This review consists of :
Washboard sharpening system :
Washboard sharpening plate - approx 2"x 8" x 1"
Handmade wooden base
4 color illustrated user's guide
Slug of custom formulated Silicon Carbide honing compound - approx 4k JIS -
Sheet of 320 grit wet/dry silicon carbide sandpaper - cut to fit
Sheet of 600 grit wet/dry silicon carbide sandpaper - cut to fit
Sheet of 120 grit wet/dry silicon carbide sandpaper - cut to fit
Artist eraser for maintaining the sandpaper in use
As a quick and rough trial to get some data to be able to design sensible experiments, the Washboard was used with 80 grit, open coat, aluminum oxide sandpaper to reset the main bevel on an Elmax folder. A picture of the sandpaper is shown to the right under 50X magnification (the picture shows an image of true width equal to one millimeter).
Approximately 10 lbs was used as the load/sharpening force which produces a pressure on the sandpaper between 5 and 10 psi depending on the contact area which varies along the knife. The beveling was repeated 59 times.
As a few interesting notes :
In regards to the curvature, note in the picture on the right, that strip of black is what is left after a flat stone was used to grind the knife and apply a straight/flat bevel at a constant angle. The benchstone (Bester 700) could not make contact on that section of knife (the black strip along the edge) showing it had a vastly increased angle.
Even though the Washboard is a rigid backing, the sandpaper itself is compressible and this flexing of the paper is what makes the curvature on the blade grinding. Note that this is a known feature/ability of sandpaper which makes sandpaper in general give a more consistent finish than fixed abrasives. As the abrasive grits in general are uneven in any abrasive, the ability of the sandpaper to compress under the large/high points of the bigger abrasives allow it to present a more uniform effective abrasive size.
In general it also isn't a strict downside that a convex or curved bevel is formed, it just has to be taken into account in the sharpening.
For a second comparison, the Washboard was compared against a small piece of pine wood which was much more narrow and would give similar contact pressure under the same force as the textured surface on the Washboard. The knives shown to the right were chosen at random and sharpened with either the Washboard or the simple Pine backing. The sandpaper used was 400 grit Norton Adalox which was placed on two sheets of paper as the maker/designer had commented about using multiple sheets to change the "feedback". The force used was under a pound and since it was being applied to narrow edge bevels it produced a very similar pressure as to the first comparison, 5 to 10 psi.
In short :
The reason that the sandpaper sharpened so much faster than the Benchstone is that as it applies a convex bevel it simply is increasing the angle and thus forming an apex rapidly. This of course isn't a sustainable practice. The next time the knife is sharpened this doesn't happen. However it can explain the very strong initial reaction that people often have to sandpaper sharpening as the first time it is used it has that very fast response. Of course the same can be achieved on a benchstone by simply increasing the sharpening angle. But again, this isn't a sustainable/practical approach as it leads to rapid loss of cutting ability and general performance though thickening of the bevels.
To confirm that this behavior was not due to the multiple sheets, they were stripped off and only one sheet was used and a ZDP-189 Delica was sharpened with the same sandpaper and the Washboard almost immediately apexed the bevel by again adding an increased curvature to it and increasing the angle of the bevel.
The Washboard was now used with one of the sheets it came with, 600 grit Gator which is a silicon carbide abrasive. Silicon carbide is a slightly harder, slightly sharper and a more friable abrasive than aluminum oxide. The knife used as a SM-100 kitchen knife by cKc knives. The Washboard was again compared to just using a Pine block. In this case not only the sharpness was compared but also the edge retention.
With the knife sharpened it was used to slice 1/8" cardboard on a 2" draw and the TCE statistic used to determine the edge retention (cutting down to 1.5% of optimal sharpness). The sharpness was measured by cutting Espirit spinning thread under a 50 gram load. The results, as shown in the graph on the right are interesting. The apex was not cut off to remove any strained/weakened metal during the cutting to check if the sandpaper alone would do that in the course of regular sharpening.
In short :
In regards to the loss of edge retention with repeated sharpening this is simply the build up of damaged steel at the apex which isn't fully removed by the sharpening. In general an abrasive as coarse as this should be able to freshly reset the edge however due to the compression of the sandpaper and how it increases the apex angle, it tends to form the apex before the damaged steel is removed.
In regards to the superior edge retention of the Washboard, in retrospect, this experiment was a little biased because all of the runs with the Pine were done and then all the runs with the Washboard were done, they were not staggered. The knife had been heavily used before the Pine trials and thus the edge could have been left with strained metal at the edge which compromised the performance.
A forth trial was very similar to the third with the switches :
In short there is no significant difference in either :
between using the Pine and Washboard. As expected, the difference in the last run with the 600 Gator was most likely just due to the initial starting condition not being equal between the two sharpening methods.
The fifth trial was using the Washboard to sharpen a simple stainless steel knife and doing repeated edge retention trials slicing cardboard. As noted in the graph on the right, with each trial :
The reason for this behavior is that the weakened metal at the edge isn't fully removed and thus the apex keeps forming on weakened metal. This is why in general in order to keep optimal sharpness and edge retention it is often useful to cut the apex back slightly to remove any strained/damaged/worn steel before sharpening.
In short, no significant difference could be seen between using the Washboard and a simple piece of Pine as a support. A few general observations :
Note the maker of this system objected strongly to the work done with the Washboard, however the arguments made in general tend to be based on a severe misunderstanding of even basic issues in sharpening such as :
I am amazed the paper can tolerate 10 lbs of grinding without clogging up and the grinding slowing to a crawl in very short order. Then again, I've never pressed that hard while sharpening with it. Usually in the nature of 3-8 ozs and twice that when initially stropping.
When grinding, the critical parameter isn't the force as the maker constantly stresses (see the thread below), it is the pressure produced by the force. This is obvious if a point of a knife for example is ground against a stone. As the contact area is very small the pressure becomes very high so the tip will grind very rapidly even at a low force as again the grinding speed is a function of the pressure. This is also why much more force has to be used to cut with a very wide file vs a very narrow one, again it is the pressure that is critical in the cutting speed/action.
In the case of the grinding on the Elmax knife, as it was grinding in the main blade bevel which was very wide, even though the force was high, as noted in the above the pressure was very low. The pressure was in fact in the range of the pressures which would be produced by the force the maker notes they use when grinding edge bevels.
Note as well that the maker tended to severely criticize other sharpening systems which are well known and extensively used and the criticisms are simply non-valid at at times simply insensible. As well, any criticism of the Washboard is met with extreme demands for testing methods but praise is cited for which no such demands were requested. It clearly showed a lack of desire for obtain an unbiased result and a simple search for praise.
Comments can be emailed to T0.1 M
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