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In this video, I introduce the Nubatama Ume 120 grit stone, showing my first impressions of this stone. This stone should be a very fast cutter (it is) and I will demonstrate how it performs by setting a new bevel on a demonstrator Kershaw pocket knife that has absolutely no edge at all. I demonstrate the total absence of an edge by showing how the knife doesn't cut by running the edge across my palm with some force.
I'll also discuss burr formation and initial establishment of a bevel..
I begin by soaking the stone under a running tap for a couple minutes. It isn't necessary to do this for a long time as the water will drain after a while anyhow. For a coarse stone, it saturates pretty quickly to a usable state.
Adding water as I begin to abrade it, I very rapidly establish a bevel. I discuss why you would optimally NOT grind on just one side to establish a burr, but rather work on one side and then the other. I also point out that on a new knife there is no possibility of preexisting fatigued metal. Also the size of the bevel is not angle dependent but rather on the amount of time spent at each point along the edge determining bevel width at that point. This is discussed in more detail in my Advanced Sharpening video discussing blade asymmetry.
So in very short order, I establish an edge. I also demonstrate burr removal using a lateral stroke with light pressure along the full length of the blade, rather than relying on wine corks, felt, wood and other techniques that rip off rather than abrade the burr. Light pressure minimizes burr formation. Put another way, increased pressure results in larger burrs.
Edge testing with a rolled up paper towel demonstrates an excellent toothy edge produced in record time. I also sharpen the tip of the knife demonstrating tip repair technique. I do a few more strokes after sharpening the tip to remove burr associated with tip metal removal that gets on to the two sides of the knife.
The stone doesn't load up at all. It does show some stone wear when used for heavy grinding (more that say the 150 Nubatama Bamboo), but removes metal more rapidly. Because it removes metal so fast, the wear for this application isn't a major concern. Reapplying the mud to the stone is to your advantage and if the stone is more saturated, the mud need not be rinsed off the stone when adding water to the stone as I did several times.. I would recommend flattening after performing a bevel setting procedure using either the Atoma 140 , DMT XXC or another even coarser stone such as the Nubatama Aratae.
This stone should be an Excellent stone for initial bevel setting, cleaning up scratches from Atoma 140 or DMT XXC diamond plate scratches The level of finish of the stone is quite nice for such a coarse stone, easily comparable to other stones of even finer grit in the range of 200 to 400 grit. Depending on the knife one could follow this stone with a high quality 1000 grit stone quite nicely.
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