xavierdoc wrote:The point I was trying to get across was that the "chipped" edge of the thinned, used blade is still smoother in appearance than the unused factory edge.
Yes, this is true but it often leads people to the misleading conclusion that polished edges wear to coarse edges which of course doesn't happen. The chips that come out of a polished edges do not have the aggression as the cut tracks left by a coarse abrasive. Ironically, a coarse abrasive also will tend to wear and become smooth, but again it doesn't have the cutting ability of a polished edge though they may look similar under magnification.
Extremely nice pictures, how exactly did you take them?
Cliff Stamp wrote:The chips that come out of a polished edges do not have the aggression as the cut tracks left by a coarse abrasive.
It would be nice if a steel could be designed such that as carbides tore out or metal wore away, that a micro-serrated edge was maintained. Obviously such an edge would gradually get wider as wear progressed into the bevel. I know various manufacturers have experimented with blades with a very hard layer/coating on one side only, purporting to "stay sharp forever" as the softer, supporting metal wore, leaving the cutting edge of the harder material. I'm pretty sure it has never been convincingly achieved.
Cliff Stamp wrote:Extremely nice pictures, how exactly did you take them?
I don't have a dedicated macro lighting set-up, although I do have a macro lens for my Canon 7D. The pics are taken in natural light with a reflector. If necessary I supplement with bounced flash. Unfortunately, there is no repeatability with this method. If I were more serious about it I'd remove natural light from the equation and have a controlled, repeatable set up.
Macro photography isn't otherwise an interest of mine -I originally bought the macro lens because it filled the role of a good quality, portrait prime lens.
My interest was piqued by this article by ChrisR (member here but article at Britishblades) about an inexpensive photo-stacking set up. Gives huge depth-of-field at relatively high magnification.
xavierdoc wrote:
Macro photography isn't otherwise an interest of mine -I originally bought the macro lens because it filled the role of a good quality, portrait prime lens.
Same reason I got my Macro lens for my D90, they make excellent general use lenses because the quality is very high. :)
As suggested in my original post, I put a 30deg microbevel on the PM2. The knife has been used for lots of cutting since, in particular I carved some ebony and a spoon from spalted hawthorn (I think?):
Unused edge after microbevel:
After Ebony carving:
After spoon carving:
Clearly there has been some edge damage but the knife still cuts well and feels sharp. This was a serious work out for the knife and for me as I didn't rough out the spoon shape with an axe or saw (apart from splitting the round in half.)
After protracted carving (3+ hours) the handle was feeling pretty uncomfortable but no actual blisters and no cuts. Pretty good for a slimline folder.
I might try a 40 deg microbevel next, just to see how it influences cutting performance.
M390 (in Spyderco's hands) is turning into one of my favourite stainless steels.
Great pictures and pertinent/objective testing Xavier.
I've chipped out a 3v full tang camping knife before by going too far edge-wise (25deg inclusive) and batoning like crazy with it, I considered it part of learning.
Here's your quote ... " It would be nice if a steel could be designed such that as carbides tore out or metal wore away, that a micro-serrated edge was maintained. Obviously such an edge would gradually get wider as wear progressed into the bevel. I know various manufacturers have experimented with blades with a very hard layer/coating on one side only, purporting to "stay sharp forever" as the softer, supporting metal wore, leaving the cutting edge of the harder material. I'm pretty sure it has never been convincingly achieved." ... end of Quote
David Boye did a lot of reasearch into Dendritic Cobalt and it's crystaline-like structure that had more of a toothy edge as it wore down. Unfortunately the only David Boye knife Dendritic Cobalt that I own has a Dragon etching too close to the edge for me to sharpen , and post any actual findings, without loosing a dragon foot ... lol ... safe queen.
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I believe everybody has to find their own balance with, type of steel/heat treat/type of use/type of edge, and it boils down to different types for different folks ... you never know exactly how far you can go with an edge 'til you go too far.
I think you're spot on with your pocket knife edges on powder steels ... Good Job!
I haven't read every post so if I'm repeating someone please forgive.
My opinion is that no matter how low you go with a back bevel, especially if it is really low (<24 deg. incl.) you should use a small edge bevel. I don't mean a micro-bevel (very very small). I mean an edge bevel that is easily seen but not much bigger than that. The edge will be more durable and I doubt if a small edge bevel of 40 degrees (MAX) would hinder cutting performance. I'm speaking of an EDC or hard use knife. Of course if you are only cutting soft materials I don't think you need to worry about an edge bevel for durability. Still, over time a kitchen knife for exampleof mine would have an edge bevel due to touch ups at a higher angle than the origin bevel or back bevel.
My point is a small edge angle of 34-40 degrees inclusive won't hinder cutting in almost any situation. It will increase durability though. That's my opinion but there are a lot of cutting situations I haven't been in so take my opinion with a grain of salt.
xavierdoc wrote:It would be nice if a steel could be designed such that as carbides tore out or metal wore away, that a micro-serrated edge was maintained. Obviously such an edge would gradually get wider as wear progressed into the bevel. I know various manufacturers have experimented with blades with a very hard layer/coating on one side only, purporting to "stay sharp forever" as the softer, supporting metal wore, leaving the cutting edge of the harder material. I'm pretty sure it has never been convincingly achieved.
The problem is that sharpness is generally achieved when an edge is about half a micron in thickness, carbides, even the very small ones in PM steels, are still on the order of several microns so when they tear out they leave holes which are thicker by several times than what a sharp edge could be, thus the jagged holes left by carbide tear out leave an edge which has a sharpness only a small fraction of optimal. This is one of the reasons why the very high carbide steels can keep cutting at a fairly low sharpness for a long time. In fact you can even get spikes in sharpness where the sharpness will rise slightly after a long series of cutting where the edge gets jagged in that way.
The problem with coatings such as noted on the Buck IonFusion blades was that while it works in theory as the edge wears while the coating wears much less, and in fact it even shows up on CATRA tests giving superior edge retention. The problem is that in real use with people as the edge wears away from the very hard coating then this coating just cracks off because people can not hold a knife as steady as a CATRA machine and thus the small lateral loads from little side movements over load the coating's strength.
