OldTools Archive

Recent Bios FAQ

234564 Brent Beach <brent.beach@g...> 2012‑11‑21 Re: Flattening Benchstones
On diamond stones to flatten other abrasive stones

On 2012-11-20 20:21, Joshua Clark wrote:
> I keep my waterstones flat with a 220 grit DMT stone, a good
> multi-takser that I also use for the first stages of  sharpening and
> lapping. It only takes a few swipes each time I use my stones- maybe
> 10 seconds at most.

Diamonds actually shatter the particles of the other abrasive. While 
this process may dislodge some particles, those it does not dislodge it 
shatters. Breaking off the tips.

This has an interesting result. When you break off the tip of an 
abrasive particle, almost all the time the resulting particle is duller. 
The upward facing point has a larger included angle.

   http://www3.telus.net/BrentBeach/Sharpen/Fig%2003.18.jpg

 From Samuels, showing how abrasive grit fractures. In all three cases 
the new tip is blunter than the old tip.

The larger the included angle the greater the stress (force) when the 
grit particle abrades the metal surface. The greater the stress the 
greater the resulting dislocation of the crystal matrix. The weaker the 
metal. The faster your tool will dull.

Diamond is unusual in this regard. Most other ways of flattening will 
dislodge grits, not fracture them, because the second surface is not so 
much harder than the stone you are flattening. In the case of flattening 
on cement, the second surface is softer and will almost always dislodge 
grits rather than fracture them.

Waterstones have a soft binder - grits are more likely to dislodge 
rather than fracture. The harder the binder the more likely you are to 
get fracturing.

The tips also fracture during use of course, so there is some dulling of 
the abrasive. With sheet abrasives, there may only be one layer of grit 
particles. Once they get dull, time for a new sheet. With stones, 
getting one with a good balance between binder hardness which allows 
duller grits (which because they exert more pressure are more likely to 
pop out) to pop out refreshing the surface, is the key. Too soft, even 
sharp grits pop out. Too hard, too many dull grits.

Brent
-- 
Victoria, B.C., Canada
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Recent Bios FAQ