Diamonds and Rust

There is a long series of posts over on Wood Central about sharpening with cheap diamond paste. Most excellent. You can add diamond paste to your oil stones for that extra “edge” or put the paste on a suitable substrate, cast iron being the preferred substrate as the diamonds can partially embed themselves in it, stay put and abrade steel sliding above. I’ve been wanting to try this for a while and this pushed me over the edge (that word again, sorry).

First step, get some diamonds. You can get them direct from China via ebay, I got them from http://www.lopacki.com/ for about the same price (they appear to be the same products) at $6 per tube. I got mesh 1,200, 3,000, 14,000 & 50,000 for under $30, should have gotten 360, 600, 1,200 & 14,000 (and maybe 3000) as I’ve only used 1200 & 14,000 (there doesn’t seem to be any consistent relationship to grit, in Norton speak these would be Extra Fine and Super Extra Extra Fine. Nice chart here) and would like something coarser for initial flattening.

I was going to use the paste with my oil stones but went to the salvage yard to see if I could find some cast iron. They had a nice big surface plate but even if I could move it, I wasn’t going to spend upwards of $1k on it. After some poking around, I found a bunch of these, which are apparently used in local granaries: 25″ diameter, almost ½” thick, 36# and $0.40/pound ($14.4, same price as steel + about $1000 of my labor for maching). After machining (skim one side, hog off the divots on the other) and lapping, I have a 3/8″ (or 1/4″ if I make a big screw up) plate. One plate is 10½” long and the other is 12″, both are 5″ wide. They actually seem too big (when have you ever had a stone that is too big?!?) but that is pretty nice for “skate” sharpening.

I thinned the paste with a drop or two of mineral spirits, otherwise it was too sticky. The really strange thing is I would swear nothing was happening, it felt like honing on a block of ice but a O-1 hollow grind would just kind of vaporize. And wire edges didn’t seem to form. They were definitely there but I couldn’t feel them (I could tell by doing test cuts: hone the bevel, didn’t cut super, hone the back (remove wire edge), screaming sharp). I didn’t feel the need to strop or use a micro bevel. Very nice.

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