Bevels

[Khaki]

I'm new to the knife sharpening and blade steel type game and have been reading up what I could find on this forum.
I've seen lots of stuff about secondary (or micro) bevels and figures of 15 deg to 20 deg per side.
There's also been plenty of references to thinning but without not a lot of numerical info.
So I've been playing with some Japanese monosteel AUS8 knives, trying to thin them in a flat grind from about 0.5 to 1 mm behind the edge to 6 to 10 mm behind to the point where this meets the blade face (the shinogi line as I understand it).
To create this primary bevel on a fixed angle jig, I usually end up with an l of 3 to 3.5 deg, to which I then apply a 16 deg secondary which meets the primary at about 1 mm behind the edge. I end up with about 0.5mm thickness at this point.
Seems to work well enough, and looks good, but are these the sort of numbers others work to, or achieve, or even recommend/decry?
I haven't done my sine or tan calculations on this arrangement yet and probably should, but I left school 60 years ago so it might take a while.
Any input would be appreciated.

 

[aporigine]

I'm new to the knife sharpening and blade steel type game and have been reading up what I could find on this forum.
I've seen lots of stuff about secondary (or micro) bevels and figures of 15 deg to 20 deg per side.
There's also been plenty of references to thinning but without not a lot of numerical info.
So I've been playing with some Japanese monosteel AUS8 knives, trying to thin them in a flat grind from about 0.5 to 1 mm behind the edge to 6 to 10 mm behind to the point where this meets the blade face (the shinogi line as I understand it).
To create this primary bevel on a fixed angle jig, I usually end up with an l of 3 to 3.5 deg, to which I then apply a 16 deg secondary which meets the primary at about 1 mm behind the edge. I end up with about 0.5mm thickness at this point.
Seems to work well enough, and looks good, but are these the sort of numbers others work to, or achieve, or even recommend/decry?
I haven't done my sine or tan calculations on this arrangement yet and probably should, but I left school 60 years ago so it might take a while.
Any input would be appreciated.

I’d freehand in a bit of convexity. A full-flat grind, even only 1cm of it, could have a detrimental effect on food stiction.

I’d take it as close to a zero grind as you dare, then put a microbevel on that would need magnification to see. Imo those two steps will wrong max performance out of the knife.

Shinogi is when there is a definite step from blade road to the flat below the spine. Most of my knives are gently convex from edge to spine; no shinogi.

 

[azn_knives_4l]

I'm new to the knife sharpening and blade steel type game and have been reading up what I could find on this forum.
I've seen lots of stuff about secondary (or micro) bevels and figures of 15 deg to 20 deg per side.
There's also been plenty of references to thinning but without not a lot of numerical info.
So I've been playing with some Japanese monosteel AUS8 knives, trying to thin them in a flat grind from about 0.5 to 1 mm behind the edge to 6 to 10 mm behind to the point where this meets the blade face (the shinogi line as I understand it).
To create this primary bevel on a fixed angle jig, I usually end up with an l of 3 to 3.5 deg, to which I then apply a 16 deg secondary which meets the primary at about 1 mm behind the edge. I end up with about 0.5mm thickness at this point.
Seems to work well enough, and looks good, but are these the sort of numbers others work to, or achieve, or even recommend/decry?
I haven't done my sine or tan calculations on this arrangement yet and probably should, but I left school 60 years ago so it might take a while.
Any input would be appreciated.

Terms get mixed up a lot depending on who you're talking to? Some people think of lowering the edge angles and applying a micro-bevel as a kind of thinning and others restrict it to adjusting the spine to edge taper at the grind. There's variation, ofc, but a full flat ground Victorinox is something like 1° to 3° per side from the spine so, y'know... *low*, lol. A typical Japanese-style knife with a shinogi and a blade road will be something more like 2° to 5° per side from the top of the blade road so *still* very low Most consumer jigs won't be able to achieve these angles.

 

[Khaki]

Terms get mixed up a lot depending on who you're talking to? Some people think of lowering the edge angles and applying a micro-bevel as a kind of thinning and others restrict it to adjusting the spine to edge taper at the grind. There's variation, ofc, but a full flat ground Victorinox is something like 1° to 3° per side from the spine so, y'know... *low*, lol. A typical Japanese-style knife with a shinogi and a blade road will be something more like 2° to 5° per side from the top of the blade road so *still* very low Most consumer jigs won't be able to achieve these angles.

As for achieving the low angles, I made an attachment (timber and pretty primitive - I'm embarrassed to show a picture of it) to fit the stone carrier on my TS PROF so I can go as low as I like, even a few degrees negative, with the down side being I can only use about 3" of a 6" stone. Works OK though, and both accurate and repeatable.

 

[azn_knives_4l]

As for achieving the low angles, I made an attachment (timber and pretty primitive - I'm embarrassed to show a picture of it) to fit the stone carrier on my TS PROF so I can go as low as I like, even a few degrees negative, with the down side being I can only use about 3" of a 6" stone. Works OK though, and both accurate and repeatable.

View attachment 334462

Nice problem solving

 

[Nemo]

I've thinned out a couple of entry level aus8 knives. They were both pretty thick behind the edge, so it was a decent amount of work. I used a Chosera 400 the first time. The second time was several years later and I used 80 grit sandpaper in a sandpaper holder which was quite a bit easier.

I lay the knife flat on the stone then apply pressure just behind the edge as I grind. This automatically adjusts the grinding angle to match the angle of the blade just behind the edge. It's probably a few degrees but the actual angle doesn't matter. What matters is where you are removing metal. You want to remove metal just behind the edge. You can go all the way to a zero grind but you will risk changing the profile, especially with a coarse stone. I'd advise stopping when the original edge bevel is very small, (well under 1mm) but still visible.

The key thing to note is that metal will be removed from where you put pressure on the blade. If you put pressure behind the edge, metal is removed behind the edge. Pressure halfway up the blade (as in raising the shinogi on a wide bevel knife) will remove metal halfway up the blade. pressure in between these two will remove metal in between. The knife will automatically align to the correct angle when you use pressure in this way.

 

[Nemo]

I should add that if you use a jig, you will be cutting a new relief bevel which will necessarily change the geometry of the knife. If you thin the way I described, the geometry will be more similar.

 

[Nemo]

The other option is that you can start thinning by "knocking the shoulders off". I wonder whether that is what you were describing? This will provide a decent performance improvement with much less effort. Once again, the exact angle doesn't matter but I guess circa 5 degrees is a reasonable starting point.

Edited to add: This does change the geometry behind the edge a little but does not change the geometry higher up the blade.

 

[cotedupy]

Terms get mixed up a lot depending on who you're talking to

^This^

If you’re trying to read up about this kinda thing, aways remember that people use a lot of these terms in different ways. It’s annoying and confusing, but that’s just the way it is.

I've thinned out a couple of entry level aus8 knives. They were both pretty thick behind the edge, so it was a decent amount of work. I used a Chosera 400 the first time. The second time was several years later and I used 80 grit sandpaper in a sandpaper holder which was quite a bit easier.

I lay the knife flat on the stone then apply pressure just behind the edge as I grind. This automatically adjusts the grinding angle to match the angle of the blade just behind the edge. It's probably a few degrees but the actual angle doesn't matter. What matters is where you are removing metal. You want to remove metal just behind the edge. You can go all the way to a zero grind but you will risk changing the profile, especially with a coarse stone. I'd advise stopping when the original edge bevel is very small, (well under 1mm) but still visible.

The key thing to note is that metal will be removed from where you put pressure on the blade. If you put pressure behind the edge, metal is removed behind the edge. Pressure halfway up the blade (as in raising the shinogi on a wide bevel knife) will remove metal halfway up the blade. pressure in between these two will remove metal in between. The knife will automatically align to the correct angle when you use pressure in this way.

^Also this^

Which is as good a distillation of how to thin a knife well as you’ll ever read. If you follow that advice, and do it freehand (ie without a jig or guide) - you will automatically get an ideal amount of micro-convexity into a bevel that is very thin bte.