Magic Marker

[rayback]

I need some clarification please when using a magic marker to determine if we are on the right track when sharpening.

Let's for example, use a knife with an unknown bevel angle, and mark its bevels with a marker.
We are trying to put a 15 degree angles on the bevels.
If we notice that the area near the very fine edge has been cleared, it means that our knife's bevel angle is lower than 15 degrees.
If we notice that the shoulder of the bevel has been cleared, it means that our knife's bevel angle is greater than 15 degrees.

Am I correct?

Thanks
Ray

 

[Cliff Stamp]

Yes. One thing to be aware of is that some manufacturers put a very obtuse micro-bevel on their knives that you can't see. So the main bevel can be for example at 15 degrees but there can be a small additional bevel at 20 which is only 0.1-0.2 mm wide. If you use a marker and sharpen at 15 degrees you will see it being abraded all along the edge but the edge will not get sharpened until that additional 20 degree bevel is removed. This is one of the common sources of frustration when people start sharpening because it looks like the edge should respond but nothing happens. With modern very hard to grind steels and fine stones it can easily take a 100+ passes to remove than additional and obtuse bevel.

-Cliff

 

[rayback]

Thanks for the reply Cliff.
I think I've ran into such a problem, I'm trying to sharpen a kitchen knife, it's a stainless steel, the edge is already pretty sharp, it slices very well, push cutting not perfect.
I marked the edge with a marker, then tried to pass it few times over an aluminium oxide benchstone.
It didn't hit the edge at all by the marker, or if i'm not mistaken, it hit only near the edge.
The target angle was 15 degrees.

I will be getting a new waterstone soon from Lee Valley's Tools, 1000x/4000x combination stone, I'm gonna use it and post some results here, hope to put a better edge on that knife.
How quick does a 1000x grit waterstone remove steel? Let's say reprofiling an edge from 20degrees down to 15degrees?

-Ray