Tuesday, January 7, 2014

Blog 62: How to Sharpen a Knife

By Cliff Jacobson

It’s easy to sharpen a knife.  All you need is a whet-stone, some honing oil and practice.  You can use a diamond stone or a natural stone.  No matter: any good sharpening stone will work if you do your part. Indeed, South American natives sharpen their machetes on the side-walk and they obtain a very sharp edge! This method works with any non-serrated blade:

1.  Electric and mechanical sharpeners will provide a good working edge but not a wickedly sharp one.  If you want a razor-sharp edge, use a whet-stone!  
2.  Don't ever use a grindstone on a good knife!  You’ll destroy the edge and the temper.Those handy "pull-through" sharpeners designed for kitchen knives will produce a quick working edge, but not a super-sharp, polished edge you can be proud of.
3.  To obtain a fast "working" edge on a dull knife, begin sharpening with a coarse diamond stone or coarse Carborundum or aluminum oxide stone (available at hardware stores).  A fine-toothed file can be used to remove deep nicks in an abused blade or, to re-form a blade that has a broken tip.
4.  Once the edge takes shape, change to a medium grit "soft Arkansas" or "Wachita" stone.  Keep the stone well-lubricated with cutting oil, WD-40, or kerosene.  Do not  use automotive or gun oils! 

5. Diamond stones come in coarse, medium and fine. A coarse stone will take off metal real fast--ideal to set the edge of a new knife.  But once the edge is "set" you'll probably never again use the coarse stone.  Sharpness will be easy to maintain with a "fine" stone.  The point is that you will get far more use out of a medium and fine abrasive stone than a coarse one.  If you want to save money, buy a coarse carborundum stone (hardware store) and use it for tough sharpening jobs. When the nicks are gone, go to a medium grit diamond stone. Finish on a fine Arkansas oil stone. A fine oil stone will produce a highly polished, razor edge.
6.  Sharpening will go easier if you dip the cold blade into boiling water for a few seconds before you begin to hone.
From: Camping's Top Secrets, by Cliff Jacobson. For most camp chores--cooking, whittling, etc., a 15 degree angle is best. Twenty degrees is better for knives that will be used hard (cutting into bone, heavy gristle, etc.)

Maintain a film of light oil (natural stones) or water (diamond/carborundum, and aluminum oxide stones) to float away the steel particles that clog the pores of the stone and reduce its cutting efficiency.  Every few dozen strokes, dry the stone and blade and apply new oil. Yes, you will go through a lot of oil this way, but you won't dull the edge by grinding metal shavings into it.  Frequent cleaning is essential if you want a super-sharp edge! You don’t need to use a special cutting oil—WD-40 works fine.
The "penny angle" trick works only with a narrow blade like that on a Swiss Army Knife.
Keep the back of the blade raised 10-20 degrees and cut into  the stone as you sharpen. If you have a Swiss Army knife, you can approximate the correct angle if you rest the back of the blade on two stacked pennies (photo 1).  Another trick is to set the blade flat on the stone and adjust a bright light directly overhead. Slowly raise the back of the blade until you can just see a shadow.  If you want a whisker-sharp edge for slicing food, use a shallow (about 10 degrees) angle. For more rugged work, 15-20 degrees is best. You MUST maintain the precise angle as you sharpen. Most people need about 30 minutes of hands-on sharpening practice to build the muscle memory needed to hold a consistent angle. You MUST maintain a consistent angle or your knife will never get sharp!

You can buy special tools that maintain the recommended angle as you sharpen.  These tools clamp to the knife blade.  They work well on the body of the blade but not on a sharply curved tip.  If you learn to hold a consistent angle by hand (it just takes practice) you'll never use a clamp.
This is a medium grit Arkansas stone. Generally, carbon steel blades like this old Case knife, will take a faster and keener edge than stainless.  
Take about six strokes per side on the stone. Keep the stone flooded with lubricant.  If you want a razor’s edge, switch to a fine-grained stone (natural or diamond), then finish by stropping the blade on a leather belt. Strop the edge away from the leather, not towards it as  when using a hone.

            There are many ways to check blade sharpness.  Here are a few:
  1. A razor sharp knife will shave hair from the back of your hand.
  2. Shine a bright light on the sharpened edge. A dull edge will reflect light.
  3. Drag your thumb nail lightly across the blade.  The blade should scrape the nail cleanly, without chattering.
  4. A razor-sharp knife will cleanly slice typing paper.
Note:  A sharpening (butcher's) steel will not sharpen a knife. A steel is simply a coarse version of a leather strop. It’s for touching up a well-used blade but it won’t take the place of a whetstone.

Cliff Jacobson


1 comment:

Knife Sharpener said...

Really a great blog with a best thoughts and ideas are shared thanks for sharing such an interesting article.

Knife Sharpener