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The Cutting Edge… Part Two: Putting an Edge on the Edge

12 Dec

San Diego –OK, here is part two; the “how to sharpen” segment that was supposed to be in the first part before i got off track…

There are those who will happily tell you of their expertise in this topic, i.e. sharpening knives.  I’m not one of them.  I claim no special expertise because it truly is not magic.  But I do like to have all of my edged instruments appropriately very sharp based on their functions.  And I do know how to make that happen, thanks, not to any intuitively masculine insight, or having served as a novitiate under an inscrutable master of the blade, but rather to the help and guidance of some people that have crossed my path who truly were experts at it.

A number of dinner guests have commented on the sharpness of the knives and asked where I get them sharpened.  When I tell them I do it myself on my workbench I often get requests to show them how or even to do it for them.  I will happily take one of their knives and show them how so they can then sharpen their own knives.  And it is easy if a little time consuming.  But since you pay a good price for good knives, it only makes sense that you would want to keep them doing what they were designed to do…cut well.

There is neither time nor space here to get into the details of why different tools need different types of steel, varying degrees of sharpness, and different sharpening bevel angles based on the need for cutting power versus edge durability. Harder steels can take a sharper edge and hold it longer (though they are harder to sharpen in the first place) but with hardness come brittleness and a very fine edge of very hard steel is easy to nick and damage.  Softer, higher carbon steel sharpens more easily but has to be kept free of rust and it wears faster.  You decide what works best for your own needs.  There are lots of web pages devoted to providing this information so you can make an informed decision.

In terms of bevel, surely it is obvious that a true razor’s thin edge would not last very long on an axe used to chop and split wood.  There is some confusion by many over the terms “razor sharp” and “shaving sharp.”  Any edged implement from an axe to a filet knife can be made sharp enough to shave hair and therefore be “shaving sharp” but only a razor truly benefits from the extremely thin angles of grind suitable to a device that ONLY exists to shave hair (picture a razor blade here).

For all edged devices however, the sharpness is a function of how thin the material is at the very point of where the sides meet.  But how well they perform their job depends not only on their being sharp, i.e. the cutting edge coming together to form a very fine point, but on the type of angle created to make that point.

For a long time hollow ground edges were considered among the sharpest because the two concave sides created a very fine cutting edge.  Some knife makers made an advertising campaign out of it.  And yes, it is a very sharp edge.  But that shape not only creates a very vulnerable point unless the material is very hard, it also creates a lot of friction and drag as it cuts because of the way it forces the tissue being cut to expand.

So in use, the hollow ground edge sometimes seems to be duller than it actually is.  Consequently, at least at the cutting edge itself, most modern experts to not seek to create a hollow ground edge although some knife designers use it on the central blade to reduce weight and actually strengthen the blade like a giant ‘fuller’ (often mistakenly called a “blood groove”) but then allow it to thicken out toward the edge for proper sharpening.

Most good blade sharpeners these days use either a flat ground edge or a convex ground edge, the latter being the one experts strive for as the sharpest, longest lasting, and providing the best cutting power, but which can only be done consistently and properly using a flexible belt sharpener (more on this later).  Sharpening using a set of stones produces a flat ground edge, though many experts simulate a convex edge by creating a multiple angle flat grind.

The key to sharpening anything is to keep the angle of grind absolutely constant through the entire process.  In all cases, the process follows a standard workflow:  (a) Define the edge, (b) create the burr, (c) remove or align the burr, and (d) polish the edge.  In, practice although one may go through 3-5 or 6 grits of stone or abrasive, is a three part process:

(1) Define the edge,

(2) Sharpen the edge, then

(3) Polish the edge.

Step one is the most destructive and is done only when absolutely necessary due to blade damage or abuse.  It ends up removing a lot of material and over time thins the blade.  A new knife has the edge already defined and unless you want to repurpose it, if you keep it sharp and do not damage or abuse it, keeping it sharp does not remove very much material.  It is so much easier to keep a knife sharp than to sharpen a dull one!

Defining the edge is done with a very coarse stone such as a carborundum or course abrasive stone of about 80 grit, or sometimes, if a lot of work is needed, even a file.  I know the mere mention of a file will set modern blade experts’ teeth on edge but I can tell you from experience that farmers and outdoors people have used them to quickly redefine an edge or to remove material when an tool’s edge was seriously nicked.  But like subsequent steps, great care must be taken to maintain the angle of the edge and not to rock the stone or file.

Most experts will advise you to NEVER use a power grinding wheel unless you have LOTS of experience with it.  There are VERY good reasons for the advice.  Not only will it completely ruin an edge shape in micro-seconds if you slip, but, and as importantly, it heats the fine edge so rapidly that you can destroy the temper.

With care, experience, a good eye for angles, and an extremely steady hand, you can do the edge defining freehand.  But the best thing is to use a sharpening angle guide to maintain the angle.   Most people have a very hard time not rocking the blade during a sharpening stroke and that is the major cause for problems and lots of effort being put into creating very unsharp knives.

To make explanations of the process simple, lets start first with a simple flat ground edge.  If you only learn to do this and keep the knife sharp it will be shaving sharp and quite good for most uses: better, in fact, than you may have ever been used to.

The precise angle/bevel is different for different types of knives.  For heavier outdoors, camping, ‘hunting’ and general purpose knives the normal angle is about 25 degrees on a side.  This creates a strong edge that will stand up to cutting and light chopping of wood and rope or whatever is needed.  Kitchen knives are often set at 15 to 20 degrees on a side and specialty knives like filet knives or skinning knives, if the steel will allow it, might be as shallow as 10-15 degrees on a side.  Just remember, while the thinner blades are sharper, that thin grind has weakened the edge and leaves it far more vulnerable to damage.  So while you could create such an edge on anything, it is generally relegated to blades that are only expected to cut into soft items.

And remember too; if you are changing the sharpening angle of a blade from what it was previously to a thinner angle then you are (re)defining the edge and have to remove some material from the main portion of the blade itself and not just around the edge.  And in doing so you are committing that knife to the sort of service appropriate to that blade and edge configuration.  Also remember that a very sharp knife of any type will cut you with virtually no effort or pressure applied so learn to handle them correctly and safely.

So what do you need to sharpen your knives?  You can do it with a good set of sharpening stones ranging from coarse to medium to hard; or you can purchase one of several sharpening aides or even sharpening devices.  All of them work; but a blade, even a newly sharpened one, is only as good and durable as you treat it so if you are not willing to learn to treat your knives properly you probably need some device to let you make easier work of the constant sharpening you will have to be doing.  More on this at the end.

OK, let’s get started.  Recall the process work flow from above.  All of the steps are done almost identically; the difference being in the progression from a coarser stone or abrasive to ones that are very fine and hard.  So back to step one.

Using the proper angle, stroke the stone, pushing the blade forward on the stone as if you were slicing off a piece of stone.  To do it properly the stone should be at least as long as the blade of the knife.  If the blade is VERY dull or you need to remove some nasty nicks then give it 5-10 strokes on a side then turn over for the same number of strokes so you can keep the bevel even.

WATER OR OIL OR DRY?  This is as good a place as any to insert the controversy about using lubricants on the stone.  The general wisdom for centuries was that using oil or water on a stone helped to float the debris from the grinding away and this is true.  But left to sit it also clogs the stone so after use it needs to be cleaned and dried.  A lot of modern experts prefer water but old timers still swear by oil.  Once you have oiled a stone it is now a committed oil stone.  Clean them with paint thinner, let that dry, then put the stone away where it is protected from dust and such than can settle on the surface.

However… one of the worlds leading experts on edged weapons and sharpening swears that his tests prove a dry stone cuts faster and cleaner although the stone does need to be kept free of the debris by brushing during the process.  I have tried them all and you know what? They all work.  The key is in maintaining the cutting angle and keeping the stone clean far more than what type of lubricant, if any, you use.

As the two edges of the bevel start getting close enough to meet at a point, cut back to 2-3 strokes then check for the creation of a burr by running a finger from the flat of the blade toward the edge on the opposite side from the side being honed.  This burr is a thin crest or wire of steel created as the two edges meet and is a sign that the bevel is at a true point.  It will appear on the side opposite of the one being honed.

Turn the knife over and give it another 2-3 strokes.  The burr should now be on the opposite side.  Check to make sure.  Now flip the blade again and lightly give it a stroke to remove the burr.

ABOUT THE BURR… Creating the burr is a necessary part of sharpening.  If it does not form it means the two bevels have not met at a point.  But there are two opposing schools of thought as to what the sharpener should then do with it.

There are those who believe that you ought to make use of it.  On the final honing strokes they advocate drawing the blade across the stone away from the edge to actually align the burr with the centerline of the blade.  The result truly is, for a moment, an incredibly sharp, micro-serrated edge.  With it you can shave enough patches on your arm to look like you have an acute case of mange.

But when you do any serious cutting or chopping, that incredibly fine burr simply folds over and, in effect, dulls the edge.  To blow away onlookers by shaving slivers from the edge of a paper towel or creating paper thin slices of tomato, use and polish the burr for a scalpel sharp but incredible vulnerable edge. 

But for serious use of a knife the majority of expert knife sharpeners work to eliminate the burr and then polish the real edge to a very fine, smooth point.  That is nearly as sharp and it lasts a lot longer.

OK, back to the process…

If you looked at the blade under some magnification it would look like it was serrated from the grit of the coarse grinding stone.  The next step is to remove those serrations.  If the edge did not need redefining, you would be doing exactly the same with a finer stone but the serrations would be finer.

Now go to a medium grit stone or abrasive of around 200-300 grit. And do exactly what you did to define the edge.  This second step is really the sharpening step. Same angle, same approach though some recommend now using a circular motion on the stone to help polish away the scratches from the coarser stone.  You will see the coarser “scratches” start to disappear into finer ones.  Once again when you have raised a noticeable burr.  Now use the slicing stroke and by use increasingly lighter alternating strokes remove the burr.

And now go to the even finer, harder stones finishing with a hard ceramic stone, doing with each precisely what you did from the first and making sure the angle of blade to stone remains constant.  When you have finished with a hard ceramic stone or a 6000 grit abrasive, you will have a mirror polished edge that will shave with the best of them but also have a useable edge.

This has created a flat grind edge and is the most common and easy to produce edge.  It can be very sharp but has a few drawbacks.  It does not wear as fast as a concave edge but it does still wear under normal use.  And as it wears, the resulting sharpening requires you to subtly but continually redefine the edge and wear down the blade.  So many knife sharpeners who use stones in their work, use a multi-angle bevel.  It is very similar to the flat grind in approach and work but adds some steps.

First it starts with a much thinner grind, say up to 5 degrees thinner to create the initial bevel or what is sometimes called the “relief” of the blade.  This does not have to be ground to a burr but it has to come very close and it needs to be finished as if it were the final edge unless you do not mind the rough look of the coarser stones.

When the relief has been formed, now increase the angle up to 5 degrees and, starting with the coarse stone and working through to the final polishing stone, create a new but very small primary cutting edge; creating then removing the burr.  Because it is not quite so thin it will last longer and it can be rehoned quite a few times before the relief bevel needs to be reground.  Additionally, the now slightly convex shape tends to cut through meat with less friction and resistance than the concave grind or even the flat grind so it seems to be even sharper than it is.

Because of this some really serious sharpening addicts use a three step bevel but you need really very good and precise angle guides to do this.  And you can see where this is headed: based on the additive quality of this increasingly convex edge shape, the ideal is a truly smooth convex grind.

I’ve read that some experts claim they can do this on flat stones with demanding control but I confess I cannot do it and end up just dulling the blades.  Multi-angle I can do but smooth convex is something my old hands cannot properly control. And the truth is, the professionals who adopt this approach don’t try either except perhaps to blow away the apprentices.  What they use is a flexible belt sharpener.  With the proper spring tension on the belt there is just enough “give” to allow for a controlled convex edge all the way from coarser abrasives down to polishing belts.  Finished off with a light touch from a cotton polishing/buffing wheel and this creates a stunning edge that is longer lasting than the others and cuts more easily as well.

Of course, all edges wear and need attention.  Keeping the knife sharp by simply repolishing the edge after use will keep it sharp a very long time before you need to actually resharpen it.  But normal cutting chores are not all that work to degrade the edges on your knives.   You can prolong the need to resharpen them by paying attention to these care tips.

Cutting on hard surfaces will dull a knife faster than nearly anything else so always, ALWAYS use a chopping/cutting block or board.  Obviously the dining table “steak” knives are always used against the ceramic plates to they need the most constant attention of all if you want to keep them sharp.  And believe me dinner guests will notice and comment when their steak knife cuts the meat like a hot butter knife through whipped butter.

Do not – repeat – DO NOT wash them in a dish washer.  Setting aside the damage to wood handles, it would take up a lot of space for a complete explanation so please, just trust me here, hand wash the knives in mild detergent, rinse thoroughly and then proceed as below to store them.

Cutting acidic foods like tomatoes will degrade a fine edge so be sure to wash the blade off with hot soapy water, rinse well and dry with a towel before putting them away.

And when you put them away do not just toss them in a drawer full of knives!     First, after cleaning and drying use a paper towel and apply a very light coating of cooking oil to the blade to hold back rust.  Yes, even stainless blades will get micro rust particles on the very edge and start to dull just sitting there minding their own business.  Some people advise against using cooking oil since if it sits long enough it can go rancid and smell.  My knives do not sit long enough for that to happen and since they are washed before and after use that fear has never come true for me.  If you use something other than cooking oil (honing oil, light machine oil like 3-in-One™ is good), you need to make VERY sure it is all washed off before you use the knife to cut food.

Then put the knives into a block.  If they must go in a drawer, at least protect them with the cardboard “sheath” they came with.

SHARPENING APPLIANCES:  Finally a quick word about knife sharpening appliances, especially those that basically make all of the decisions for you.  I have used a lot of them in an attempt to find something to recommend to friends who seem unwilling or unable to properly sharpen their knives using whet stones.  Nearly all of them will produce a serviceable edge of you use them exactly as instructed and all of them are better than nothing.  I have a few of them stashed around such as in my car, motor home, backpack, etc. for quick in-the-field touch ups.  Some are better than others but none of them will produce the quality of edge that you can get yourself if you are willing to take the time and learn to do it right.

And I have to mention that ubiquitous kitchen device, the steel.  Those are designed to be used by butchers to quickly straighten out and realign little areas of rolled over edge that hit bone or something dense.  They are to keep the blade going a little longer and not… NOT… sharpening devices.  And unless you can hold a perfect angle of blade to steel you will do far more damage to your blade than good using one.  Leave that to the people who know how, and when, to use it.

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Posted by on December 12, 2011 in Uncategorized

 

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