Jason B.
Knifemaker / Craftsman / Service Provider
- Joined
- Jun 13, 2007
- Messages
- 11,184
Am no expert and the following is mostly speculation, but a lot of what determines this comes down to the condition of the abrasive surface itself.
An AlOx stone in good condition will make a nicer rough edge than a loaded SiC stone. SiC has the advantage of, while being hard, it is also not durable. Under good conditions as it breaks down it is always presenting a sharp surface, and it breaks down with less pressure than most forms of AlOx. Of Diamond, SiC, or AlOX, AlOx is most likely to glaze somewhat, being more durable but not as hard - so while still tearing out metal it isn't doing so with the sharpest of tips. Diamond also does a good job but over time it too will 'glaze' and the tips won't be as sharp. If you let your SiC stone load or glaze it will underperform. Keep up on it and it will maintain the sharpest contact points.
Keeping in mind the individual abrasives depending on how they are arranged will either:
- cut with sharp projections - clean stock removal - low burr formation per unit
- plow with a projection that isn't sharp - stock dislocation, lower removal rate - higher burr formation per unit
- rub with a relatively smooth stretch of surface - stock dislocation, no removal - plastic deformation
You can only manage so much of this, there is always going to be a variety of each in a given surface, and the rake angle of any given mechanism is going to change as well. As the minerals glaze (dull), the surface area increases - unit pressure goes down, depth of cut decreases, condition of the steel at the apex is more prone to drawing out/burr/wire edge. With a finer abrasive, this effect isn't as pronounced or might even be desirable (combined burnishing and abrading action of fine ceramic surfaces). At low grit levels this can leave you with a drawn out edge, low stock removal rate.
Combine that with the low abrasive density/ high unit pressure and many of the abrasive tracks will finish with a single pass trough being cut - there is no easy way to cleanly remove a burr from the opposite side esp if it is lower than the surrounding area - the quality of the abrasive cut on every pass becomes very important.
Also keeping in mind the main difference between a coarse abrasive field and a fine one is mostly the inherent spacing of the abrasives themselves and the effect this has on footprint (unit pressure) and relief areas for the removed stock to go. If you took 5 micron abrasives and mounted them to a 'bed of nails' in a 120 grit open pattern, it would cut far more like a 120 grit stone than a 1200 grit stone.
The rough abrasives will leave the edge irregularly cut both along the edge and across. Generally, a leading pass into the edge will tend to make more variation across the edge compared to a trailing pass. A trailing pass will tend to make more variation along the edge. On the down side it is very tough to manage burr formation on a trailing pass - the mineral has to have some mobility so when it bites it doesn't lodge into the steel and draw it out as it grinds - it will shift itself free if the resistance gets too high.
And then in some cases depending on HT and alloy content, a given steel may or may not take and/or hold a rough edge well, no matter how its created.
If the steel is soft enough, a file probably makes the best toothy edge, followed by SiC.
Very nice Martin, I really like the illustration.
Now that I have all the waterstones I could ever need I might just start up an oil stone collection
Picked up a little Ace hardware stone today, knife went dull at the job site so I needed something, so far so good. It's harder than my Norton and is a little easier to get rid of the burr. My fine Norton SiC stone is as muddy as a King stone and always seems to wash out the apex.
