Sharpening question,

[Zach Dillinger]

I like that. I fear many are paralyzed by a standard that may be considerably higher than necessity merits.
Not every planing or chisel task requires the finest finish.

My sharpening approach is "Get on with it."

+1 to this.

[Hilton Ralphs]

In my earlier days, I've used 3 DMT Dia-Sharp plates <snip> And after having 3 DMT Dia-Sharp plates that are not flat, far from "precision flatness" that you can feel the blade riding over valleys and uneven surface

David Barnett was referring to Duo-Sharp stones, not the plates you have. Different animal altogether.

[Sam Takeuchi]

I know Duo-Sharp and Dia-Sharp are different things, but if you read throughout the thread, nothing was said about Duo Sharp, until D. Burnet posted

"Sam, as a friend used to admonish his errant charges on grand rounds, "I cannot appreciate that diagnosis."

My experience contradicts your conclusions...

What I understood was that he posted that quote as an example of the characteristics of diamond stone. Was I supposed to assume that's what he was going to post that when I wrote "diamond stones don't last forever and can be work in a couple of years depending on use" before his post? In the same manner, I can say I was talking about Dia-Sharp and thus characteristics of Duo-Sharp has no relevance in this discussion? The discussion was about diamond plate, without being product specific. Because he cited someone's observation about Duo-Sharp, does that encapsulate qualities of diamond stone across the board? No, it doesn't. So I don't see why it is relevant that the quote cited mentions Duo-Sharp.

[David Barnett]

In my earlier days, I've used 3 DMT Dia-Sharp plates (only for sharpening, not for lapping stones), and they've come to be very frustratingly slow to cut and for all practical purposes, they were not at all good performers in about 2 years.

Quite frankly, most every disappointment I've heard about or personally experienced with diamond plated sharpening stones concerned DMT so I thoroughly understand what you're saying. I have one each red, blue and green disappointments to remind me of just how far an otherwise viable and worthwhile technology can stray from adequacy in flatness, quality of cut and longevity. Put simply, I hereafter eschewed all DMT products.

For sharpening woodworking tools, monocrystalline diamond plates have rarely failed to disappoint as to longevity and quality of cut, whereas polycrystalline diamond has rarely failed to please—one reason why I've long favored Eze-Lap which still is made with polycrystalline diamond, although monocrystalline has been added to the mix. Rather than monocrystalline's rapid deterioration of desired cutting characteristics, polycrystalline stones actually improve with use until finally settling into reasonably fast-cutting hones with wonderfully smooth, consistent scratch patterns.

Monocrystalline diamond is wholly appropriate for certain uses, of course, and can rapidly produce highly uniform surfaces in very hard materials, especially when aligned and distributed as found in the excellent 3M films. I use mostly monocrystalline diamond for all gem faceting and polishing on rotary laps but still prefer polycrystalline for some gems and nearly all work on metals, whether sharpening or polishing.*

An interesting comparison is explained in product literature from Pace Technologies, which I linked to in my earlier reply to Jim Matthews.

Flatness, however, is a manufacturing issue and I'm very particular in this regard. DMT does not satisfy my needs in this respect.

Also another diamond plate I've used for waterstone lapping, that a cheap, but extremely flat one was worn out in about 2.5 years of regular use, but for the price and its flatness, I think it was a good buy.

Having only briefly used diamond plates for flattening water stones, I've not experienced that degree of attrition. It didn't take so terribly long, though, to puzzle why I was still using waterstones when the diamond stones used to flatten them better met my needs—headslap!

And after having 3 DMT Dia-Sharp plates that are not flat, far from "precision flatness" ... I'm not saying they are lying or casting suspicion on their claims, but their experiences don't match mine.

Nor mine. Here again, regarding DMT, we are in total agreement.

I didn't say anything about initial aggressiveness. In fact, I wouldn't count initial aggressiveness as indicative of diamond stone's cutting performance overall either. It scratches too deeply.

While this speaks in part to the initial cutting characteristics of both crystal habits, the sharper, deeper, angular troughs left by monocrystalline stones take more work at finer grits to mitigate, whereas polycrystalline diamond, due to its initial shape and varied presentation angles, actually gets you closer to the next stone and final polishing more quickly and with less metal to remove at each step.

I know that the longevity of using diamond stone is not to put so much pressure and also spread wear (like any other stones really) ... Anyone who has had experiences with diamond stone probably know its initial cutting performance only last for a short time, so I don't know why you thought I was talking about its initial aggressiveness.

I think that last sentence could largely be attributed to having first experienced a DMT or other monocrystalline diamond hone without the opportunity to compare it to polycrystalline.

Initial cutting is linked to loss of cutting efficacy and this bears on the distinction of monocrystalline versus polycrystalline sharpening and product evaluation. The initial cut on a polycrystalline hone is initially less aggressive than most monocrystallines, and that initial aggressivenes prevails throughout a much longer break-in curve than monocrystalline stones, so would disabuse you of the notion that your experiences are unvarying or should be regarded as rule-of-thumb for all diamond stones.

It would almost appear that we're discussing two entirely different sharpening technologies, much as the two blind men drawing conclusions about how an elephant looks from examining wholly different parts.

In my opinion, it really is as simple as the difference between mono and polycrystalline diamond. Yes, there are other issues—bonding, substrates, flatness and so on—but the two different diamond crystal habits and products do manifest their differences in two polar sharpening experiences.

To be fair, I can see diamond stones lasting for a long time when combined with grinder or otherwise powered method of establishing bevel and/or doing major work and in that case, plates not being flat doesn't affect as much if the plates don't touch the full bevel.

Yes, I should clarify that I do not use diamond electrobond plates for establishing bevels and do not recommend them for that. Whether for flat, hollow or occasionally convex bevels I use powered bench and belt grinders or rotary laps for all but my narrowest chisels and certain carving tools. Also, given the speed at which I perform the hand honing parts of my regimen, diamond stones are only used for a very few strokes before proceeding to the polishing lap, so yes, this amortizes stone wear differently than one who establishes bevels and flattens tool backs.

*An interesting wrinkle that addresses some advantages once offered only by polycrystalline diamond, is the newer friable monocrystalline diamond which gives a fast and aggressive but uniform cut, breaking down evenly to a finer cut during use.

I, however, still prefer the rounder troughs left by well broken-in polycrystalline diamond for electrobond diamond honing laps.