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 Post subject: Thinning knife
PostPosted: Mon Sep 16, 2013 7:12 pm 

Joined: Tue Mar 05, 2013 1:47 pm
Posts: 74
Location: Oslo Norway
Hello
Yesterday I tried to thin a knife for my first time, but I do not feel that I succeed very well.

The mac knife have a very defined secondary bevel. I started to thin by pressing behind the secondary edge as Murray Carter says.
But I the resulting pattern did not look very nice:
File comment: Mac knife
thinning.jpg [23.19 KiB]
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I used a Bester 500

1. I seem like that there are a very uneven removal of metal and that metal is only removed at some spots. Is it possible to got a more even pattern.
Will this become better if I remove more metal?

2. How much should I thin at each thinning.

3. Is it best to count passes on each side in order to

4. Should I thin by pressing on the secondary bevel as Murray Carter says or should I thin by holding the knife at very low angle?



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 Post subject: Re: Thinning knife
PostPosted: Mon Sep 16, 2013 8:22 pm 

Joined: Fri Aug 03, 2012 10:01 pm
Posts: 205
First of all, don't get discouraged, it's all part of the learning curve. Since you are leaning, don't worry about scratches, as they can tell you alot about your technique if you take the time to really diagnose it.

One observation for you, it appears that you are hitting the blade stock above what would be considered the shinogi line, above the secondary bevel. If you slow down and really observe your work after a few strokes, there's really no reason to be scratching the steel above the shinogi. Slow down, make a few strokes on the stone and really take the time to observe where your hitting. Placing your finger pressure on the opposite side of the area you want to grind is correct. You could also practice by using something above 500 grit, like 1K+, something that will show you scratches but not remove as much steel. Then when you feel confident with your movement and pressure, drop down to lower grits and grind away.

As Carter points out, it's a bit of an experimentation process to learn the most effective secondary blade geometry for your own uses. He uses the old machinist trick by lightly squeezing the blade between your thumb and index finger and SLOWLY running your fingers from the blade spine all the way down to the primary edge. With practice it gives you some mental imagery of how thick your blade is and how much more you want to thin it out.

In my experience, especially with some new knives that have not been thinned, you will find high and low spots in your secondary bevel that will take time to even out after multiple sharpening sessions. Also check to see if the blade is perfectly straight, or at least reasonably so.

Josh


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 Post subject: Re: Thinning knife
PostPosted: Tue Sep 17, 2013 6:55 am 

Joined: Tue Mar 05, 2013 1:47 pm
Posts: 74
Location: Oslo Norway
I have a lot of german style knives without a very defined secondary bevel.

1.How large an area should I thin. Is the area I have outlined in the figure large enough?

File comment: Thi
thinning.png [3.13 KiB]
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2.I find it very difficult to get the boarder between the secondary bevel and the rest of the line to be a straight line. Any tip?

3.Should I thin by laying the knife flat on the stone and pressing on the knife in the area I want to thin or should I raise the knife and thin with an low angle



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 Post subject: Re: Thinning knife
PostPosted: Tue Sep 17, 2013 8:18 am 
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Joined: Wed May 16, 2012 4:42 pm
Posts: 3656
Location: USA... mostly.
NORWAY <> 1a: As Josh mentions, blade roads are commonly uneven, and as you grind away over time you will flatten them out.

2a: How much you thin is personal preference. You should notice the difference in sharpening your final bevel once thinned behind it, and then you will see how that translates in performance on the board for you.

3a: That depends on your feel. Counting strokes with equal pressure dictates your even removal of metal on both sides which retains OEM bevel symmetry/asymmetry. If you can eye it, counting is not necessary, but usually recommended.

4a: On a knife with a clear "secondary bevel", I lay the bevel flat on the stone, and depress right below the Shinogi on the back side as I am grinding. On a knife like a Wusthof, I thin by effectively sharpening at an extremely acute angle to thin behind the edge, and then I come back to put my final bevel on that thinned area.

1b: Refer to 2a's & 4a's answer.

2b: Slow down. Consistent angles, pressure, and orientation produce consistent and defined scratch patterns.

3b: Refer to 4a's answer.



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 Post subject: Re: Thinning knife
PostPosted: Tue Sep 17, 2013 9:05 am 

Joined: Tue Mar 05, 2013 1:47 pm
Posts: 74
Location: Oslo Norway
Thank you for answers.
I am pleased with my primary edge sharpening, but I have found thinning much more difficult since I do not have any objective way of judging the results. On the primary edge I have both the burr and the actual sharpness.
But I will then try to count strokes since I do not have the feel for it yet.



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 Post subject: Re: Thinning knife
PostPosted: Tue Sep 17, 2013 3:32 pm 

Joined: Wed May 16, 2012 1:49 am
Posts: 304
Location: Amstelveen, The Netherlands
Have a micrometer to get an idea of what you're doing and what you're aiming at.


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 Post subject: Re: Thinning knife
PostPosted: Tue Sep 17, 2013 3:48 pm 

Joined: Tue Mar 05, 2013 1:47 pm
Posts: 74
Location: Oslo Norway
No. Is that something I need? I plan to do some practice on some cheap norwegian 30$ german style knives (soft hr 56)



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 Post subject: Re: Thinning knife
PostPosted: Tue Sep 17, 2013 5:23 pm 

Joined: Wed May 16, 2012 1:49 am
Posts: 304
Location: Amstelveen, The Netherlands
Get one. Isn't too expensive -- some €25 for a basic one IIRC -- and very helpful in understanding blades' geometry.


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 Post subject: Re: Thinning knife
PostPosted: Tue Sep 17, 2013 6:56 pm 
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Joined: Thu Nov 22, 2012 4:17 am
Posts: 4044
Location: Kentucky
If you don't like the looks of your knife after thinning you can get some finger stones from Mark to even out and blend the scratch marks on the knife for a better appearance. You can used them to put a mirror polish on it if you wanted.



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 Post subject: Re: Thinning knife
PostPosted: Tue Sep 17, 2013 7:44 pm 

Joined: Tue Mar 05, 2013 1:47 pm
Posts: 74
Location: Oslo Norway
How do you thin your knife which have no clear secondary bevel as japanese knives has. The thickness of these knives often decreases gradually towards the edge (often in a convex way). Do you try to thin the whole blade, or only a part of the blade above the primary edge.

Is it possible to use water stone to grind the whole blade area? Have some plan of thinning down my Artifex. But is it possible to do this for hand?



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