Usuaba grind w radius platen

Brock Cutlery

Brock Cutlery

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Jan 10, 2015
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I am working up a couple of Usuba knives, my first attempt at these.
I'm interested to hear what others with experience either using or making this style.

The blanks are 4.5mm roughly, so very thick. I have used Nathan's 36" radius platen to put in the ura and even on the blade bevel.
I'm not sure I want to continue with it on the bevel, I still have about 1/8th to play with so can easily just take it back flat. My thought about using the radius grind here is that it could be significantly easier to sharpen, for a while...
I really like the ura shape produced by the platen. It's pretty cool and relatively easy to work with. The only other ura's I've done are on several Yanagi blades. Those were done on my 14" wheel, which worked well on the shorter height on these blades. It would be far too deep on this Usuba at 46mm.

So I'm just looking for some thoughts if anyone has a mind to discuss.
Thanks all

36RadiusPlaten.jpg


UsubaGrind-4.jpg


UsubaGrind-5.jpg


UsubaGrind-6.jpg
 
I use the radius platen for doing the urasuki. I don't like a hollow ground omote bevel, so I use a flat platen there. When all grinding and basic shaping is done to 400 grit, I flat lap the ura to get a slight flat area along the ha ( about 2mm wide). This assures the front bevel is super sharp. From there I go to the final sanding and sharpening, giving the ura one last lap with paste on a leather stropping board to remove any burr.
 
I appreciate your input Stacy. I'll cut that bevel flat and call it good. That is sound advice.
 
So would the 36 inch platen be too "shallow" for a yanagiba? I have a 36 and a 72.
 
I'm not sure about that. It is def much more shallow than the 14 wheel.
One of the challenges I have on a yanagi even with the 14 is when I use a 400 stone, it will scratch inside the ura. Just the loose grit.
The 36 would exacerbate this, but you could just get the flat on the ura done on the grinder, then go to 1000 stone or so.
That's the best answer I have for ya, fwiw. :)
 
I use the 72" most of the time. Urasuki does not need to be deep.

On a 36" wheel, the depth of a 1.5" wide Urasuki is .0015". It is .00075" deep on a 72" wheel.

On a 14" wheel, the hollow is .04" deep .... and that is pretty close to coming out on the other side unless the blade is quite thick. Fine for a deba, but on an usuba that is only .06" thick at the spine, that is cutting it pretty close. Probably OK for a Yanagi-ba, but still deeper than needed.

To avoid grit scratching, rinse the stone and blade frequently, as well as using lots of water lubricant while stoning.

Trick for sanding out any hollow grind:
To make an inside sanding mandrel for sanding Urasuki and other hollow grinds, this works great.

Take a piece of 2X4 that is 1" shorter than the wheel radius being sanded ( 35 for a 72, 17, for a 36, etc.). Attach a 2X4X 1" thick block of the hardwood that you will be using for the sanding backer to it with a few drops of CA glue.

Stand at the grinder with the block and arm held level at the center of the wheel or platen. Place the end of the wooden arm against you chest, and holding the block end with both hands sweep the block up and down across the wheel/platen (obviously, held horizontally). The block will grind in a curve that matches the distance from the pivot (the end on your chest) to the grinder wheel/platen. Pop the block off the 2X4 and mark the back of the block to know what size hollow it matches ( woodburning it in is best way). You can easily make a set of 12, 16, 24, 36, and 72 inch blocks in half an hour (match them to the wheels and radius platens you use or plan to get). Tip- start with the largest, and cut down the arm length for each subsequent sizes. This set will sand out any hollow you do.

Second tip:
Search for hanging parallelogram grinding ( Salem Straub uses it and wet grinding for almost everything) and see how simple it is to get dead perfect hollows every time. (works for flats, too). Two screw eyes in the ceiling, some light chain, a bar or pipe of steel/aluminum, and a magnet or clamp on the end for the blade .... that's it.
 
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Stacy E. Apelt - Bladesmith said:
I use the 72" most of the time. Urasuki does not need to be deep.

On a 36" wheel, the depth of a 1.5" wide Urasuki is .0015". It is .00075" deep on a 72" wheel.

On a 14" wheel, the hollow is .04" deep .... and that is pretty close to coming out on the other side unless the blade is quite thick. Fine for a deba, but on an usuba that is only .06" thick at the spine, that is cutting it pretty close. Probably OK for a Yanagi-ba, but still deeper than needed.

To avoid grit scratching, rinse the stone and blade frequently, as well as using lots of water lubricant while stoning.

Trick for sanding out any hollow grind:
To make an inside sanding mandrel for sanding Urasuki and other hollow grinds, this works great.

Take a piece of 2X4 that is 1" shorter than the wheel radius being sanded ( 35 for a 72, 17, for a 36, etc.). Attach a 2X4X 1" thick block of the hardwood that you will be using for the sanding backer to it with a few drops of CA glue.

Stand at the grinder with the block and arm held level at the center of the wheel or platen. Place the end of the wooden arm against you chest, and holding the block end with both hands sweep the block up and down across the wheel/platen (obviously, held horizontally). The block will grind in a curve that matches the distance from the pivot (the end on your chest) to the grinder wheel/platen. Pop the block off the 2X4 and mark the back of the block to know what size hollow it matches ( woodburning it in is best way). You can easily make a set of 12, 16, 24, 36, and 72 inch blocks in half an hour (match them to the wheels and radius platens you use or plan to get). Tip- start with the largest, and cut down the arm length for each subsequent sizes. This set will sand out any hollow you do.

Second tip:
Search for hanging parallelogram grinding ( Salem Straub uses it and wet grinding for almost everything) and see how simple it is to get dead perfect hollows every time. (works for flats, too). Two screw eyes in the ceiling, some light chain, a bar or pipe of steel/aluminum, and a magnet or clamp on the end for the blade .... that's it.
Click to expand...

Your post is just chock full of info Stacy. :)

I have a couple of questions if you will.
.00075 seems very shallow. How many sharpenings will it take to wear that to flat? Any idea?

You mention .06 for an usuba. I am seeing far thicker. .06 is 1.5mm.
3.5 mm seems pretty common for a traditional usuba. I went to 4.5 on mine, and probably went too thick. I might take that down to 3.5.
.06 seems almost nakiri-like.
Here are some specs on a Shig usuba:
Chin to tip length - 155mm
Blade height at chin - 45mm
Width of spine at handle - 5.1mm
Width of spine above chin - 4.2mm
Width of spine at middle - 3mm
Width of spine 1cm from the tip - 2.2mm

I had forgotten about the parallel grinding technique. That is probably worth trying out.

Thanks!
 
I know you asked Stacy, and I'm sure he'll explain in depth, but in general when a user is sharpening a traditional single bevel, the ura side is just used to deburr. That's why it doesn't need to be deeply concave. The bevel finish is also easier to keep consistent by the user when the front bevel is as consistently flat as possible, although if using natural stones or other good slurry producing sharpening stone, the slurry can get into the slight deviations from flat.

I bet most traditional Japanese sharpeners use something smaller than a 72" waterstone wheel to make the ura though.
 
True, most kaiten toshi are around 36" wheels. A really big one is 48". Small shops may have a 24" wheel. The ones in the Osaka factories were usually 24" to 30".
In the old Sheffield factories there were a few 60" wheels, but most were in the 24-36" range.

Here is a great image of a Japanese factory worker at the wheel:
https://www.bing.com/images/search?...608053438206444716&selectedIndex=0&ajaxhist=0



I was mainly posting grind depth info more than specific blade type thicknesses.

I like an usuba to be thinner than most import versions. To me, usuba that are thick seem heavy and lack finesse in the hand.

Most I have seen are 3.5 to 4mm thick ... or thinner. The import blades are also a bit longer than I like. I feel a 100-125mm/4-5" blade is just right for the tasks it will perform. For larger veggie tasks, a nikiri is what I would recommend.

The shape and size I make is basically the Kamagata Kurimuki style

To me, an usuba is a paring/utility knife. It peels cucumbers, dices garlic, chops scallions, and picks them up to drop in a pan or bowl. It will trim the silver skin of a fillet, cut the tail off a perch, as well as cut up a chicken breast for a stir-fry. It is sort of a blend of santoku and a nikiri. I make most in 3mm laminated steel, but the ones in very thin mono-steel ( 1.5 to 2.5mm / .06 to .09") are also quite popular. I use CPM-S35VN or Hitachi white steel for those. I like to round down from the nose for the first inch, and then go straight back to the heel with no rocker. The thicker blades I do in single grind with urasuki, and the thin ones double grind.
 
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I have not made a knife with an Ura but have sharpened a lot. Ura is not meant to bw heavily sharpened. Once the knife is finished the ura shouldnt ever hit a coarse stone again imo if maintained properly. Also the way i was taught woth Urasuki sharpening is apply pressure only on forward strokes. I will sharpen jigane/hagane on coarse stones and not touch the ura until ive progressed finer. I will take Ura to something coarser if its a cheap knife and ura wasnt ground evenly, but that is about it.
 
If one was to get a curved platen for grinding urasaki, which "size" would you guys recommend to be most versatile? 36, 48 or 72?
 
comet_sharp said:
I have not made a knife with an Ura but have sharpened a lot. Ura is not meant to bw heavily sharpened. Once the knife is finished the ura shouldnt ever hit a coarse stone again imo if maintained properly. Also the way i was taught woth Urasuki sharpening is apply pressure only on forward strokes. I will sharpen jigane/hagane on coarse stones and not touch the ura until ive progressed finer. I will take Ura to something coarser if its a cheap knife and ura wasnt ground evenly, but that is about it.
Click to expand...

One of the sharpening videos I watched suggested that the blade is so think it will bend slightly on sharpening. So alternating keeps it straight and allows sharpening. If it bends away from the stone it won't sharpen. That's what I gathered, and I can say I had trouble on my first Yanagi... But I don't have much experience in this.
 
This is the finished grind on the ura at 36" radius and 800 grit. As Stacy indicated, I think this is the radius sweet spot, at least for this one, which is 45.5mm tall.
Other opinions most welcome though. What am I not seeing? :)

grindfinished2a.jpg
 
Looks good. I have a 36 and 72, but I typically use them to get clean symetrical clip grinds on bowies and such. I grind in the curve of the clip and then roll the blade over to the appropriated angle for the swedges. I have only ground one knife with them, a small 1/8 thick CPM 3V hunter using the 36 and I liked how it turned out.
Brock Cutlery said:
This is the finished grind on the ura at 36" radius and 800 grit. As Stacy indicated, I think this is the radius sweet spot, at least for this one, which is 45.5mm tall.
Other opinions most welcome though. What am I not seeing? :)

grindfinished2a.jpg
Click to expand...
 
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