Dull/Shiny spots along edge- why am I causing this?

C

craigdt

Joined
Dec 22, 2019
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Using a TSProf sharpener, but I had this same problem when using a Lansky, so obviously I have a technique problem.

I end up with sort of alternating dull/shiny portions along the edge.

Photos here were using Shapton Glass 220, Diamond Matrix 650, Naniwa Chosera 800.
  • AUS8 Ontario Rat
  • Mainly north/south motion, then finish with more of an east/west motion
  • Light pressure
  • Not rushing things (probably spent an hour across these 3 stones on the knife in question
  • Leading and trailing strokes, just working may way up and down the edge
The top blade is a factory edge with a consistent "shine", the bottom blade is my sharpened blade with the inconsistent dull/shine edge.

Any feedback for me?

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I use Edge Pro and do not have experience with the systems you have.
From the magnified image, some scratches don't seem to reach the apex.

So it may be either not shaping the edge with the coarsest stone or failing to remove burrs with high grit stones.
The former can be avoided by raising burrs from tip to heel with #220.
You can also check if the edge is sharp after deburring with #220 as much as possible.

The latter can happen if finer stones are thinner than #220.
I use an angle cube to make sure that each stone is at the same sharpening angle.

I am also concerned that you use stones from different manufacturers, which may use very different grit rating systems.

My 2 cents.
 
miso2 said:
it may be either not shaping the edge with the coarsest stone
...can be avoided by raising burrs from tip to heel with #220.
You can also check if the edge is sharp after deburring with #220 as much as possible.
Click to expand...

I need to look into this. Not sure I follow raising the burr portion- off to do some reading.


miso2 said:
or failing to remove burrs with high grit stones.
...can happen if finer stones are thinner than #220.
I use an angle cube to make sure that each stone is at the same sharpening angle.
Click to expand...

I did use an angle cube to make sure angles were consistent at 17.5 degrees after each stone change.
Is there another potential cause of failing to remove burrs with the higher grit stones?

miso2 said:
I am also concerned that you use stones from different manufacturers, which may use very different grit rating systems.
Click to expand...
I dont think this is an issue here- this happens on the first stone, ie, I see it with just the 220 stone, before using any following stones.
Also see this when using the whole family of included TSProf stones, and my lansky set.

Thanks very much for your feedback!
 
Guessing you use a back and forth stroke going from one edge of the blade to the other? kind of sawing back and forth? If so I would guess heavier force going one way than the other. I will do that if the edge is really worn, but when I am just renewing the apex I will start on one end and draw the stone toward me as I move it toward the other end all in one movement. from heel to toe in one glide. It makes a smooth scratch pattern from end to end.
 
The raising the burr portion, I meant that if you make sure that the burr is raised for the entire edge length, then you surely grind the entire edge with the stone, i.e. no spot left untouched.
The knife should be printer paper slicing sharp, or even toilet paper slicing sharp, after #220.
You can deburr on the stone as much as possible using very very light strokes and test the cutting ability.
If the blade does not cut printer paper nicely (there might be some hung-ups, though), then you might have failed to make the apex.

Another option is to paint the edge with Sharpie and perform a couple of light strokes like sickpuppy1 described.
Check the edge with a loupe to see if there are spots without scratches reaching the apex.
But the burr method is more sensitive.

Also, check the flatness of your stones.
Some stones dish very rapidly.
If your coarse stone is dished near the center, then it might grind deeper than the rest of the stone.

Hope this helps.
 
The dull/shiny effect can often be sort of a shifting, fluid illusion, depending on how the light hits the edge (from what direction). Per HH's post above (if I'm getting what he's saying), if the grind lines on the bevels aren't uniformly all in the same orientation, reflected light coming off of them will make the finish appear dull in one spot at a given moment, then shiny at another moment, if the viewpoint is changed and seen from several different directions, relative to the light source.

Most factory edges have been applied by some powered grinding means, either from a belt or grinding wheel. With those, the grind direction is always pretty uniform and linear, essentially perpendicular to the edge. So the light reflected from such an edge will present an even finish to the eye. But with hand sharpening, most of us will alter the direction of sharpening strokes during the work, and the scratch pattern could vary (in direction) pretty widely, unless or until we make a conscious effort to clean it up evenly, as we finish. This effect can also be seen in the errant scuffs & scratches on a satin-finished blade, from use. Sometimes the scratches 'hide' from view, depending on the direction from which the light hits them, and then stand out like a sore thumb when the viewpoint angle is changed.

This effect can also happen if coarser stage grind marks aren't fully erased in subsequent finer steps, leaving a randomized & spotty variation in the depth of the grind lines.
 
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