Buzzbait :
There is really only one way in which steels can influence a difference in the cutting ability and this is by effecting how "sharp" they can get. In regards to slicing, while it is true for example that D2 at a very high polish will out slice 52100 at a high polish because the grain structure of D2 is much more coarse than 52100 (30-50 microns as compared to 0.5-1 micron), both slice very poorly at a high finish, so it is a matter of one being "less bad" than the other. If you sharpen both at a decently coarse finish like 600 grit DMT so that both slice well, you will see no difference in slicing ability between the two as the level of micro-teeth left by the DMT abrasive is much larger than the grain of either of the steels so the grain size is totally masked. The opposite is true for push cuts. At a high polish, 52100 will take a finer finish than D2 because of its smaller grain size, however in order to actually detect this you have to sharpen at an angle which forces the more coarse grain steel to break apart at the edge. Typically from what I have seen this means you must go below ~10 degrees per side, which is far below most modern cutlery.
2. On this same note, the choice of steel would not be noticed until a number of cuts have been made? Prolonged use is where the hardness, edge retention, and abrasion resistance start to shine through?
Yes, the steel type can effect edge retention and thus reduce the cutting ability, however the initial performance will be identical, regardless of the steel, except for the cases given in the above. To clarify the above, in order to actually see the difference I mentioned, I had to do some really controlled cutting where I could see performance changes on the order of less than 5% . It is very difficult to notice these things by "feel", unless you spend a lot of time doing it. This again is why I don't thing steel type should be linked to cutting ability as even when you can see differences, they are very small. Steel type should be chosen for reasons of edge retention, overall durability, corrosion resistance etc. . Which brings up another point. In the above I assumed that the geometry was the same for the D2 and 52100 blade, in general this should not be true as 52100 is much tougher and thus should be able to make a higher performance cutting blade, except on light work where even the durability of D2 will not be exceeded.
3. As for convex and puukko style grinds, I?m not seeing the downside. Comparatively few knives are made with these types of grinds. Why is the knife world dominated by your average hollow grind and two distinct edge bevels? Is it that hard to convex or puukko grind most steels? Or is it just too hard to polish most steels?
The most common using knives (blades) have full grinds, such as puukkos, parangs, khukuris, axes etc. . They have only one drawback and this is that when you are sharpening you must work the entire bevel. However they have the advantage that if you do so, the cutting ability is constant as the geometry of the edge stays the same. This doesn't happen with knives with secondary bevels because each time you sharpen them the cutting ability goes down as the edge thickens. This change happens faster for convex than flat than hollow primary grinds with secondary edge bevels.
phlatinum :
Looking at it from the flip side, does the hollow ground blade offer any advantages over the flat or convex ground blade from the user's standpoint (in a utility knife, or hunting knife, for that matter)??
There are two ways to hollow grind a blade. The following shows flat, traditional hollow, convex and hollow relief :
http://www.physics.mun.ca/~sstamp/images/grinds.xfig.gif
The problem with the traditional hollow is that the curvature near the top is quite extreme and the blade binds badly on deep cuts. The primary advantage over a flat grind is that since you have more metal removed from the upper part of the blade you can go with a thicker edge and have the same level of cutting ability and thus have a more durable edge under light impacts. However the downside is that if the durability of the edge is exceeded you can blow a piece out of the primary grind and thus basically write off the knife. The other advantage is as db mentioned, this grind is the more stable than flat or convex (with secondary edge bevels) under repeated sharpenings.
The hollow relief grind (found on axes, khukuris, etc.) is basically a hollow grind on top of a flat or convex primary grind. Unlike the traditional hollow, the hollow relief enters and exits the blade at a very similar angle, and thus it has has no problem with binding on deep cuts and in fact will greatly increase deep penetration. It also has the huge benefit of directly increasing the ease of sharpening. You still sharpen the entire bevel, just that now the middle has been removed and thus there is far less metal to grind. If you thought stropping a full grind was easy, try a hollow relief.
The downside to both types of hollow grinds is of course the extreme fragility in case of impacts, and the much lower strength than flat or convex grinds, neither are of any important for small cutting knives.
Posted by phlatinum :
Would it be accurate to say that the flat/convex ground blade has a longer total life expectancy than an otherwise similar hollow ground blade, or vice versa?
Flat or convex full ground blades with no secondary edge bevels will last much longer than hollow ground blades with secondary edge bevels. What tends to happen with full ground blades (no secondary edge bevels) is that as they are thinned with repeated sharpenings, they get used for lighter work. For example a wood chopping parang that is flat ground and starts out at 1/4" thick and 2" wide may after many years be cut down so it is only 1/8" thick and 1" wide, it now is devoted to a light grass/brush cutter. On the flip side, if it had a secondary edge bevel, after the same amount of sharpening, it would still be 1/4" across the spine however the edge would be so thick that it would have long past the point of being useful as a cutting tool and would be used instead as a root / sod hacker.
Buzzbait :
.... the thickness of the blade is a big deal, with it becoming less and less of an issue as you move away from the working edge.
Exactly, as when cutting materials the force they exert on the blade (binding), falls away very rapidly as you move away from the edge.
The big issue, at least for me, is whether to bevel a blade?s edge or let the edge run smooth to the tip of the knife.
There are a few reasons for the introduction of secondary bevels. First off knives are not really cutting tools anymore. As an example look at any well known "tactical" knife, it will easily be out cut by one of the larger Swiss Army knives. When you want to use a knife for digging in the dirt, chopping bone, coming into contact with hardened metal etc., you have to alter the profile away from one of optimal cutting ability. To make matters worse, the cutlery industry is flooded with steels that are really unsuitable for the knives they are being used on, because of their extremely brittle nature (ATS-34 as compared to say L6), and thus the geometry of the edge has to be made even more obtuse. Third, the introduction of gadgets like the Sharpmaker, which are designed for secondary bevels. Which came first is not trivial, but the flood of such products certainly makes using full grinds not that practical if you are a maker. Lastly, fully ground blades look horrible after they are sharpened as you are abrading the entire bevel, this is not a practical geometry for the huge part of the market which is influenced by the look of the primary grind (coatings, various decorative finishes).
However, if you just want to use your knife as a pure cutting tool, and you don't care that the bevel gets scratched up none of the above applies to you and thus go with a full grind, optimally with a hollow relief. Edges can be ground right down to 10 degrees for about any steel and ~6-8 degrees for the finer grained ones. These edges will not be damaged when slicing wood, rope, cardboard, etc.. For wood chopping you don't even have to go that much more obtuse assuming you are working on clear soft woods, with good technique. If you are chopping knots you want a thicker bevel, ~12-14 degrees, more if the technique is poor, or the wood very hard. The reason that people recommend angles like ~25+ degrees per side for simple wood chopping is simply becuase the steels being used in the blades are not suitable and thus you are having to compensate for a lack of toughness. Bone chopping requires a more obtuse edge again, but this is now starting to now really be a cutting knife anymore.
There are two very basic techniques for sharpening full grinds :
The first is to simply hone the full bevel producing an angle that is constant form spine to edge. This is how puukkos are sharpened, usually at 8-10 degrees. The second method is for blades with primary grinds that are much more acute. If your primary grind is flat at 2-4 degrees, the edge formed by this angle will be rather weak. Thus as you are stropping, you roll the blade upwards just on the last of the stroke. This creates a very minute secondary edge bevel, left usually at just a few degrees above the primary. This increases the strength greatly and only loses just a little bit of cutting ability. Note each time you sharpen you are still working the whole bevel, you can do touch ups on the micro-bevel to save yourself some time, which is common practice. Convex bevels are handled in the same manner, you just arc the hone over the bevel if you are using a stone, or use a slack piece of sandpaper (or one on a really soft backing), if you are using a stropping motion.
-Cliff
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