Cosmo knives will last many lifetimes if cared for properly. To maintain your knife in its optimal condition, we recommend the following:
- Hand wash and dry your knife after use (do not use dishwasher)
- Clean the sheath and handle with soft damp cloth then buff with dry cloth
- Wood handles can be polished with furniture wax and buffed with soft dry cloth
- Protect the blade from contacting other metals in the sink, drawers, etc
- Protect the tip – the most vulnerable part of the knife; no prying, etc.
- Avoid long-term exposure to direct sunlight, intense heat and water
- To avoid instantly blunting your blade, avoid cutting on hard materials (ceramic, stone, glass)
- For the lifetime of your Cosmo knife it may be returned for sharpening at no charge for as long as Seth is able.
There are many ways to sharpen a knife depending on the tools you have available.
The first step is to visualize what is happening to your knife edge when the knife becomes dull. Imagine a dull knife, with a rounded over mushroomed, bent or worn out edge. Most blades have a primary bevel and a micro-bevel. It is the micro-bevel that requires sharpening.
The next step is to remove the rounded over edge by grinding the micro bevel to approximately 17 degrees, (if you are unsure of what that is imagine 90 degrees is upright half of that is 45 degrees and half again is 22.5 degrees, then just drop the blade down a few more degrees and that is close enough. Just remember the lower the angle the sharper it will be but the faster it will dull. Straight razors are approximately 5 degrees, whereas meat cleaver are around 22.5 degrees. This is one side so for total edge angle add both sides 17 X 2 = 34 degrees.
There are many different types of tools one can use to sharpen your blade. To grind away the worn out edge, use a medium to course sharpening stone. Don’t waste time using too fine a stone to start with. I have used tools as simple as a flat stone found on the beach. Other tools include oil stone, water stone, diamond laps, ceramic rods, sand paper, sharpening steels, stone grinder, or belt grinder.
If you have a knife steel, (note if it is old it is probably worn out), place the steel handle up point down on a cutting board. Place knife blade at 17 degrees to steel and drag it from heal to tip of blade working from top of the steel to the bottom.
It is not necessary to achieve a perfectly centred edge. Many knives are only sharpened on one side like a chisel (chisel grind). If it is a chisel grind it is best if the user grinds the micro bevel on the right side if the user is right handed or vice versa is left handed.
One of the biggest challenges is knowing when to stop grinding. That is what the wire edge or burred edge is for! You can see it with a bright light or feel it with a finger nail, make sure the wire edge is along the whole blade. You can also lightly drag a paper towel, or fibrous material over the blade. The wire edge will catch on the material.
The next step is to remove this wire edge. There are many ways to do this. This is called ‘honing’ the blade. THIS is where most beginners fail.
Here are a few ways to remove the wire edge.
Use a honing stone, it could be a water stone or oil stone, but it must be very fine grit. Raise angle approximately 1 degree (to 18 degrees) and hone edge till burr is removed, stop as soon as it is off. You know it’s off when you can’t feel it, see it and sometimes you will even see it floating in the media on the stone. Another common mistake, is too much honing and the edge is rounded off again. If this occurs and you were hoping for a razor sharp edge you will have to go back and recover the wire edge.
Another way of removing the burr is power buffing. This is a very fast and almost fool proof, but you need the tool. I would use a polishing compound and a cotton buffing wheel, edge facing down! Usually 4 passes or so is enough to remove the burr. Again stop as soon as the burr is removed, as doing more passes will only round off the sharp edge.
I have found that the best way to remove the burr for achieve the keenest edge is power stropping, using a leather belt on my belt grinder, and a little 50,000 mesh diamond spray, Again EDGE DOWN! Holding the same angle as for the sharpening, make approximately 4-6 passes on each side until burr is gone, this will produce the sharpest edge possible.
If you don’t have the luxury of the tools I have, a simple strop on a leather strip (belt) will work but harder to maintain the perfect angle and you with need to strop approximately 50 passes until burred edge has fallen off.
If you have some polishing compound apply to the belt, I have even used tooth paste rubbed into the leather.
Lastly, the direction of the grinding step is not important, if you feel comfortable making cycles, figure eights or pulling to pushing, these motions all work fine. The goal is to create a burred edge, and even in the honing step as long as you stop when the burr has been removed any and all directions will work in my opinion.
If you have questions or comments, please send me an email.
Stay sharp & enjoy,