Annoying two-inch bump screwing up my edge profile after sharpening - how to fix?

[Goot]

I have a recurring problem with the edge of my chef knives after I begin sharpening a finished knife. The bevels are ground, everything else is done, and the edge profile is good and flat near the heel. However, when I finish sharpening and check the edge against my granite slab, I notice that there's a small divot in the edge about two inches from the heel that lifts away causing light to shine through. It's not super apparent, but it's enough to be a problem. It's a pain in the neck to fix especially when the rest of the blade is sharp. See the picture above with the red divot.

I figured that this was occurring due to an uneven bevel grind -- the "two inch divot" referenced by Walter Sorrells in his youtube video. I made a new knife making sure I was being careful with my body positioning and angles on the platen, but it happened again! I'm getting to the point where I want to make the belly larger near the heel in my initial profile to mitigate this, but that's not solving the problem. It only starts showing as I'm sharpening.

Am I on the right track with the cause of this? Do I just need more practice grinding bevels?

 

[Alden Cole]

How are you sharpening? I'm thinking you may be putting more pressure or time on that one area than the rest of the edge while sharpening. I think I used to get that "recurve" unintentionally when sharpening with the 1x30.

 

[John Wilson]

If you are sharpening on a belt, my guess is that you are starting each pass at the same point (the heel). The belt always has a bow in it, and if you are setting the knife down and making the belt go flat that spot is going to get sharpened away as it makes first contact.

This is a problem with all belt sharpening. On a 2x72 it’s often very helpful to do your sharpening with the big contact wheel in place. You can still use the slack belt but that wide wheel keeps the belt flatter than the narrower wheels on the platen (at least on my machine). The Wheel is also handy for straightening out this divot. When I have an edge that is too thick, sharpening directly on the contact wheel is the way to go because you’ll eat an edge trying to remove thickness on a slack belt. You can also do all of this on the platen but the frame is always in the way on the left side when you want to use that stiff gap between the top wheel and the platen. And sharpening on the platen itself seems to magnify the splice more than the rubber contact wheel does.

 

[vlegski]

What John said. Plus it applies to any mechanical sharpening system. Its a natural tendency to hesitate a split second as we set the blade into sharpening system. That hesitation means that area of the blade gets a fraction of a second longer contact with grinding medium. Hence that slight divit

 

[Edwardshandmadeknives]

Could be sharpening like John said. If you have a disc grinder, try using that for sharpening.

 

[Andre Grobler]

Lead with the heal in the initial bevel grinding, and go easier with it, as you go

 

[Goot]

Yeah, I'm using the sharpening system from HouseWork - same method in this video. I might try what John said, and use the big contact wheel and see how that goes. Thanks for your feedback!

 

[John Wilson]

That’s a good video. Hadn’t seen that one before. I notice that he’s running the belt super slow and using a lot of dwell time as he makes his pass. The main thing that I see is that he’s very very consistent with his passes and isn’t spending any extra time on any given spot. His slow passes appear to help blend any dwell related issues he might otherwise have.

I run my belt at about 50% and make my passes faster. I also don’t run in reverse. Horses for courses, and all that. Like he said, it’s very much a feel thing where the object is consistency.

 

[Taz575]

I had this a lot on kitchen knives. I really had to focus on where my grind started and keep the thickness at the edge even, especially if I don't have a clear plunge cut in the blade. Get the blade with no divot, but that area would often be thinner than other areas behind the edge and when sharpening, the divot would come back. I started paying more attention to the edge width on the blade and making sure I didn't get it too thin, especially when convex grinding on a felt or rotary platen. It can happen up at the tip too. If I belt sharpen, I do it on a slack portion of the belt just past a wheel where there is still a lot of tension on the belt since the belt itself can cup a bit. I rough the edge bevel on the belt sander and then switch over to waterstones by hand after the intial bevel is cut by the belt at 120.