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mdoublestack
06-19-2012, 05:08 AM
Late night sharpening, I am thinning my 240mm mizuno gyuto... mostly for fun, and to take some metal off behind the edge, and make it a better cutter. It is taking a VERY long time, so it got me thinking... do you go thin all the way to the edge, making one large(+/-.5") bevel, deburr, then microbevel? Or do you just thin it as long as you feel like it then establish another "primary" bevel? Ive done both in the past, just not on this knife. Blue #1 is resilent. Sheesh

Benuser
06-19-2012, 06:49 AM
On asymmetric monosteel J-knives I want the left to stay as flat as possible. I thin the right, convex side with coarse sandpaper at the lowest angle I feel comfortable with - a few degree. Make sure the scratches don't reach the edge. I use sandpaper in the P120-600 range.
With cladded blades you will have to remove some soft clad steel, probably on both sides, try with P600.
Sandpaper works very fast. You're creating a huge convex relief bevel which blends with the blade's geometry. I therefore can't say in general how large that bevel is, but I guess some .5" is very likely.

Benuser
06-19-2012, 07:57 AM
If you want to get rid of the existing edge (e.g. with a new knife) go till you raised a burr. Make sure not to do that with your coarsest paper or stone. I would prefer though to vary the thinning angle somewhat to respect the convex geometry. You aren't looking for two flat sides which would cause wedging.

tk59
06-19-2012, 08:17 AM
+1. For a clad knife you'll have to thin both sides to keep the cladding even. I thin until I establish a new edge and then add a microbevel. I do thinning on Gesshin 400 or Beston 500.

mdoublestack
06-19-2012, 08:36 AM
Thanks guys. I am using the beston 500. It is relatively even on both sides, but i still have not established a "new edge" If were to change the angle, make it more obtuse to create a new edge, would that help convex the edge, if I were to blend it later on. Or should I continue as you say, until I establish a new edge, with the very acute angled wide bevel, then micro bevel.

Thinning is a wild, tedious process

Benuser
06-19-2012, 09:57 AM
I would stay with the blade's geometry. Have you thinned both sides?

Andrew H
06-19-2012, 10:26 AM
I thin from around .75" of the blade down to just before the edge, no burr formation. Then I grind in a new primary edge.

mdoublestack
06-19-2012, 03:09 PM
This is where I am at right now in my thinning. Thinned on both sides, about .75" At this point, would you grind another bevel(primary edge) then a micro bevel - this would completely convex the blade, no? That is where my intuition is leading me. Conversely, if i continue to thin until I have one large bevel, with burr, then micro bevel, it would be more of a flatter grind throughout most of the blade, right? Would that encourage food to stick?



I thin from around .75" of the blade down to just before the edge, no burr formation. Then I grind in a new primary edge.

Eamon Burke
06-19-2012, 03:29 PM
Keep in mind that if you are thinning by creating your own bevels, I.E. not following the existing grind the maker put there, you are altering the knife in a drastic, fundamental way. If you change the bevels that were originally ground into the face of the blade, make no mistake, you are making a different knife.
hic sunt dracones

NO ChoP!
06-19-2012, 03:47 PM
Well, I've changed every bevel on every knife I've ever owned, and have always been 100% pleased with the result; new edge outperforming factory by a long shot.....


That being said, you can thin behind the edge, and still return the factory set bevel; as pointed out above; which would be highly advises, since the thinning angle may be overly acute.

mdoublestack
06-19-2012, 03:57 PM
I understand this, but I am following the existing grind, for the most part... Mizunos have a large secondary bevel. Just over time, almost two years(thinned only a several times, and sharpened the edge many, the secondary edge is not pronounced. I noticed it is not the cutter it used to be, so I am thinning. here are a couple photos

http://farm8.staticflickr.com/7219/7403340306_157cfff1c6.jpg (http://www.flickr.com/photos/80750318@N03/7403340306/)
Mizuno (http://www.flickr.com/photos/80750318@N03/7403340306/) by mdoublestack (http://www.flickr.com/people/80750318@N03/), on Flickr
http://farm8.staticflickr.com/7235/7403339260_6dbc9d04de.jpg (http://www.flickr.com/photos/80750318@N03/7403339260/)
My Mizuno (http://www.flickr.com/photos/80750318@N03/7403339260/) by mdoublestack (http://www.flickr.com/people/80750318@N03/), on Flickr



Keep in mind that if you are thinning by creating your own bevels, I.E. not following the existing grind the maker put there, you are altering the knife in a drastic, fundamental way. If you change the bevels that were originally ground into the face of the blade, make no mistake, you are making a different knife.
hic sunt dracones

Eamon Burke
06-19-2012, 04:34 PM
A knife like that can and should be thinned every time, the shoulder should still match the edge profile and the blade road should be the same height.

NO ChoP!
06-19-2012, 04:37 PM
Nice looking knife, BTW....

mdoublestack
06-19-2012, 04:43 PM
When you say thinned, do you mean to the edge? as in, one large bevel, then micro bevel it? This is my quandary and why I am at a stand still, as i have thinned it greatly, but I am still not at the edge.


A knife like that can and should be thinned every time, the shoulder should still match the edge profile and the blade road should be the same height.

ThEoRy
06-19-2012, 05:15 PM
You should sharpen that knife every time by grinding the blade road just like you would a single bevel knife.

Eamon Burke
06-19-2012, 05:52 PM
Has Jon made a video on hamaguri edges?

The jki vids would be a big help for your project.

mpukas
06-19-2012, 06:03 PM
Knives like your Mizuno that have a large secondary bevel and a distinct shinogi line should be sharpened just as you would a single bevel knife, but on both sides, IMHO. They essentially have a hamaguri edge on each side. The secondary bevel is sharpened first, from the shinogi line down to roughly the lamination line. The primary bevel is then sharpened from the lamination line to the edge.

The secondary bevel is sharpened first. The secondary bevel does not reach the edge. It's up to you what grits and finish you use - you can just use a course stone and be done with it, or you can use a progression for a finer finish.

I agree that knives with large secondary bevels like this should be "thinned" every time they are sharpened, meaning both bevels should be ground at each session. It's why your knife has become not as good of a cutter as it once was.

It's interesting to me that when talking about a single bevel knife, thinning is never mentioned - both bevels are ground each time the knife is sharpened.

JBroida
06-19-2012, 06:28 PM
Has Jon made a video on hamaguri edges?

The jki vids would be a big help for your project.

there's some stuff about hamaguri edges in my single bevel videos... the concepts are roughly the same.