Couple of other thoughts on sandpaper sharpening in general.
They come in weight referring to the thickness of the paper backing. At 120 or more coarse, the abrasive layer is so thick the paper will have very little give. At 320 grit from most manufacturers the weight switches to 'A', a thinner paper.
Inherent rigidity will hold OK from 320 to about 800, maybe 1000 grit. After that the abrasive layer relative to the paper will begin to decrease and inherent give will increase somewhat.
I highly recommend switching to a hard strop at 800-1000 grit or at least be very mindful of pressure when going to a finer grit, especially if the bevel is narrow. Wider bevel edges, Scandi, full Convex, have more surface area and so are more tolerant of this. If using on a V bevel I recommend dropping the spine a touch - you will likely lose a degree or two/side just to the paper give. This also holds true for films to a somewhat lesser extent, but the effect is still present.
When using wet/dry over 800 grit I lay a sheet of paper over the top and compress the wet dry by rubbing it down with a piece of wood or hard plastic. Over the Washboard teeth it makes a difference, over a flat surface I'm not confident you can generate enough pressure to really compress the paper formation but might be worth a try.
You can use water or mineral oil with wet/dry, but in my experience it shortens the life of the paper. It does give a bit of extra life to papers that have been used dry and are plugged to the point where an eraser can't restore them, but only for a short bit of work.
While not very scientific, here's some micrographs of edge convexing using wet/dry 600 or 800 grit (I can't recall which).
I compared it to a:
- DMT EF hone
- Razors's edge vitreous hone estimated at approx 800 grit
- wet/dry over steel plate, all at approx 4 ozs, and
- wet/dry over Washboard at 8-12 ozs - I applied more pressure to handicap the WB, test the hypothesis that the interrupted peaks of the WB causes the same "hardening" of the wet/dry as it does with regular paper. It does, WB convex is similar to vitreous stone, maybe a touch more, but far less than wet/dry over steel plate at a fraction of the applied pressure.
Test knife was hollow grind with V bevel 420 hc steel. Pics at 40x with a "contour" feature applied to highlight the shift.
DMT
Razor's Edge
Steel plate wet/dry
And Washboard
If I think of anything else I'll add it in. Bottomline, the biggest drawback is the convexing induced by paper formation under the abrasive layer - if not taken into account you can wind up making the apex more broad than you might intend.
