I am writing this article for three reasons. First, to help people...

I am writing this article for three reasons. First, to help people better understand the process of sharpening. Secondly, to serve as a reference and guide for those wanting to learn to sharpen more effectively. Lastly, and possibly moreimportantly, to help people understand the concept of sharpening and the varying points to which tools can be sharpened. With this understanding people will hopefully be better able to make the best possible decisions regarding the care and maintenance of their tools.

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This is not a sharpening tutorial nor a how to, but understanding each of these concepts will help you to how to more effectively. Also, as this is not a how to I am not necessarily explaining the sharpening process per se. I am instead attempting to explain the main points of focus that should be considered before, during, and after sharpening.

This has also been written with the hope that it will cater and appeal to a broad spectrum of readers. For some of the more knowledgeable and experienced sharpeners there may be parts that may seem a bit novice and over explained, and for the less experienced I hope I have not made it too mind numbing in it's technicality. Skirting the line between the two was a huge challenge and although I know this could be explained more simply, it could definitely go the other way as well Enjoy!

Part 1

What is sharpening?

Sharpening at it's essence is a process of refinement. It is the refinement of an edge. That is, to make a blunt, rounded, damaged or otherwise ineffectual cutting edge sharp again. This refinement has two main aspects, both of equal importance finish and shape. The act of this refinement, sharpening, can happen through many different means, some rough and rugged, some delicate and precise or by a myriad of different means in between. The one thing they all have in common is that they all refine in the same way: by using an abrasive of some sort to cut and remove material to shape the tool to a point that ultimately achieves the desired end result of sharpness.

Abrasives:

It should go without saying that in order to understand sharpening one must also understand abrasives. After all, the abrasive is the tool in the sharpening process and it is of absolute necessity to understand the tool if one wishes to understand how to use it.

Pretty much any abrasive can be used to sharpen, from sand paper to Japanese ceramic sharpening stones to diamond coated honing plates, smooth stones, and even the floor of a prison cell. After all, all abrasives accomplish the same result (material removal) and are of the same basic construct (cutting agent held in place by a bonding agent). Every sharpener has his preferred type of abrasive, so finding the type of abrasive that works best for you and gives a result and finish that you are happy with is a matter of research, availability and trial and error. The main thing to learn, know and understand about abrasives is what they are and how they work.

Grit and Micron:

There are two scales in reference to the measurement of the cutting agent particles in abrasives, both based on the measurement of size.

The first and most common is grit, which works on an ascending numerical scale from low to high (low number = rough/more aggressive cutting, high number = smooth/less aggressive cutting). The particles of cutting material are sized by the number of parts in a given area (i.e. parts per square inch or centimeter). This means that the larger a particle is, the fewer will be able to fit in a given area, conversely the smaller a particle is the more of it. With this measurement scale the lower the number the rougher the abrasive (I.e. 60 grit is rougher than 100 grit).

The second and less common method of measurement is micron. A micron is the measurement of an individual cutting particle. This scale is a descending numerical scale from high to low (high number = rough/aggressive, low number = smooth/less aggressive). Thus, the lower the number the smaller the particle and, conversely, the larger the number the larger the particle. With this scale the higher the number is the rougher the abrasive is (i.e. 50 micron is rougher than 10 micron).

Think of it like pixels.Grit is the number of pixels in a given area and a micron is the size of the pixel itself.

And to make things more confusing and irritating in regards to the grading measurement of grit, there are several different international scales each having their own system. And of course the three main scales (JIS, Japan; FEPA, Europe; ANSI, U.S.A.) do not always directly relate to each other. For example, JIS 1000 = FEPA 400 = ANSI 500 = 18 micron. For a good conversion chart click here.

All companies use a sieving process to grade and size the cutting particles to be used in a given abrasive but each company uses a different process and each has it's own standards by which to grade. These differences result in inconsistencies between two abrasives of the same type and grit (or micron) if produced by different companies. In the case of some lower quality abrasives there are even variances between two abrasives of the same type, in the same grit produced by the same company. For these reasons it is always better to buy high quality abrasives from reputable producers as these producers test and process more thoroughly and they use higher quality cutting and bonding agents.

Bonding agents are the vehicles in which the particles of cutting material are suspended. They are as important as the cutting agent. It is essential that the bonding agent degrade at an appropriate rate in relation to the cutting material. This degradation is necessary because as the bonding agent degrades it exposes new, fresh, sharp cutting particles. If the bonding agent degrades too slowly the exposed cutting agent becomes blunt and ineffectual. If it degrades too quickly which is better than too slowly but is still not goodthe cutting agent is not used to it's full potential and is discarded prematurely. Thusly the abrasive product expires quickly and is not cost effective.

High quality abrasives with a good rate of degradation are especially important in regards to machine sharpening. As machine sharpening can produce a tremendous amount of heat very quickly, the exposure of fresh, sharp cutting agent is of utmost importance. With machine sharpening, The use of blunt or worn out abrasive should be avoided whenever possible. It is not always the case, but more often than not price is a good indicator as to quality. This is particularly true in the case of sharpening stones and abrasive papers or linishing belts.

Refinement with abrasives:

(To avoid further confusion, henceforth all discussion of abrasives will be in the measurement of grit)

Now that you know how abrasives are graded you need to know how they work. There are several main types of cutting agents used in abrasives that are especially well-suited for sharpening: diamond, silicon carbide, chromium oxide, aluminium oxide, silicon oxide, ferric oxide and hardened steel. Each has it's benefits and some are better than others on different materials, but they all do the same thing. Cutting agents all remove material by cutting. This cutting is accomplished by the cutting agent being harder than the cut material, thusly leaving scratches in the cut material as the material is removed.

So with that in mind, refer back to the grit grading scale: lower grit=bigger cutting particles = rougher = bigger or deeper cuts=less refined, but is more aggressive, resulting in faster material removal. Conversely higher grit = smaller cuts=more refined but is less aggressive, with slower material removal. Knowing the basic concept of grit and grading you can then begin the process of sharpening with a focus on the concept of refinement. That is, start with a low grit to accomplish the rough work (I.e. repair, reshaping of a bevel etc.) Then work your way through progressively higher grits, each progressive grit refining the scratches of the previous one until the desired final point of refinement has been reached. The more grits that are used in the process, the finer and more accurate the end result with less time and effort spent on each successive grit.

Now consider this process of material removal by cutting/scratching and it's effect on the cutting edge. This scratching leaves a pattern on the surface of the work and, once enough material is removed and the scratching reaches the edge, the pattern is mimicked in a saw tooth-like texture on the edge itself. Once this is created and as long as the surface is being worked, the texture folds back from the edge to the side opposite of that which is in contact with the abrasive and is known as a burr. A burr is remnant material still attached to the edge of the work. This phenomena, created by the sharpening process is a result of the abrasive compromising the crystalline structure of the steel as it cuts through it. As the structure of the steel has been fractured it becomes very weak and is why the burr bends from side to side and remains attached.

This is an area of contention between some sharpeners. A burr, being saw like is referred to by some as micro serrations. Some believe that these serrations ARE the edge of the blade and are a good thing as they provide great initial cutting but the fact is that the serrations are NOT the edge, are NOT a good thing and are in fact very weak.

Although they may initially feel super sharp, they become damaged easily and will ultimately result in an edge which will become more severely blunted more quickly.

The edge actually resides behind these serrations and the degree of edge bluntness that occurs once the serrations have become damaged relates directly to the size of the serrations. The size of the serrations in turn relate directly to the grit of the final abrasive used in sharpening. The lower the grit, the bigger the scratches are, which also means the bigger the serrations are. The larger the serrations are the greater the damage is to the edge once they have become broken or folded.

These serrations are always there regardless of the grit being used, you only need magnification strong enough to see evidence of this. It is for this reason that it is necessary to not only work through progressively higher grits in order to remove all scratching and tooth of the previous grit but to also take the sharpening to the highest possible grit which results in the finest possible tooth and therefore the least amount of damage to the edge once the tooth has broken off . The severity of damage through use can be even further reduced through the process of honing. Honing is the forced and controlled removal of any remaining tooth by employing any number of different techniques, all generally based on the same concept, and a super fine abrasive. In the process of honing the tooth is drawn (pulled) away from the edge using only edge trailing strokes on leather, soft wood, hard felt or some other similar material which has been impregnated with a super fine abrasive. Some abrasives used for honing are specially designed for the task (stroping paste, green chromium and others). However other more readily available abrasives can be substituted (rouge, various polishing pastes).

The abrasive cuts the hinge between the tooth and the actual edge helping to facilitate the removal. By controlling this process any damage incurred from the breakage of any remaining tooth through use is greatly diminished. Honing comes with a caveat however, that is, if the sharpened edge has not been taken to a fine enough abrasive before honing one of two occurrences may happen, neither being good. First, if finished to too low a grit all honing does is pull the tooth straight creating a very (initially) sharp but very weak and short-lasting false edge. This is very common and is more often than not the final outcome reached by most sharpeners. The second occurrence is if the edge is sharpened to too low a grit (or improperly sharpened) and then honed until the tooth ,which is still attached to the edge, is completely removed, in essence breaking the tooth off the edge. In this case what will remain of the actual cutting edge will be a slightly rounded edge with a very jagged texture that will feel sharp to the touch but will be extremely weak and will become blunt almost instantly upon use.

Then, even if the sharpener has done everything correctly and the sharpened tool has beenfinished properly there is still the risk of over honing. Because the act of honing uses a slightly soft or flexible material as the hone, what can happen is, as the hone compresses or flexes it curls up and over the cutting edge which can very easily cause the edge to become rounded. Sharpeners refer to this as rolling the edge over or "dubbing". The utmost care must be taken to avoid this result by 1) not applying too much pressure while honing, 2) (for the beginners) not using a hone which is too flexible, 3) not using a honing abrasive which is too aggressive, and 4) being sure to hone at an angle that is more acute than the angle that the knife is sharpened to . (I.e. if you sharpen at 20deg-ish hone at less than 20)too steep an angle will put too much pressure and abrasion on the edge and will roll it over. A rolled edge will feel sharp to the touch and may even shave hair but it is not truly sharp and if sliced through free-hanging newsprint will leave a cut with a rough texture and may not even cut the paper at all.

Note: the use of printer paper is not an accurate test as it is too thick and too tightly pressed; just about any relatively sharp tool will cut this paper.

Another technique for the removal of any remaining tooth is to cut a micro-bevel (or bevels) onto the final cutting edge. The act of cutting a micro-bevel requires extremely fine abrasives and the use of a sharpening jig. It is a delicate and extremely accurate process that is beyond most peoples willingness to either pursue or execute. In essence micro-bevels are microscopic bevels applied to the edge of a blade that are cut at progressively slightly steeper angles to the main bevel. The process of cutting micro-bevels cuts away any remaining tooth and the application of which are the ultimate in edge strength and durability. For a more comprehensive description of what micro-bevels are and how to execute them click here.

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Posted in Outdoor Activities Post Date 01/03/2016


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