Instructables
Picture of Sharpen A Knife Quickly and Easily
If you have a carbide tipped saw blade, you have an excellent tool for sharpening a knife quickly and easily.  Just clamp it to a tabletop or lock it on your saw's arbor so it cannot turn.
 
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Step 1: Draw the knife edge against a carbide tooth

Picture of Draw the knife edge against a carbide tooth
Draw the cutting edge of the knife against a front corner on a carbide tooth.  You do not need to use a lot of pressure.  A few repeated passes will do wonders to a blade.  The green lines represent the angle of the tooth face and the angle at which the blade is held.  The brown lines represent a vertical line and the angle from the vertical at which the knife is drawn across the corner of the carbide tooth.  Draw the knife slowly.  Hold the blade with two hands to keep the edge on the relatively small corner of the tooth.  

Step 2: Do the other side

Picture of Do the other side
After a few strokes on one side, turn the knife over.  Use the same angles relative to the carbide tooth that you used for the first side, but draw the knife from the other side of the saw blade.  Alternate sharpening one side of the knife blade and then the other every few strokes.     

Step 3: Test for sharpness

Picture of Test for sharpness
I have often seen people pull a knife edge across the soft skin on a fingertip.  That is a sure way to receive a cut.  Much better is to scrape the blade laterally on a fingernail as shown by the green arrow.  If the knife is sharp, a curl of fingernail will roll up in front of the cutting edge.  If the knife is not quite sharp, powdered fingernail will gather in front of the cutting edge.  If the knife is quite dull, nothing will appear in front of the cutting edge.  Test at various points along the length of the cutting edge.  Some parts of the cutting edge will be more dull than others and will need more attention.
BARKing9 months ago

I have used the commercial carbide sharpener set in a V and found it removed a lot of material fast, great for knives that should have been sharpened long ago or just need to be trued up quick. I would not want to use it as my first go to every time i sharpened my knife as the knife would disappear faster than necessary. It also left it almost serrated as cojonc mentioned, which is great in the kitchen but not so good in the wood shop.

Phil B (author)  BARKing9 months ago
I would agree. The commercial carbide tipped knife sharpener I saw was a simple bar of steel with one piece of carbide on it, which allowed adjusting the angle and the pressure. We bought a sharpener ith to pieces set in a V like you describe to use in another location in a pinch. The single piece sharpener is more gentle.
gossumx4 years ago
Good idea, but why are you purple?
judging by your picture, I don't think you have much room to question someone's color
HAHAHA, it is the makeup color, Bob. Very good note.
Phil B (author)  gossumx3 years ago
Thanks. Poor lighting coupled with inadequate photo correction software.
Phil B (author)  Phil B3 years ago
I worked on the photo and made it a bit better.
cojonc3 years ago
It doesn't do the saw blade much good however.
Phil B (author)  cojonc3 years ago
I have not done this often, nor on the same tooth. I cannot perceive any degrading of the saw blade. Commercially available sharpeners are often two pieces of carbide set in a "V."
cojonc Phil B3 years ago
You are probably correct.

I often look at things microscopically as I did after using one of my blades to test your sharpening methods on a knife. To my amazement, the crisp edge on the carbide had changed. The steel in the knife I sharpened was harder than I initially thought, and rounded the carbide. Microscopically yes, but damage was apparent. The knife blade was also damaged as the sharpening attempt caused chattering creating nicks and lands. While this created somewhat of a sawtooth effect and the knife still cut, it would not "pressure" cut. It had to be used in a sawing action. Most will not understand this and I won't elaborate. For most, lets say it will probably work. It depends entirely what level of "sharpness" one considers workable. Most of the people I know have very dull, very dangerous blades. I am certain my standards are different, and more scientifically driven than the average person.
Phil B (author)  cojonc3 years ago
Interesting. I saw the knife sharpener I mentioned in a store and thought I could do that with a saw blade. The blade I showed is an old framing blade I do not use much. I expect the tips do most of the cutting, and they are untouched in all of this.
rimar20004 years ago
CLEVER! You are a born creator, Phil, always you seek and find a new solution to old problems.
Phil B (author)  rimar20004 years ago
Thank you, Osvaldo.

One day several years ago I was in a hardware store. Someone local was making knife sharpeners and the store was selling them for the maker. They were a piece of steel about 8 cm long. A carbide tooth for a saw blade was brazed onto one end. I thought I could just stroke a knife along the corner of a tooth on a carbide tipped saw blade and save $8. It worked.

This evening my wife asked me about the Instructable she knew I posted today. After I explained it, she had me sharpen her favorite kitchen knives with the saw blade in the photo. It worked very well.
hyratel Phil B3 years ago
+1 for DIY to the rescue
Rick_cae3 years ago
Very good idea. Haven't tried it yet but could you put 2 blades together (reverse angle forming a "V") and sharpen both sides at once?
You can use the bottom of a ceramic coffee mug too.
Phil B (author)  fridgewrestler3 years ago
Yes, you can, although that is a much slower method and leaves a black mark on the bottom of the mug.
neffk3 years ago
Does the carbide remove bits of metal from the knife edge? Or does it simply straighten the edge, like a "steel"?
Phil B (author)  neffk3 years ago
The carbide is very hard and the sharp corner does scrape metal away. I spent a week away from home where there are no saw blades. While there I bought a commercial sharpener that uses two pieces of carbide in a sharp "V" arrangement and used it over a counter to sharpen some very dull kitchen knives. There were light metal filings on the white countertop. I could pick them up between my fingers and felt their rough, granular quality. Thanks for asking and for looking.
Kryptonite4 years ago
Nice, I would have never thought to use a carbide blade!
Phil B (author)  Kryptonite4 years ago
Thank you. I would not have thought of it, either; but I mentioned to Rimar (Osvaldo) in the note below that someone was selling a piece of steel with a carbide saw tooth on it as a knife sharpener. I decided I could use a carbide saw blade.
I wouldn't have made the connection, personally. :P