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My grandpa bought the Shapton Glass Stone 1000 Grit 5mm to sharpen his WÜSTHOF 4596-7/20 Classic Ikon 8-Inch Cook's Knife.

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He educated himself a whit by watching YouTube videos, and his sharpening has yielded metal shavings onto the Sharpening Stone. He tried to cut squashes with it, but it hasn't become any sharper! Why?

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    Fundamentally, that stone will sharpen that knife with the proper technique. I would assume something about his technique is to blame. If you can update the question with as much detail as possible on his technique, that might make this question more answerable.
    – AMtwo
    Jun 17 '20 at 4:11
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    First is to pay attention to the angle. Unless the knife is badly worn and needs some serious grinding, you should use a slightly steeper angle than the original edge. Also 1000 grit is kind of on the rougher side so your knife will be only be good for "push cut" (push forward while pressing down). You need to refine it with a finer stone to enable "press cut"(straight down cut). Finally, a squash is a bad tester because it's mostly the vacuum sucking on the side of the blade that costs force to cut it. Try a tomato or onion? Jun 17 '20 at 4:14
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    I gave up on ever trying to get it right - cooking.stackexchange.com/a/108740/42066 ;)
    – unlisted
    Jun 17 '20 at 8:52
  • @AMtwo Thanks. I'll ask my grandpa to film his sharpening and upload it here later.
    – NNOX Apps
    Jun 17 '20 at 20:14
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This is like saying "I bought my grandpa a Faber Castel pencil and 200 gm acid-free paper, and now the pencil is not drawing realistic portraits, why".

Knife sharpening is a fine motor skill. The only way to learn it is through hours of deliberate practice. It is also a tricky skill to learn, because you don't really get immediate feedback per stroke, and there is not that much affordance. So it is more difficult to learn, especially learn on your own, than something like throwing a ball.

If your grandpa wants to sharpen his knives with a stone, he will have to put in his hours of learning. It is impossible to say how many he needs before he starts to see consistently good results, it can be a dozen or it can be over a hundred.

It is best to start learning on old, bad knives, since a learner's first attempts frequently destroy the edge, making it more difficult to repair it later.

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