Blade Grinds, Edges and Geometry

[Alantoo]

I was always impressed with how effective the offset / chisel grind of a grafting knife was in keeping a flat plane across a stem instead of following the grain. A good pointer as to why it is fairly important for a blade edge to be symmetrical for other uses.

I would be interested to hear your take on sharpening sytems.

My furniture maker father always held that a blade edge was stronger and lasted much longer if the grinding/sharpening/honing was done at right angles to the edge. ie the abraded marks were at right angles to the edge, rather than along the edge as you get from something you draw the blade through like a Lansky system. He was referring to hand plane and chisel blades but I have always applied it to most edge tools...the main exception I can think of being sickles and scythes which I do in small circles

The basis being that when at right angles to the edge the abraded microgrooves provide a series of microscopic but strong "teeth".

When the microgrooves from whatever final grit/polish used were running along the edge they provided a weak snap off point like a bar of chocolate or loo paper.

I guess it comes down to the relationship of grain size of the metal and abrasive particle size of the the final sharpening medium used. For materials like wood with the old carbon steel blade hand tools it seems to hold true.

The burnishing effect of a butchers steel would also help in this by reducing any of the microgrooves left by abrasives or polishes?

Alan

 

[Stuart Mitchell]

I was always impressed with how effective the offset / chisel grind of a grafting knife was in keeping a flat plane across a stem instead of following the grain. A good pointer as to why it is fairly important for a blade edge to be symmetrical for other uses.

I would be interested to hear your take on sharpening sytems.

My furniture maker father always held that a blade edge was stronger and lasted much longer if the grinding/sharpening/honing was done at right angles to the edge. ie the abraded marks were at right angles to the edge, rather than along the edge as you get from something you draw the blade through like a Lansky system. He was referring to hand plane and chisel blades but I have always applied it to most edge tools...the main exception I can think of being sickles and scythes which I do in small circles

The basis being that when at right angles to the edge the abraded microgrooves provide a series of microscopic but strong "teeth".

When the microgrooves from whatever final grit/polish used were running along the edge they provided a weak snap off point like a bar of chocolate or loo paper.

I guess it comes down to the relationship of grain size of the metal and abrasive particle size of the the final sharpening medium used. For materials like wood with the old carbon steel blade hand tools it seems to hold true.

The burnishing effect of a butchers steel would also help in this by reducing any of the microgrooves left by abrasives or polishes?

Alan

All very interesting that, thank you.

Most of the edges I finish are stropped, so almost polished, that said for a working knife that requires a tough 'beater' of an edge, I tend not to strop too much, I think that a trace of a microscopic serrate is a good thing. I think I'd agree with your dad.

 

[sh1kar]

All very interesting that, thank you.

Most of the edges I finish are stropped, so almost polished, that said for a working knife that requires a tough 'beater' of an edge, I tend not to strop too much, I think that a trace of a microscopic serrate is a good thing. I think I'd agree with your dad.

Stuart. Remind me of the sharpening angle for the YDS
Thanks
S

 

[Stuart Mitchell]

Apart from the profile of the grind. Say a little about the angle of edge. 15-30 degs say. And why. Related to profile or the steel used?

Sorry for the delay with this, managed to crack a couple of ribs so been resting up a little.

Edges are very interesting things aren't they, very much A horses for courses type of thing too. In the past I spent a lot of time on knife focused fora, many members on those fora were not necessarily knife users, a lot were collectors and fondlers, they'd sit and sharpen and hone and strop, 'hair popping' edges was the goal, no sheet of paper was safe.

That is all well and good and it might be a nice feeling to sit and slice paper, but is that the edge you want if you are in a field in the pi$$ing rain with a job to do that relies on the edge of the only knife that you have on you? I am not sure it is, I think you want a good steel that bears a tough, beater of an edge as I just described it, if it can slice paper as well that is all well and good, as long as it is doing what you need to do though, and it is doing it well, I wouldn't be concerned if it doesn't.

It is no secret that I am very fond of the SF100 steel that I predominantly use, I have described it previously on here as a real world steel, it does that that edge required and holds it well, a huge bonus too is that when you need to resharpen it, because you will, you can. I do all my sharpening free hand and I aim for an angle of 18/19 degrees, for me, for that steel, that is the sweet spot.

I apply that edge by means of a stone, running under power, to gently whet the bevel into place, then again under power I have an old cotton buff that is impregnated with gawd only knows how many years of polishing compound, more years that I have been around I would wager.

 

[VSS]

I was always impressed with how effective the offset / chisel grind of a grafting knife was in keeping a flat plane across a stem instead of following the grain. A good pointer as to why it is fairly important for a blade edge to be symmetrical for other uses.

I would be interested to hear your take on sharpening sytems.

My furniture maker father always held that a blade edge was stronger and lasted much longer if the grinding/sharpening/honing was done at right angles to the edge. ie the abraded marks were at right angles to the edge, rather than along the edge as you get from something you draw the blade through like a Lansky system. He was referring to hand plane and chisel blades but I have always applied it to most edge tools...the main exception I can think of being sickles and scythes which I do in small circles

The basis being that when at right angles to the edge the abraded microgrooves provide a series of microscopic but strong "teeth".

When the microgrooves from whatever final grit/polish used were running along the edge they provided a weak snap off point like a bar of chocolate or loo paper.

I guess it comes down to the relationship of grain size of the metal and abrasive particle size of the the final sharpening medium used. For materials like wood with the old carbon steel blade hand tools it seems to hold true.

The burnishing effect of a butchers steel would also help in this by reducing any of the microgrooves left by abrasives or polishes?

Alan

That has always been my understanding, too.

 

[Stuart Mitchell]

The old cotton buff, the working surface being heavily compressed cotton originally intended as a surface that could be dressed over and over with grits for glazing (following grinding, pre-polishing), I have only ever seen it used as a powered strop though.

 

[Alantoo]

If my knives and I happen to coincide with being over at the forge I have been giving them a final whizz strop on the polishing spindle with the magic Menzerna yellow compound P175 which they rate at Cut 2 Colour 9 and I see they are now doing one with Cut 1 Colour 10, the M5, which I must get a stick of to try.

Guide to Menzerna Compounds for all metals | The Polishing Shop

guide to menzerna compounds for all metals, quick guide to menzerna metal polishing compounds more det

www.thepolishingshop.co.uk

Chalk and cheese to the old Cannings Lustre and Rouge...of which I have a box of (40 year) old stock if any body is interested!

Alan

 

[Alantoo]

Edges are very interesting things aren't they, very much A horses for courses type of thing too

I remembered reading some prepper holding forth proudly about his knife being shaving sharp and able to cut mild steel without losing its edge.

The (dearly loved) cheapo CK knife that has been in my pocket for a few decades is pretty soft and has ended up with such a narrow included angle that it is useless for cutting anything other green wood, rope, string, packaging tape or cardboard...but it does those frequently and perfectly! If I want to cut metal I use a proper tool for the job a bench shear, gas axe, hacksaw or angle grinder!



The other thing about my CK blade profile is that being concave it bites deeper as you draw it through something like rope, or a branch when whittling. I still have the straight lambsfoot blade I used to use as a lad, but the concave one is even better ergonomically in this aspect.

Any ideas why so many pocket knife blades are convex in profile which tends to make them ride out of the cut as you draw it through?

Alan

 

[fizzbangwhallop]

I was always impressed with how effective the offset / chisel grind of a grafting knife was in keeping a flat plane across a stem instead of following the grain. A good pointer as to why it is fairly important for a blade edge to be symmetrical for other uses.

I would be interested to hear your take on sharpening sytems.

My furniture maker father always held that a blade edge was stronger and lasted much longer if the grinding/sharpening/honing was done at right angles to the edge. ie the abraded marks were at right angles to the edge, rather than along the edge as you get from something you draw the blade through like a Lansky system. He was referring to hand plane and chisel blades but I have always applied it to most edge tools...the main exception I can think of being sickles and scythes which I do in small circles

The basis being that when at right angles to the edge the abraded microgrooves provide a series of microscopic but strong "teeth".

When the microgrooves from whatever final grit/polish used were running along the edge they provided a weak snap off point like a bar of chocolate or loo paper.

I guess it comes down to the relationship of grain size of the metal and abrasive particle size of the the final sharpening medium used. For materials like wood with the old carbon steel blade hand tools it seems to hold true.

The burnishing effect of a butchers steel would also help in this by reducing any of the microgrooves left by abrasives or polishes?

Alan

Good post Alan…….taking it sideways, it’s interesting that David Boye followed the same line of thought on micro-serrated edges when developing his Dendritic Cobalt alloy line of knives…

The Boye Knives Difference: Dendritic Cobalt Blades

What is Boye Dendritic Cobalt? Our unique blade metallurgy has carbide micro-teeth along the cutting edge and throughout the blade matrix. Cuts up to 100X longer than ordinary knife steel and sharpens fast. Interested? Find out more.

www.boyeknives.com

I’ve got 2 different sizes of his Boye Basic and a folder and I can vouch for the edge on these, my original Basic 3 did getting on for 20 reds one week before needing a touch up many years ago. I was impressed, as was the pro-stalker I was with…..he kept saying “scalpel” as he got down to the job in hand!

Cheers

fizz


snap on the little CK….inherited from my mum, having done the gardening it lived in her art box for sharpening pencils

 

[Stuart Mitchell]

The other thing about my CK blade profile is that being concave it bites deeper as you draw it through something like rope, or a branch when whittling. I still have the straight lambsfoot blade I used to use as a lad, but the concave one is even better ergonomically in this aspect.

Any ideas why so many pocket knife blades are convex in profile which tends to make them ride out of the cut as you draw it through?

Alan

If by concave you mean hollow, is in the diagram in the first post, I would imagine it all boils down to cost, the hollow would cost more I suspect. It is a more difficult thing to undertake.

 

[Alantoo]

If by concave you mean hollow, is in the diagram in the first post, I would imagine it all boils down to cost, the hollow would cost more I suspect. It is a more difficult thing to undertake.

No I meant in the other plane. The profile of the blade edge being concave like a pruning knife / hook, or straight as in a lamb or sheepsfoot. Not the profile of the blade cross section as in the OP Hollow grind...

My CK has become a Full Flat Grind coming to a convex edge....but its edge is concave along its length if you see what I mean!

It was the advantage of "biting in" of the concave / hooked blade rather than the tendency of "riding out" that most pocket knives have like the classic Opinels and Buck knives that I have always been curious about...

I understand the need for convex profile blade shapes for things like kitchen knives used for cutting down onto a board or for skinning and gralloching knives and etc. but pocket knives (and penknives specifically!) are for cutting points on things like sticks and quills and cutting the twine off straw bales where a straight or hook type / concave profile knife is a better shape for the purpose.

I am sure the popularity of the clip and drop point has more to do with what the buyer likes the look of rather than a knife maker's choice, whether that is blade shape or production cost...but how often does a pocket knife need to be stabbed into something relative to the number of times it needs to cut through?

Semi-tongue in cheek, but with a slight edge of genuine intrigue as it's one of my hobby horses!

Alan

 

[Alantoo]

snap on the little CK….inherited from my mum, having done the gardening it lived in her art box for sharpening pencils View attachment 263420

Honorable and perfect use for a pen(cil) knife.

Interesting. I have bought both cobalt and carbide twist drills for drilling 316 stainless steel...they were both very hard and held their edges better than HSS but even the Cobalt ones were incredibly brittle...a Ø7mm drill rolling off the bench onto a softwood floor just pinged in two.

Obviously you shouldn't use any knives as a pry bar, but are you aware of any Boye blades that have failed that way? From shock or sideways stress? I note the "They are not screwdrivers!" comment.

I also spotted a contradiction at start and stop of the leaflet that the proof reader didn't...should have changed the penultimate paragraph to read "metal" or "material" instead of "steel"...the first line clearly states "Boye Dendritic cobalt is not steel"

The sharpening instructions have echoes in the process I use for sharpening my site drilling diamond core drills. The diamonds get polished smooth if drilling something very hard like granite paviours. Even with the drill rig held down you can't exert enough pressure to push the copper matrix back to expose more diamonds...drill a few millimetres into sandstone or a soft breeze block and away you go again...in desperation I have even resorted to whacking the diamond segments with a big file to push the copper back on occasion!

Alan

 

[fizzbangwhallop]

Obviously you shouldn't use any knives as a pry bar, but are you aware of any Boye blades that have failed that way? From shock or sideways stress? I note the "They are not screwdrivers!" comment.

Not to my knowledge but then, I've never looked…… however, much to my annoyance/shame, I recently noticed that there is a slight ‘twist’ in the blade of the smaller Basic…. I can only just feel it with a fingertip but it’s more obvious as I turn the blade in the light to just show the distortion..it appears that I put a twisting force on it as it goes both ways…

You can just see the twist in the brighter section with the darker bit to its right…

Doesn't affect its cutting ability but now I know it’s there…..

 

[Alantoo]

Not to my knowledge but then, I've never looked…… however, much to my annoyance/shame, I recently noticed that there is a slight ‘twist’ in the blade of the smaller Basic…. I can only just feel it with a fingertip but it’s more obvious as I turn the blade in the light to just show the distortion..it appears that I put a twisting force on it as it goes both ways…

You can just see the twist in the brighter section with the darker bit to its right…
View attachment 263477
Doesn't affect its cutting ability but now I know it’s there…..

Do you think that has happened in use? I am interested that the blades are lost wax shell cast...I was thinking when I read the Boye web site blurb....I wonder how they manage to get such a thin piece of wax out of the rubber mould with out distorting it before they dip or spray the Porcelain layer on.

Did I understand they don't grind after casting, just tumble polish as-cast straight from the mould or did I get that wrong?

I was more concerned at the possible brittleness with that material rather than twistability...if anything I would consider your twist is good news!

Alan

 

[fizzbangwhallop]

Do you think that has happened in use? I am interested that the blades are lost wax shell cast...I was thinking when I read the Boye web site blurb....I wonder how they manage to get such a thin piece of wax out of the rubber mould with out distorting it before they dip or spray the Porcelain layer on.

Did I understand they don't grind after casting, just tumble polish as-cast straight from the mould or did I get that wrong?

I was more concerned at the possible brittleness with that material rather than twistability...if anything I would consider your twist is good news!

Alan

To be honest I don’t know…. I only noticed it last year when I spotted the reflection change in the light one day, I’m just assuming it was me at some point.

I’ve had the knife for a lot of years now… I know the bigger one came from one of the original NEC shows, which must put it back to 25years or so?

It was a lot of money then too…..both have been very nice to use and don’t get slippy (or stained) when wet or covered in blood.

cheers

fizz

 

[Alantoo]

The other interesting tool regarding "Blade Grinds, Edges and Geometry" I have used is on a draw knife which is a smaller scale version of an Adze with its rounded back enabling you to scoop out and control the depth and direction of cut. It is flat on one side and fairly steeply convex ground on the other so you have the lever advantage to rock it on the convex face close to the edge. In a similar way the blunter symmetrical convex grind of a Froe enables you to change the angle and direct the split and keep it central or wherever you want it. Flat or hollow grinds on these tools wouldn't work because it would mean you are trying to pivot the blade angle from the spine / back edge which would require much more energy....

Not very good photos but the top photo shows the convex underside and the bottom one the flat surface.





I was given this lovely old Crown Steel draw knife as a lad, you can see the linear wrought iron grain on the spine and handles and the finer grain blister steel edge clearly. A joy to use. And judging by the narrowness of the remaining blade, well used in its time. Another thing my father used to say about edge tools was that he was never worried about buying a much sharpened almost worn-out tool...it showed it had worked well! An old, but as new unworn condition tool was very suspect, uncomfortable? Ill balanced? Didn't hold its edge? Too heavy? Too light?

Alan

 

[Stuart Mitchell]

I was grinding a few FFG (Full Flat Grind) blades yesterday so thought I'd get a photo once one was roughed out, roughed to 36 grit here. I hope they show a bit of what I try to achieve with the way I grind.

The first one shows the blade edge, I tend not to get too hung on measuring and such but I am guessing at this stage around .7mm thick.

Second and third photos show the mark side and pile side of the blade respectively, both with their flat bevels from spine to edge.

The third shows the spine, a flat grind on a tapering width blade, by it's very nature, will produce a beautiful distal taper from the plunge of the grind towards the tip.

This is one of those times when I need to remind myself I am not on a knife forum, my FFG grinding went through a hefty transition a few years ago, as said it's a bit 'knifey' but if anyone would like to see how and why I have a few photos of that too.

 

[Alantoo]

Interesting new terminology for me as a non knife maker.

Do you have a view as to the origins of naming Mark and Pile side...and are they invariably the same orientation for all knives?

When discussing tapers with other blacksmiths I have often described the different form of taper we forge, and the different speed the eye travels along them...straight taper, hollow taper and convex taper. One of the classic uses of those various tapers would be in preparing the bar prior to wrapping around a scroll jig...and the scroll form itself with its tapered spiral space between the coils can also have those dynamic features.

Do you use those different distal taper forms along the length of the blade? Is there a consensus of the appropriate distal taper form for balance and intended function between knife makers or do individual makers tend towards one form for their knives? Maybe a stupid / non question....being just a function of the FFG and the blade profile.

Alan

 

[Stuart Mitchell]

Interesting new terminology for me as a non knife maker.

Do you have a view as to the origins of naming Mark and Pile side...and are they invariably the same orientation for all knives?

When discussing tapers with other blacksmiths I have often described the different form of taper we forge, and the different speed the eye travels along them...straight taper, hollow taper and convex taper. One of the classic uses of those various tapers would be in preparing the bar prior to wrapping around a scroll jig...and the scroll form itself with its tapered spiral space between the coils can also have those dynamic features.

Do you use those different taper forms along the length of the blade? Is there a consensus of the appropriate distal taper form for balance and intended function between knife makers or do individual makers tend towards one form for their knives? Maybe a stupid / non question....and just a function of the FFG and the blade profile

Alan

This is Sheffield'ish of course, but the mark side is the side that gets the blade mark, with your knife in your right hand pointing towards the sky, edge facing left, that is the the mark side, always. Pile side is obviously the other side, I am not 100% sure of the origins of the name but for me, it would be because when you mark the mark side, with a struck mark, as would have been the way, you are left with a 'pile' of metal on the other side of the blade, so the pile side?

I would imagine degrees of taper through blades and tangs are personal things from maker to maker?

 

[Stuart Mitchell]

Your question on degrees of taper now has me thinking about blade my own grinding @Alantoo

When I grind any blade I consider myself as being quite fortunate in as much as I don't rely on jigs or clamps in any way, it is all totally free hand, now I am not saying there is anything wrong with jigs/clamps, they just are not for me, each to their own.

There are a few things going through my head whilst I am grinding, steel type and thickness, obviously grind requirements, ultimate usage of the knife, handle material to be used (which can have a huge weight bearing), all that type of stuff, I consider my way fortunate because what I realise is that much of my process relies upon feel and touch, with any particular blade always in hand and that thinking in mind, I kinda try and marry all together.

Whilst grinding I tend to pace the workshop, I grind all my blade post HT so there is a lot of quenching in water involved, I tend to study the blade in between the quenching and next grinding pass, sometimes by eye but definitely not always, sometimes I will purposely not look at the blade but I'll feel it, feel it for balance but also I'll run my fingers along the bevels, feel the spine and the edge, I'll try and imagine what the weight of the finished article will be like.

There's a degree of guesswork involved of course, it goes someway to help me get my steps in though