place to start for bevel geometry.

I say that in part because of the mess I created when I first got it. That was several years back, and before I discovered this forum. I had asked for advice on sharpening, and was told to try a little thinning with entire wide bevel on the stone. Well, the factory finish (machined, media blasted, or whatever) hid all sorts of high/low spots. The only course stone I had at the time was a Chosera 400, and it was my first or second time working with a wide bevel.

When you said "cladding was tough to burnish on the chosera 3k", by burnish do you mean darken the cladding, especially the low spots?

The last session I had with this knife, I had just thinned, and gotten a very nice TBE, and fresh edge. I am granting myself a few days of fun in the kitchen before I take it to the stones, but I will get those pictures.

Thank you for taking the time to write this up (and photos)!

 

[KenjiF]

I actually think mine is a great blade for polishing. There was some unevenness when I got it but I am used to thinning TF’s so it all felt minor. It’s very reactive but putting some baking soda in my water fixes that. There is even some details hiding in the cladding of mine…

Burnishing is the shiny high spots. As a stone ‘glasses over’ the surface becomes smoother and if it is hard enough and there is enough pressure the steel will stop being cut as much and start compressing and moving to match the smoothness of the stone. The smoother a surface, the less light it will catch and the more reflective it will be… thus it looks shiny.

Some cladding I’ve found burnishes very easily on the 3k but this cladding required a lot of pressure (or a high spot) to see a burnish. Not sure why but that was my experience. Still useful for finding highs and lows.

 

[Rangen]

I actually think mine is a great blade for polishing. There was some unevenness when I got it but I am used to thinning TF’s so it all felt minor. It’s very reactive but putting some baking soda in my water fixes that. There is even some details hiding in the cladding of mine…

View attachment 257067

Burnishing is the shiny high spots. As a stone ‘glasses over’ the surface becomes smoother and if it is hard enough and there is enough pressure the steel will stop being cut as much and start compressing and moving to match the smoothness of the stone. The smoother a surface, the less light it will catch and the more reflective it will be… thus it looks shiny.

Some cladding I’ve found burnishes very easily on the 3k but this cladding required a lot of pressure (or a high spot) to see a burnish. Not sure why but that was my experience. Still useful for finding highs and lows.

A question. How do you and other polishers wind up with such a clean line between the cladding and the kurouchi? I can't imagine having that kind of control over a surface that's face down on a stone, and yet you must have followed your whole progression right up to that clean line.

 

[ethompson]

A question. How do you and other polishers wind up with such a clean line between the cladding and the kurouchi? I can't imagine having that kind of control over a surface that's face down on a stone, and yet you must have followed your whole progression right up to that clean line.

Mix of being patient / careful and also avoiding any manner of thick slurry that could cause the KU to erode as abrasive rides up the face

 

[KenjiF]

Mine aren’t super clean yet but as I’m moving up my progression I’ll put more pressure on the shinogi line. I’ll have my fingers further down the bevel on my soft stones because a soft stone will reach further than a hard one. By my final stones I’m putting pressure directly on shinogi line. I imagine using hard diamond stones would make this more accurate and mean you wouldn’t have to change pressure as much but I haven’t sprung for a full NSK lineup yet… do you find this @ethompson?

 

[stringer]

Mix of being patient / careful and also avoiding any manner of thick slurry that could cause the KU to erode as abrasive rides up the face

This explains why I don't get the greatest results by being impatient and careless while swimming in a puddle of muck.

 

[ethompson]

Mine aren’t super clean yet but as I’m moving up my progression I’ll put more pressure on the shinogi line. I’ll have my fingers further down the bevel on my soft stones because a soft stone will reach further than a hard one. By my final stones I’m putting pressure directly on shinogi line. I imagine using hard diamond stones would make this more accurate and mean you wouldn’t have to change pressure as much but I haven’t sprung for a full NSK lineup yet… do you find this @ethompson?

Doesn’t hurt - shapton glass or other very hard synthetics will also work. Keeping things crispy has been my biggest focus these days and I’m growing more confident I think

 

[refcast]

A bit of help is yeah harder synths like a diamond resin, or a shapton 500, at the low grit work well, or washing away loose grit for something like a cerax 320

 

[KenjiF]

Doesn’t hurt - shapton glass or other very hard synthetics will also work. Keeping things crispy has been my biggest focus these days and I’m growing more confident I think
View attachment 257116

That is crispy…

 

[noj]

A question. How do you and other polishers wind up with such a clean line between the cladding and the kurouchi? I can't imagine having that kind of control over a surface that's face down on a stone, and yet you must have followed your whole progression right up to that clean line.

I can tell you one way to make things bad .. -) Start with a stone that isn't course enough (and/or hard) and spend 12 hours grinding, not knowing any better, and making zero mistakes!

 

[noj]

Before I start on the burnishing (on the 3k) I promised, I have a question.

Whenever I progress to a finer stone in a progression on synthetics, I get a lot of black swarf that does not rinse off the stone. Unless I clean the stone with Atoma (or similar), the stone is inclined to leave dark cladding vs polish. More generally, is this effect good/bad/what you want if trying to if (I don't know what)?

Back to the question about burnishing to show the high spots, should I just keep the stone flat and mud free, and watch the effect on the blade, or do I also concern myself about the black buildup/clogging? If the latter, is is good/bad/don't-care?