How to sharpen your knife - 6 secrets of a knife maker April 22 2014, 0 Comments

 All knives are going to get dull sooner or later, they will lose their sharp edge over the time of use. With some knives this goes fast with others fairly slow. Why do we have these differences? And how do we address them when sharpening our knife.

Here are some insider’s secret tips and basic ideas of what to respect when sharpening a knife:

  1. Analyze how you use the knife: chopping, push cut (like a razor) or pull cut (like a butcher knife, the most used cutting activity in a knife).
  2. What steel does the knife has? Stainless steel, carbon steel; low, medium or high grade steel. It helps if you know about its toughness, wear resistance, hardness etc.
  3. Analyze 1-2 and follow the matrix. Use steel proposed sharpening angle/edge geometry. Chopping low/medium grade CS or SS + 30 degree sharpening angle, no fine edge as the edge has to withstand the chopping impact. Push cut you should have the highest grade 16 -25 degrees as this cutting application CS or SS for this application requires a very fine edge.Pull cut all steels cutting angle + 25 degrees.

    A rule of thumb is that for to cut harder material (wood etc) you use a steeper angle and a finer for softer material like meat. This will make your edge stand longer on the wood part and cutting easier on the meat part. The general use of an all purpose knife will be mostly pull cut but also some push cut. If you can’t find the original angle of the edge, stick with the 25 degrees.
  4. What bevel does the edge of the knife has, flat ground, hollow ground, convex ground, scandi grind etc.
  5. Choose the right sharpening medium. Here comes not only the given edge geometry in play but especially the steel in the knife. Some sharpeners won’t work on all steel, as a rule of thumb as higher grade the steel as more sophisticate the sharpener. Generally a stone is preferable to everything else. Use a high quality stone, grit size should depend on your sharpening needs, coarser for sharpening an axe, very fine for a straight razor or kitchen knife. For knives start with a medium grit (~ 1000 grit) stone for the stock removal and fine grit (3000-4000 grit) for the fine edge. For very sharp knives go to 10,000 grit and finish with a strop. Make sure the stone is always flat, no dips, belly’s or hollows allowed! (see our article http://www.terrierblades.com/blogs/knife-sharpening/15717251-knife-sharpening-sharpening-your-knife-dull )

  6. When sharpening, clean the blade and wet the stone (oil or water as recommended). Put the blade on the stone with the EDGE touching the stone. You will want to move the edge against the stone. Before you move the blade on the stone, wiggle the edge a bit to find the angle of the sharpening bevel, you want to mimic the original edge geometry/degree of angle. This is easy with flat or scandi grind; hollow grind and dual angel flat grind have only the small final edge angle which might be difficult to find, some praxis helps.

    It is very IMPORTANT to always have the correct/same angle when moving the knife on the stone, so use a guide which can be your finger or and edge guide like some of the sharpening kits have.

    Use the medium grit stone till you have all the dents etc out of the edge. Switch to the fine grit stone and use the SAME ANGLE as you did on the medium stone. Finish this step when you feel real cutting on the edge, for the paper fans you should be able to slice a paper but might get some rough cut.

    To achieve a very fine edge go to a finer grit stone and after that, hone the edge. To hone the edge use a strop, usually leather with some compound you can put on it. Now we change the move! You are not going against the edge anymore, you move with the edge like touching up a razor (if not you’ll cut the leather). The edge should get a polished sheen on it and now you’ll be able to slice paper nicely and shave your arm. Honing can also be used to touch up a very sharp edge.

 

A final word to the steel: As higher grade the steel with high toughness, hardness, wear resistance etc as more time you’ll need to do the manual re-sharpening, but as less often you have to do it in the trade-off. Very high grade steels will not tolerate a sharpening or touch-up steel as butchers use, you’ll need ceramic, some diamond will do.