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 Post subject: Magical Physics of the Trailing Stroke?
PostPosted: Wed Jun 27, 2012 3:30 pm 

Joined: Wed May 16, 2012 11:12 am
Posts: 61
So, I have noticed that when freehand sharpening, I get huge benefits from the trailing stroke of a blade across the stone. In some cases I will find that by just using backwards trailing strokes (e.g., rather than pushing the blade forward on the stone, I pull it backwards with the edge to the stone) the blade edge become very precise and crisp. I used to finish my sharpening session with a few trailing strokes and so could see the benefit of removing a burr, etc; Now I find that by upping the amount of trailing strokes, the edges are just plain better than by using mostly forward strokes. The question I have, is why? Is there some benefit to the trailing stroke that cannot be achieved as efficiently by the forward stroke? The only thing I can surmise is that the trailing stroke allows the sharpener to hold the angle of the blade to the stone more consistently. It almost feels as if the blade angle “locks in” to the stone and holds its angle as the blade moves in reverse, with less movement in the heal which thus creates a more consistently-held angle. I don’t know if that is truly the reason for the better edges, but would really like to understand better the physics of the trailing stroke. Arcane, yes? But it really does work. Sharpening wizards, what's up here?


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 Post subject: Re: Magical Physics of the Trailing Stroke?
PostPosted: Wed Jun 27, 2012 3:50 pm 
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Hi Chester,

I've found the same thing and this is why stropping provides such a big benefit when you finish your knives. Here's my theory. Leading strokes are aggressive and many finer stones tend to be soft. This is a bad combination since I've experienced what I call snow plowing where the edge doesn't gouge the stone so much as it plows into the stone and rolls the edge. When people tell me they get their knives sharp on a 1-3 K stone but then they move to a 5-8K stone and the edge get's duller that is what I usually suspect. If you're dealing with a softer, higher grit stone, using trailing strokes (stropping) should avoid the snow plow effect. At least that's my theory and it works for me.

Can you sharpen using only trailing strokes? Yes you can. However, it will take you a lot longer and I usually see no real benefit on lower grit stones.

A common and effective routine I use is:

500 using both leading and trailing
1K using both leading and trailing.
Deburr (Either with a felt block or using trailing strokes on the 1K)
5K trailing strokes only
Strop with CO Paste on Balsa or leather

I can usually get most knives hair popping sharp with this method and that's good enough for me.



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Mark Richmond
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 Post subject: Re: Magical Physics of the Trailing Stroke?
PostPosted: Wed Jun 27, 2012 4:05 pm 

Joined: Wed May 16, 2012 11:12 am
Posts: 61
Good to see that it is not just me that has made this observation (hey, even a blind squirrel ocassionally finds a nut). I have indeed noticed that on occasion I will lose progress when sharpening (e.g., the knife actually gets duller as I sharpen) but when this occurs, it is only after forward strokes. Again, my theory is that the forward motion is doing exactly what you are describing, which is a form of snow plowing into the stone which is trashing the edge. While I guess it is possible that this can also occur on the reverse stroke, it seems so much easier to hold that angle against the stone moving from the front to the back. Also, to the extent that the angle to the stone is changing, the affect on the blade must be much greater while pushing foward than in reverse. Interesting that you too increase your trailing strokes at you move higher in grits. Wish I stumbled on this trick years ago!


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 Post subject: Re: Magical Physics of the Trailing Stroke?
PostPosted: Thu Jun 28, 2012 1:54 am 
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Posts: 473
Yep, it's easier to not overshoot the edge angle and it keeps the abrasives from being pushed into the converging planes that make up your edge, resulting in deformation.

Sometimes this is desirable, like using coticule stones(with their round-ish Garnet abrasive particles) on straight razors to prevent "over-honing" or creating an edge that is too laser-like and therefore more likely to shave off tiny layers of skin, leading to irritation.

But for kitchen knives, it's a whole new thing. It's why I think the old idea that a kitchen knife needs 2 stones(coarse and fine) is not as good as having a stone and strop(medium grit stone, with a loaded strop).



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 Post subject: Re: Magical Physics of the Trailing Stroke?
PostPosted: Thu Jun 28, 2012 3:09 pm 

Joined: Fri May 25, 2012 12:17 am
Posts: 7
"A common and effective routine I use is:

500 using both leading and trailing
1K using both leading and trailing.
Deburr (Either with a felt block or using trailing strokes on the 1K)
5K trailing strokes only
Strop with CO Paste on Balsa or leather

I can usually get most knives hair popping sharp with this method and that's good enough for me."
[/quote]
++++++++++++++++++++++++++++++++++++



Mark, What is CO paste? Thanks..


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 Post subject: Re: Magical Physics of the Trailing Stroke?
PostPosted: Thu Jun 28, 2012 3:14 pm 
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Location: Herentals, Belgium
Chromium Oxide:

http://www.chefknivestogo.com/choxd4oz.html



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Michiel Vanhoudt

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 Post subject: Re: Magical Physics of the Trailing Stroke?
PostPosted: Thu Jun 28, 2012 3:56 pm 
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It should also be noted that in traditional Japanese knife sharpening routines, you only put much pressure on edge-leading strokes to deburr.



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 Post subject: Re: Magical Physics of the Trailing Stroke?
PostPosted: Thu Jun 28, 2012 4:31 pm 
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Location: Madison Wisconsin
hugo wrote:"A common and effective routine I use is:

500 using both leading and trailing
1K using both leading and trailing.
Deburr (Either with a felt block or using trailing strokes on the 1K)
5K trailing strokes only
Strop with CO Paste on Balsa or leather

I can usually get most knives hair popping sharp with this method and that's good enough for me."

++++++++++++++++++++++++++++++++++++



Mark, What is CO paste? Thanks..[/quote]

Hi Hugo,

Sorry about that. I use Chromium Oxide paste on a strop (usually balsa).

This is the paste:
http://www.chefknivestogo.com/choxd4oz.html

This is the balsa:
http://www.chefknivestogo.com/bamapa.html

There's a video on the balsa page that Shaun did that will show you the technique for anyone that reads this and doesn't know what stropping is. It's just using edge trailing stroks.



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 Post subject: Re: Magical Physics of the Trailing Stroke?
PostPosted: Thu Jun 28, 2012 4:54 pm 

Joined: Sun Jun 10, 2012 1:17 am
Posts: 355
so i should trail using my 6000grit? i always go leading and trailing through out all the stones. but sometimes i do dig in and try to lap it off.


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 Post subject: Re: Magical Physics of the Trailing Stroke?
PostPosted: Thu Jun 28, 2012 6:09 pm 
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You can do both, but I think you should finish the time you spend on every stone with exclusively edge-trailing strokes to ensure you are getting the stone's full finish.



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