Note a steep micro-bevel will turn into a flat as you increase the angle, a flat is just an apex ground at 90 dps. I have not looked into the question which may be of interest which is what is the exact apex thickness required to prevent that initial early edge loss. This isn’t because it isn’t an interesting question, in fact for many people it might be the exact question they are interested in - however it isn’t of critical importance to me due to how I use knives in general.
Personally for example I would rather sharpen a knife which can cut 1/2" hemp with 5 lbs on a draw and sharpen it after say 100 cuts so it never gets more than 10 lbs. I would not sharpen it so it starts at 10 lbs but can do 1000 cuts before hitting 20 lbs. Now I am using hemp more or less as an example here as the numbers are straightforward and everyone can cut a piece of hemp. But in general I prefer knives which are ground to cut very well and sharpened for the same.
When I sharpen garden tools for digging, depending on who I am sharpening them for, I will either run a light flat (20 microns thick) or a visible flat (50 microns thick). It mainly depends on how much force they use and the kind of ground. If I don’t know anything about them I just do the 20 micron flat first and when I sharpen them again I just look at the edge and then ask them a few questions. If they note they saw early degradation and there is visible damage I will thicken it. By they way the reason I pick 20 microns is that is how thick an apex gets when I can see it.
For sod knives and similar I do xx-coarse finishes and cut the edge bevel as low as it can get and not deform and thin out the primary the same. Again this depends on the individual but if you make an effort here you can really see large practical gains in cutting ability which will keep the blade cutting a long time. If the cutting is light and the soil is not so rocky I have gone as low as :
-0.015"/5 dps
With a 36 grit microbevel at 16 dps, this stays very aggressive for a long time and is so easy to sharpen that a lot of people will do it themselves. When I get it back normally the knives have thickened so that much of the 5 dps edge bevel has been consumed by the repeated applications of the 15 dps / 36 grit edge.
Now if the weeder is a lot more aggressive I have gone up to :
-0.025"/10 dps
and I don’t run a true micro-bevel but another bevel at 20 dps (again at 36 grit) which is big enough to see. The trick as always is just set the thickness at the point where it stops deformation. This maximizes cutting ability and maximizes the amount of wear it takes to reduce sharpness to a specific level.
[quote quote=“razoredgeknives” post=20037]
[…]
Based upon this reasoning, could we not say that, when it comes to push cutting through hard objects, a 17 dps mirror finished edge would theoretically have the same edge retention as a 15 dps coarse edge?[/quote]
If the apex isn’t deforming, then the 15 dps edge will have higher edge retention, if the apex is deforming then it will be the 17 dps edge. The reason this happens is that a lower angle will require more material to be worn away to reach a given apex thickness (which is what determines dullness).