Over the last year or two I’ve gradually accumulated 6 of DMT’s 8″ continuous diamond sharpening stones.  I started with Coarse, Fine, and Extra Fine per Paul Seller’s recommendation with a leather strop plus green compound for a hair-popping edge.  Then curiosity compelled me to get the Extra Extra Coarse, Extra-Coarse, and Extra Extra Fine models.  I have not purchased the special Medium stone because it costs $20 more than the other models.  I’ll be using DMT’s shorthand for these throughout this post:

Extra Extra Coarse	XX
Extra Coarse	X
Coarse	C
Fine	F
Extra Fine	E
Extra Extra Fine	EE

This post is basically shitting on those last three models.  I feel that with the C, F, and E models DMT has produced some very effective sharpening plates that efficiently remove metal to the advertised mesh.

The lowest two (XX & X) do remove metal faster than C.  But not that much faster, not $50 faster.  And I honestly have not noticed much of a difference between XX and X.  XX has sort of a bumpy, gravelly feel to it not a sharp feeling.  Yesterday I was straightening out the beefy 2-3/8″ blade on my Woodriver 5-1/2 plane blade, starting with the X plate.  You know the drill, 3/4 of the bevel is done but then the remaining 1/4 has this thin triangular section that slowly wears away.  As I spent minutes upon minutes sharpening away I there wasn’t a noticeable difference in the speed at which that triangle disappeared as I switched between XX, X, and C.  No I did not time this or get very scientific but I was frustrated from a consumer perspective.

At the top end is the EE model.  Out of the box it leaves a scratch pattern much more coarse than E and apparently requires a ton of break-in time to get good.  Some folks on Bladeforums.com have had success, this fellow spent a year breaking in his plate.  Personally I’m not willing to spent that kind of time on a product.  We’re here to make things not sharpen.  Related to this, I recently picked up an 8k Kuromaku Shapton stone and got a mirror finish coming from the DMT E plate in something like 20 seconds.  Super fast and easy.

I did spend some time trying to break in my EE plate, perhaps 15-20 minutes scrubbing with a 1″ square of steel.  It still leaves a pronounced scratch pattern after all that; I’m done with it.

Concluding Remarks

Here’s my quick summary of the plates I’ve used

Extra Extra Coarse	Way too slow for something advertised as 120 mesh.
Extra Coarse	Slower that it should be, is a bit faster than Coarse.  Also useful for flattening water stones.
Coarse	Works quickly enough, leaves a healthy surface
Fine	Works great
Extra Fine	Works great, leaves a surface that reflects light but is not mirror-smooth
Extra Extra Fine	Not worth the time investment

I feel that DMT’s plates belong in the middle of your sharpening progression.  Paul Sellers does C, F, E + strop.  Rob Cosman goes from a 1k diamond plate right to a 16k ceramic stone.

Serious shape changes can be done with the X or C plates, albeit slowly.  Or you could gently perform those modifications on your bench grinder.  Or you could do them on cheap sandpaper and a flat surface.

On the fine end a strop plus honing compound will get you a very sharp edge but you truly do need to hit it for 50 strokes.  Waterstones are an option here too but introduce more cost especially with the need to flatten them.

I’m going to stick with my C, F, E + Shapton for day-to-day tasks.  I’m keeping the X for waterstone flattening.  XX and EE are heading out to eBay.