Apex Bevel Geometry cross-sectional

[mrdeus]

This thread is very interesting. I tried the "fold the wire edge to one side and cut it off with an edge leading stroke" the other day when I did some sharpening and it seemed to work very well.

 

[BluntCut MetalWorks]

I spent considerable amount of time on the physics & visualization of sharpening grind interaction -> I gave up (more like deferred) for now, since who the heck want to read this dissertation anyway (ok, maybe a few of ya).

Alright then, booted myself back to Keep-Simple principle.

Sharpening stroke direction - edge trailing or edge leading or combination? I found a while back (re-invented the wheel - only sharpmaker is the purist) that edge leading stroke worked better than trailing/stropping stroke. Here is an easy experiment you can easily replicate.

Setup

Used DMT 6EF to de-burred: Used light pressure strop strokes for edge-trailing sample. Used light pressure edge-leading strokes for edge-leading sample.

Results

I don't have a SEM & SW (to construct field depth) to give a good edge/apex facing view. Just to show that 'Edge-leading 90* deburred' edge is clean and thinner than 'Edge-trailing'. I am not going to blah about variables this & that at play.

 

[BluntCut MetalWorks]

If you are not comfortable with freehand sharpening. I built a VertiSharp, a guided sharpening rig. Keep the blade vertical and use edge-leading pull-stroke similar Spyderco Sharpmaker. Now, go make your own. Note: please ignore the zip-tie.

$10 Components: a 2x2 discarded coffee table leg, a 8" hinge, a wood clamp. The wood clamp helps keep the rig more stable, especially to prevent side-tipping.

15 degrees per side setup - do one time label dps for each notch. pictured: VS + DMT 8EF + magnetic protractor

 

[mrdeus]

Interesting. Was there any difference when sharpening with the edge at 30* vs. 90* in relation to the side of the stone? I typically sharpen with the blade at an angle on water stones (like Murray Carter does in Blade Sharpening Fundamentals -- edge towards me, but diagonally across the stone). On sandpaper and on strops I usually go around 90*.

 

[HeavyHanded]

I spent considerable amount of time on the physics & visualization of sharpening grind interaction -> I gave up (more like deferred) for now, since who the heck want to read this dissertation anyway (ok, maybe a few of ya).

Alright then, booted myself back to Keep-Simple principle.

Sharpening stroke direction - edge trailing or edge leading or combination? I found a while back (re-invented the wheel - only sharpmaker is the purist) that edge leading stroke worked better than trailing/stropping stroke. Here is an easy experiment you can easily replicate.

Setup

Used DMT 6EF to de-burred: Used light pressure strop strokes for edge-trailing sample. Used light pressure edge-leading strokes for edge-leading sample.

On a fixed abrasive edge leading works better for burr removal. As one delves into fixed abrasive on a flexible or somewhat conforming backing the results begin to change ultimately burr removal/apex refinement leans toward edge trailing on a loose or partially fixed abrasive (lapping film, loaded strop, polishing grade waterstone, thin abrasive slurry on wood/glass/metal). This is why Murray Carter among others advocates for edge trailing to finish, however else one arrives at a clean grind (burr free or 90% so). Only real deviation from this is if desired grind needs to be toothier yet somewhat less finished for particular cutting qualities. Possible to completely remove burr on waterstone using leading and trailing back and forth, I believe due to mild lapping effect of loose abrasive (same as stropping on hard backing - stropping with abrasive on conformable backing allows abrasive to deflect into the backing). Instead of creating a gouge as it clears the edge plain it can roll or slide against its backing (or sink into backing if conformable) and thereby leaves a much shallower grind trough and less or no unsupported metal burring. Consider sharpening of microtome blades done with varying grades of AlumOx slurry on borosilicate platter (used to be a copper platter if memory serves) run edge trailing.

 

[BluntCut MetalWorks]

Interesting. Was there any difference when sharpening with the edge at 30* vs. 90* in relation to the side of the stone? I typically sharpen with the blade at an angle on water stones (like Murray Carter does in Blade Sharpening Fundamentals -- edge towards me, but diagonally across the stone). On sandpaper and on strops I usually go around 90*.

Yes, 30* is more refine than 90* but the burr & apex has the same effect - I didn't want to complicate the picture. I typically sharpen at around 15 to 20 degress relative to the stone. I use back & forth step all the way close to the commercially avail finishing stone and always deburr using edge-leading strokes. For super-fine edge, I use edge-leading (laterally 20*) into my diamond/cbn/Cr2O4/Alox (3microns down to 0.1micron) partially embeded stones/surfaces, thus avoided burr & wire altogether. Sometime I don't even strop on bare leather because I felt that the crazy edge go away to 1 notch below too quickly, which I suspect an nano-wire may have formed by stropping.

 

[BluntCut MetalWorks]

On a fixed abrasive edge leading works better for burr removal. As one delves into fixed abrasive on a flexible or somewhat conforming backing the results begin to change ultimately burr removal/apex refinement leans toward edge trailing on a loose or partially fixed abrasive (lapping film, loaded strop, polishing grade waterstone, thin abrasive slurry on wood/glass/metal). This is why Murray Carter among others advocates for edge trailing to finish, however else one arrives at a clean grind (burr free or 90% so). Only real deviation from this is if desired grind needs to be toothier yet somewhat less finished for particular cutting qualities. Possible to completely remove burr on waterstone using leading and trailing back and forth, I believe due to mild lapping effect of loose abrasive (same as stropping on hard backing - stropping with abrasive on conformable backing allows abrasive to deflect into the backing). Instead of creating a gouge as it clears the edge plain it can roll or slide against its backing (or sink into backing if conformable) and thereby leaves a much shallower grind trough and less or no unsupported metal burring. Consider sharpening of microtome blades done with varying grades of AlumOx slurry on borosilicate platter (used to be a copper platter if memory serves) run edge trailing.

:thumbup: see! how thing get complicated quickly even in absence of math & physics. I like your visuallization of grinding interaction. It's hard for me to render this interaction without big budget equipments but simply hand-wave that - IIA (impact incident angle, abrasive -> blade or blade -> abrasive) will shape to apex according the pressure & abrasive shape.

IIA from edge-trailing, the resultant force near apex is destructive because it's putting too much pressure to the apex and there no metal behind it to support to the deflection or tearing.

IIA from edge-leading, the resultant force near apex is constructive because pressure apply into the bevel, with more metal behind it to deter deflection or tearing. Any other collisions could dent/work-harden/dull/plastic-flow/burnish the apex but not going to form burr/wire.

edit: I experimented alot using abrasives in various state:
* fixed (diamond plate, ceramic).
* embeded (waterstone, naturalstone) - with&without mud.
* loose ~ edge-lead lapping.

My conjecture is that if the surface is flat and with embeded and or partially embeded abrasive, use edge-leading stroke will create cleaner & stronger & sharper edge.

 

[HeavyHanded]

:thumbup: see! how thing get complicated quickly even in absence of math & physics. I like your visuallization of grinding interaction. It's hard for me to render this interaction without big budget equipments but simply hand-wave that - IIA (impact incident angle, abrasive -> blade or blade -> abrasive) will shape to apex according the pressure & abrasive shape.

IIA from edge-trailing, the resultant force near apex is destructive because it's putting too much pressure to the apex and there no metal behind it to support to the deflection or tearing.

True enough, from looking at many waterstone and hard surface stropped edges there appears to be a concentration on pressure at the apex that does lead to some "tear out" at the apex - reason why waterstones without stropping produce such tremendous microtoothy edges on an extremely fine scale - also stropping on hard surface does similar, yet both are very dependednt on amount of fluid in the slurry - higher levels of vehicle to abrasive lead to less and less tear out ultimately finding its peak in the backhoning of microtome blades with thin slurry of alumox on borosilicate - presumably with no destructive qualities.

IIA from edge-leading, the resultant force near apex is constructive because pressure apply into the bevel, with more metal behind it to deter deflection or tearing. Any other collisions could dent/work-harden/dull but not going to form burr/wire.

Also appears to be a limit in grit size beyond which even straight razor users have documented edge improvement/refinement by finish stropping of a Shapton 15k or similar. Entirely possible that, should pressure not be greater then steel can support, there is little difference on fixed abrasive except that edge leading is rolling some burr/unsupported metal under the edge plain and off as speculated by Verhoeven, and edge trailing is leaving more metal attached to apex. Big question - if width of burr connection point is under target micron level (say.5 micron for example) does it even matter if any burr remains regardless of leading or trailing?

Normally I agree with edge leading and burr formation, but have also experienced very good burr removal from edge trailing, but not on hard fixed abrasive (bench stone, diamond stone etc). Should be noted again - most (all) industrial post grinding is edge trailing with very good results.

 

[BluntCut MetalWorks]

Also appears to be a limit in grit size beyond which even straight razor users have documented edge improvement/refinement by finish stropping of a Shapton 15k or similar. Entirely possible that, should pressure not be greater then steel can support, there is little difference on fixed abrasive except that edge leading is rolling some burr/unsupported metal under the edge plain and off as speculated by Verhoeven, and edge trailing is leaving more metal attached to apex. Big question - if width of burr connection point is under target micron level (say.5 micron for example) does it even matter if any burr remains regardless of leading or trailing?

Yes, it does matter because a 0.5um(or smaller) burr/wire on the edge can diagnose as:
1. grain fracture may exists = weak edge.
2. lead to roll/fold = dull edge (or toothy dull)
3. lead to tear because some of these burr/wire probably strongly pivot/hinge on a steel or carbide grain.
# maybe ok for straight razor, as long as wire/burr stronger than hairs.

Normally I agree with edge leading and burr formation, but have also experienced very good burr removal from edge trailing, but not on hard fixed abrasive (bench stone, diamond stone etc). Should be noted again - most (all) industrial post grinding is edge trailing with very good results.

:thumbup: use what work for you - I'm with you.

Industrial/microtome post grinding/Murray Carter/etc.. worked well on hard fine-grain(sub micron), low toughness steels. I've my doubt when apply trailing strokes to high alloy, high toughness and not so-fine-grain steels.

 

[Bill Hoffman]

My head hurts!

 

[BluntCut MetalWorks]

FWIW - Here is a low resolution (+ no light) pic of my current straight edge razor - DragonFly2 Zdp. Just not enough resolution & light manipulation to show how fine the edge actually is.

 

[HeavyHanded]

FWIW - Here is a low resolution (+ no light) pic of my current straight edge razor - DragonFly2 Zdp. Just not enough resolution & light manipulation to show how fine the edge actually is.

Here are a few that I found very revealing - first is 1095 carbon on a 1200 grit King - backhoned with a fairly thick mud - 1600x (1000x plus digital blow-up). Scale at upper L is 3u. Tree-topping sharp.

This one is also 1095 on a Spyderco EF followed by flexcut gold (.5 micron to 1 micron estimate) followed by plain leather - could just pass a HHT. This one at 640x - scale at upper L is 7u.

And these two as a pair because I was quite surprised at how much wasn't visible at 640x - the first image is 640, second is 1600. I expected the grind pattern to extend to the apex. This was Aus8 (I think) done on an Ace hardware AlumOx stone, stropped with white compound from Sears (maybe 1-3u?). Edge could treetop hair but just shy of whittling.

There's an awful lot to this - I stopped taking pictures/studying micrographs as I felt my sanity slipping. Now I frequently don't even use my loupe, just good lighting and a few quick cut tests. BTW the burr fold over technique as you describe is a staple of mine - I keep a short length of oak dowel in my bag for just such a purpose.

 

[BluntCut MetalWorks]

:thumbup: excellent pics Heavyhanded.

I saw these pictures of yours in 'steeling..' thread (IIRC) before but didn't registered that there are shadows next to the apex of those 1600x pics. Those look like trough/hollow lines, could imply that those edges are sharp but weak - could be interpret that those edges have sub-micron burr/wire. Hollow lines reflect/scatter light away from the receiver - therefore render as shadow, that why I speculate those edges are weak.

Your thoughts?

Edge-leading interaction is more harsh (larger impact force) than edge-trailing. So, in order to have an equivalent thiness/refine edge as edge-trailing, for edge-leading you need to use smaller abrasive in good strong binder that can resist & withstand cut/gash.

A clean thin un-compromising-geometry apex plays important role in a knife performance. It would be great if you or someone would tests & snap a few 1000x+ pics of finished edges using stroke direction.

 

[HeavyHanded]

:thumbup: excellent pics Heavyhanded.

I saw these pictures of yours in 'steeling..' thread (IIRC) before but didn't registered that there are shadows next to the apex of those 1600x pics. Those look like trough/hollow lines, could imply that those edges are sharp but weak - could be interpret that those edges have sub-micron burr/wire. Hollow lines reflect/scatter light away from the receiver - therefore render as shadow, that why I speculate those edges are weak.

Your thoughts?

I chalked it up to an effect from the cedar oil and my inability to master the lighting properly at that magnification. I notice the effect you observe on many blades I micrographed at 1600x, including factory honed razors and those done by other individuals - sometimes visible, sometimes appear/disappear simply by breaking contact with the oil and re-immersing. To get the images as I have I had to run a piece of tape off the back plane of the blade to support the oil drop necessary to focus - the oil is held in a shallow trough instead of being supported on a flat plane with the imaged bevel side. What effect this has on the way light passes thru the oil I can only speculate. I did go back and do the backdrag test as you described - in fact the backdrag test has been part of my SOP for some time. Here are a few others that are "cleaner" but I chalk the difference up to luck when preparing the tape and oil. This one is off an India stone and stropped on AlumOx compound on leather:

This one from the coarse side of an India stone and stropped on black emery compound

At 640x even if there is a burr, it's generally fragmented along the grind troughs, not continuous (tho appears continuous at 160x or lower). At this point I shrug and reduce the number of images I bother to take at 1000x or greater - instead focus on edge retention as relates to specific cutting characteristics (all informal of course).

As for how weak they might be I can only compare my own to factory edges, edges I have prep'd with various media, and anecdotal edge retention from other members. From what I understand of these, my edges are comparable and (IMHO of course) better than some other results that have been posted with comparable steels. From what I have observed (mostly at 640x but a handful at 1600) presence of submicron burrs or wire edges cannot be detected visually without SEM - optical magnification becomes too variable for untrained folk such as myself. As I said, I stopped pondering many of the variables you have mentioned in this thread as being too dependent on the material to be cut and the expected longevity of the edge, and only include my observations re burr removal and thoughts on how it relates edge leading and edge trailing. If a burr cannot be made to show itself after a backdrag test then it like as not doesn't exist or will have no bearing on performance. Consider the human eye can see the light from a cigarette at 1 mile yet cannot even begin to see the cigarette. From what I have observed, if strong light does not reflect back from a burr/wire edge at 6 or 8x (or even with the naked eye) so as to be seen, it won't be detected optically at any magnification. Of course all results wide open to interpretation.

 

[BluntCut MetalWorks]

Thank HeavyHanded:thumbup:

Your assessments are right on and I agree, edges from these 2 new pics are clean, so extrapolate back to other pics must be oil obscured light then.

Note that these nice edges were produced by you - a sharpening expert. Can a novice produce such clean edges with stropping?

If you don't mind and time permits, please post similar pics for:

1) the same blade (1095 fine-grain?) after stropped on india stone.

2) the same blade after edge-leading finished on india stone.

3) another blade with high-alloy steel such as s**v/m4 or vg-10/d2/cpm154, trailing vs leading ended on india stone.


Weak edges can be sub-micron thin or 20 microns thick or perfect but too thin below the apex. Depend on edge purpose/task, roll could instantly destroy its performance.

Later on, I like to examine how 'too thin below the apex' would affect performance for various steels - Leverage data from Ankerson's steel-ranking tests maybe we can shed some light.

 

[HeavyHanded]

Thank HeavyHanded:thumbup:

Your assessments are right on and I agree, edges from these 2 new pics are clean, so extrapolate back to other pics must be oil obscured light then.

Note that these nice edges were produced by you - a sharpening expert. Can a novice produce such clean edges with stropping?

You are too kind by half! - I almost spewed my coffee at this as I consider myself to be just a few steps up from a talented hack.

If you don't mind and time permits, please post similar pics for:

1) the same blade (1095 fine-grain?) after stropped on india stone.

2) the same blade after edge-leading finished on india stone.

3) another blade with high-alloy steel such as s**v/m4 or vg-10/d2/cpm154, trailing vs leading ended on india stone.


Weak edges can be sub-micron thin or 20 microns thick or perfect but too thin below the apex. Depend on edge purpose/task, roll could instantly destroy its performance.

Later on, I like to examine how 'too thin below the apex' would affect performance for various steels - Leverage data from Ankerson's steel-ranking tests maybe we can shed some light.

1)
Stropping on an India stone would (IMO) no doubt lead to to some sort of edge damage/burring. I almost guarantee it - possibly with an extremely light touch and some oil it could be polished so but VERY challenging.

2)
Edge leading could be done to produce a clean edge but would be relatively time consuming without a loaded strop.

3) somewhere I have 154cm (not cpm) micrographs but may have been deleted by now. Not much time for experiments of this detail lately but will keep in mind.

This is a discussion related but not exactly to our convo. The quality of some images is exceptional as is the commentary. Starts about 1/3 down the page with reference to Murray Carter straight razor honing technique.

http://jendeindustries.wordpress.com/category/straight-razor/

 

[BluntCut MetalWorks]

You are too kind by half! - I almost spewed my coffee at this as I consider myself to be just a few steps up from a talented hack.

2x humble aren't you

1)
Stropping on an India stone would (IMO) no doubt lead to to some sort of edge damage/burring. I almost guarantee it - possibly with an extremely light touch and some oil it could be polished so but VERY challenging.

2)
Edge leading could be done to produce a clean edge but would be relatively time consuming without a loaded strop.

Please finish/end normally as a regular sharpening without special/expert treatment, so we can see the effect of edge-trailing/leading on the edge at this grit.

3) somewhere I have 154cm (not cpm) micrographs but may have been deleted by now. Not much time for experiments of this detail lately but will keep in mind.

Same intention as 1) & 2) but with a higher alloy & larger grain steel.

This is a discussion related but not exactly to our convo. The quality of some images is exceptional as is the commentary. Starts about 1/3 down the page with reference to Murray Carter straight razor honing technique.

http://jendeindustries.wordpress.com/category/straight-razor/

I re-read that, yeah I afraid that not everything is a nail, even though MC is holding a hammer

 

[HeavyHanded]

I re-read that, yeah I afraid that not everything is a nail, even though MC is holding a hammer

Here is a progression I thought you might be interested in from a test I ran a number of months ago - don't believe I posted it anywhere on the forum. Again not quite part of the conversation but not far off either.

All images at 640x.
First pic (CSV_1) is of an Aus8 blade after being ground on a fine Crystalon (Norton silicon carbide) stone, and stropped on two layers of newspaper treated with the swarf and oil from the stone to deburr. In my opinion this produces the cleanest representation of the stone-ground edge (burr-wise) without substantially changing the grind pattern. The paper was wrapped around the fine side of the stone. Second pic (CSV_2) shows the effects of 40 passes/side, very light pressure on two layers of newspaper wrapped around the fine side of the stone, treated with the Sears white AlumOx compound. Third shows the effect of an additional 25 passes on a single layer of paper wrapped around the coarse side of the stone. Enough pressure was used that I could just feel the stone's texture under the paper - maybe twice the pressure I would normally use and enough that I would be concerned about rounding the edge if I were on a leather strop. I've run similar tests before, but never starting with an edge prep'd at such a coarse level to start. I was quite surprised at the transformation. The process did not raise a burr despite the amount of material removed - resulting edge could just whittle a hair. I believe there is something very different about the pressure spiking associated with stropping on an irregular backing that produces such a difference in abrasive action, but am at a loss to explain it.

 

[BluntCut MetalWorks]

...associated with stropping on an irregular backing that produces such a difference in abrasive action, but am at a loss to explain it.

Cool pics & awesome technique!

I've been working on a simple physics model of abrading interaction - dragging along with my head-cold. It's much easier to explain this case/scenario using the model - '..I have found a truly wonderful proof, but the margin is too small to contain it.' || 'A pointy-sharpened hex bolt is an interesting nail'.

edit: It's the conical bumps in the abrasive surface, changed the resultant abrading force vector less upward, more parrallel to spine-apex line.

 

[HeavyHanded]

Cool pics & awesome technique!

I've been working on a simple physics model of abrading interaction - dragging along with my head-cold. It's much easier to explain this case/scenario using the model - '..I have found a truly wonderful proof, but the margin is too small to contain it.' || 'A pointy-sharpened hex bolt is an interesting nail'.

edit: It's the conical bumps in the abrasive surface, changed the resultant abrading force vector less upward, more parrallel to spine-apex line.

My speculation is that it increases the upward force of the abrasive but in a more narrow plane - where the abrasive had it been packed shoulder to shoulder on a level field might have spiked the pressure at the apex and rounded it over, instead the blade is supported on a bed of nails so to speak. Each one exerting more pressure individually but incapable of rounding the edge over (at similar pressure overall) due to support from the other points and the sharper let-off of pressure as the edge passes over the low spots. Or something like that....We might be saying the same thing...