Kitchen Knife Sharpness Confusion

[knightzerox23]

I have been sharpening my own knives for a while now and always felt I did a pretty good job and had very sharp knives.

Recently I went home and began sharpening my mom's knife which had been very dull. I've never sharpend a very dull knife and quickly went to the store and picked up a small coarse grade/ fine grade diamond combination "stone" ( not a real stone but just had diamond coated plates for sharpening ).

I sharpened it the way I usually do which but found it was having difficulty cutting into the skin of some green peppers. I normally start at a coarse grade and move up but found I had to stop at 750 grit to get it to really cut through well. Funny thing is I have this exact same knife at home and usually never have this problem.

I came home and started cutting some mangos I got from my mom and realized I couldn't break the skin with any of my knifes. After some experimentation this is what I found:

My normal way: 1000 grit then do 6000 grit ( knives with good edge already )

New way: 350 grit then 750 grit

I tested using the mangos, tomatoes and paper.

Old way cut through tomatoes and paper smoothly but not mangos.

New way cut through everything but not smoothly through paper.

I know that you should sharpen your knives depending on the purpose, but It seems odd I can't find a good balance. The rougher grit cuts through everything but on some things it seems not as smoothly. Also, if you only need to go to a very coarse edge knife, why go up to 1000 grit, 6000 etc? I know many people go up that high or higher to get a very polished smooth sharp edge.

Is their something I'm not doing when using the higher grits to get it to break the skin of tougher fruits?

When do most of you guys stop?

thanks for the help!

 

[Way-O]

for kitchen knives I use a fairly coarse cheap benchstone. I don't know the grits, it's two-sided and the finer side is something I'd rate a medium. But I guess some would say it's coarse. After I've raised a burr on both sides and thinned it as much as I can, I swipe it off with a fine Spyderco ceramic stick. It leaves the edge toothy, you can easily see the scratch pattern. But it also leaves a shaving edge usually, not that I really aim for that. My Felix Santoku got razor sharp almost by accident, cutting hair above the skin. It still kept the ability to bite into vegetable/fruit skins with zero effort.

 

[Cliff Stamp]

Also, if you only need to go to a very coarse edge knife, why go up to 1000 grit, 6000 etc?

For some cutting the higher polishes work much better. Peeling potatoes or chopping up a turnip works best with a mirror finish.

Is their something I'm not doing when using the higher grits to get it to break the skin of tougher fruits?

No, as you increase the grit you start to lose slicing ability on materials which have hard shells.

Some of the foods like over ripened tomatoes and plums are very difficult to cut clean because the flesh gives easily under the skin.

A knife has to be very sharp to cut those without squishing the juices. Very fresh bread is another thing which is very demanding sharpness wise.

I like Sharpmaker medium for most slicing work in the kitchen and Sharpmaker fine + CrO for peeling and dicing.

-Cliff

 

[knightzerox23]

Ah I see. Thanks for the clear up!

 

[Jeff Clark]

Nature makes many materials that are held together by fibers. Hair, animal skin and skin on fruit are all rather tough for their thinness. Often these thin tough fibrous covers protect a soft and complient material. If you push down on the outside you can squish the inside without breaking the skin. The skin tends to shape itself to match whatever is pushing on it and the soft inside material also moves around to fit the shape of the external object applying pressure. To cut through the skin without crushing the insides there are a couple of tricks that help. One is to start a cut with a point. A point will overstress a very small part of the skin to get a cut started. A serrated blade or a very roughly sharpened blade looks like a series of points on a small scale. You may find that you could press one of these edges into your fruit with less effort than a smooth edge. An even better trick is to take a serrated or roughly sharpened edge and draw it across your fruit. The serrated teeth and the micro-teeth of the roughly sharpened edge will cut into the skin crosswise rather than down. The skin cannot stretch as much crosswise and is more easily overstressed by slicing strokes. You need little teeth to gouge into the material for this. The softness on the inside of the fruit will be less of an issue since you are using the strength of the skin itself to keep your cut surface still while you slice.

In the kitchen I like to finish some of my knives with a medium ceramic rod for slicing and a fine ceramic rod for general purpose cutting. This leaves the edges with a little 'tooth' for slicing.

 

[knightzerox23]

Thanks for the replies again!
Everythings is clearer now.

Makes sense that mangos have a fiberous skin which makes it tougher to cut than a soft tomoatoe skin.

I will probably take my everyday knife and give it a polished edge since most foods I cut are soft. As for the mangos, I'll try using the point to break the skin first and then slice.