Hand Tools

Subject:
Re: Diamond scratch depth
Response To:
Diamond scratch depth ()

david weaver
Wiley, I think all of your comments are right (I didn't check your math, but the precise number isn't important, the sentiment about removing a depth of metal against an acute angle below is correct).

As far as toothiness, that's precisely what's going on. The diamonds create tooth - even when they're a tenth micron, they create tooth. I suspect that either this toothiness or the loss of it and the slight rounding that results creates the very transient sharpness feel that diamonds have. The transient feel is, i'm fairly sure, responsible for the errant assumption that too fine of an edge doesn't hold. of course, there is a transient feel, but the absolute (nominal if you could measure it) sharpness after it's gone is still at least as good or better than a less well finished edge. Certain things favor this edge chasing more:
* harder irons that also don't chip
* harder wood that takes better clearance to be cut properly, and also is more of a challenge to the edge
* tiny shavings that only get removed from a surface well if the edge is reasonably thin and also has excellent clearance

These little teeth also punish people when shaving, so even something like a 0.25 micron diamond is often followed with 0.5 micron chromium oxide pigment.

The real question for woodworking is when do the grooves get big enough to have a material acceleration on edge failure, and the answer, I'm sure, includes a whole list of factors:
* how thin of a shaving
* how long does sharpening take
* how often is it acceptable to redo it
* at what point do the tiny lines actually show up on the surface of something (and is it OK if they do - plane, scrap, sand routine isn't going to care about tiny little lines showing the exact path of the plane)

I think the 1 micron diamond size is a very good compromise in terms of fineness and edge life vs. speed, and I don't think any of the tiny scratches in the microscope picture are going to be showing up on a planed surface.

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