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Everything you need to know about sharpening knives

By Vic Hamburger,  Mon, 10 Nov 1997

I keep seeing comments in articles and in discussions about always using a sharp #11 Exacto™ blade while working. My other hobby is woodworking (I should take up something cheap like yachts and sports cars!) and I do a lot of woodcarving. I beg to differ about the definition of sharp when it applies to cutting edges. If you want to learn some fast secrets to sharp edges, read on, otherwise scroll past this message.

I have the same 5 pk of Exacto blades that I bought many years ago….and haven’t used them all up yet. This is not to slam Exacto or put them out of business, but there is sharp as delivered by Exacto and other hobby knife suppliers, and there is sharp as I work. I promise you that once you try my methods, you will be happier with the quality of the cutting edge you get. Exacto makes an excellent, affordable product that you can sharpen to exquisite sharpness in a few minutes.

Good news is, you probably have everything you need around the house or can get it at the local hardware store. And you won’t spend more $$$ on this than you would a couple of packs of new blades. Still interested? Lets get started…..

What you need to get:

  • Some wet/dry sandpaper in grits of 320, 400, 600, 1000, 1500 Mostly you will use the 600 and up once you get the blade polished.
  • A piece of old, smoothish leather, the back of a belt works fine or get some hew leather scrap from somewhere. 1-2″ wide, 6-8″ long is fine.
  • Red Rouge polishing compound. Usually sold as a stick, one brand I use is Dico brand. $2-3 in hardware/automotive stores.

When you get fancy and want to start modifiying blades to suit yourself, get a diamond sharpening stone from DMT. Your hardware store will probably carry those. the mail order tool shops mostly have them also. the small stones in a leather case is about 1″ x 5″ and costs about $20. I recommend the red, fine grit stone for most work.

What a sharp edge looks like….. 8^)
If you magnify the cutting edge of a blade, you will see the blade is a flat piece of metal with one or both edges ground at an angle until they intersect at the cutting edge. The grinding process leaves a series of very fine ridges and valleys parallel to each other and perpendicular to the blade usually.

The idea is to reduce these ridges and valleys until the blade is super smooth along this ground area leading up to the edge. Start with a blade in the handle and the 320 grit paper supported on a board or other flat raised surface. Hold the blade at an angle so the ground edge to be flattened is flat on the paper. You then stroke this blade, EDGE TRAILING along the paper several times. It may take 10-30 strokes to get the edge uniformly smooth and dull. Do both sides of the #11 blade, or the single edge of other blades as needed until smooth and dull. DO NOT ROCK THE BLADE as you do this. You don’t want to round this flat edge, just smooth it out.

Once done with this grit paper, go to a finer grit, either 400 or 600 grit. Do the same for each grit, getting finer and finer until you have a very smooth dull finish on the two flat surfaces you have been working on. Once you get a blade polished like this, you can use the 1000 or 1500 grit to touch it up when needed. Mostly I just touch up a blade with the next step, leather stropping.

BTW….at this point, if you are sharpening a blade with one ground edge only, turn the blade over onto the side that was flat metal, and give it a couple of swipes on the finer grits of paper. This will remove any raised “wire” edge that develops when using this technique. You will want to polish this side as well.

Ideally you should glue the leather down to a piece of wood. This keeps it from slipping around and if you leave extra wood, you have a place to hold onto when stropping. Open the tube of red rouge and use course sandpaper to scratch off some sprinkles onto the leather. As you use the leather over the years, it will get darker and smoother. when you have a dusting of rouge on the leather, strop the blade the same as you did for the wet/dry paper, that is, EDGE TRAILING. I strop 10 times for one side, then 10 for the other edge. Then 5 times and 5, then 2-3 each and I am done.

Again, if the blade has only one side that you have been honing, hone the flat side as well with a few strokes when done to insure a smooth finish on that edge.

When you get thru, don’t try shaving the hair off your arm, try looking at the blade with the edge toward a light where the light could reflect off of any dull spots on the cutting edge. If you see a dull spot, you will need to go back to the w/d paper to get rid of it. Rightfully, you will see NO reflection back off the cutting edge. If you see no reflection, you are probably sharp and ready to use. Try cutting a bit of lightweight paper. If it cuts with no snags, you are sharp!

Always use a cutting mat (quilting section of any store that sells crafts or quilting material) or a piece of masonite to cut on. The blade will last longer and not run away on you like it could when cutting on a wooden surface.

Now, why did I go thru all this with you and what does it buy us as narrow guage modellers????

I _know_ it is easier to cut any modelling material with a really sharp blade than a new hobby knife blade right out of the package. A properly sharpened blade does not drag and catch like even a fresh blade sometimes can. The smoother the finish on the 2 edges that make up the cutting edge, the better the cut will be. We tend to only use the very tip end of the #11 blade, maybe a bit more with other blades. These will all last longer for you with an initial honing and regular sharpening. As I said before, I find I can work for days with just touching up the knife blade on the leather strop on a regular basis. Once the stop has some rouge working into it, you don’t even need to add rouge everytime.

I hope this helps with your modelling! If you are unclear about this, let me know….

Vic H

PS: Next installment, modifying blades and making permanent handles for them.

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