Diagnose a profiling issue

[maximus83]

Having a challenge when profiling some blades, like this old Benchmade, where as you can see the edge bevel back near the heel is not a consistent width as the rest of the edge. Not super concerned about cosmetics and these blades are sharp, they are popping hair and doing smooth push cuts from tip to heel, but it seems like I should be able to do a little better for bevel consistency.

With some of my cheap practice blades, I keep experimenting on my coarse stones modifying pressure, etc, and I cannot figure out exactly what I'm doing wrong that makes this keep happening. Suggestions on what I need to try different?

 

[FortyTwoBlades]

In the photo the heel and tip look about the same--you just have a width increase at the belly, probably from lowering your angle as you sharpen around the curve.

 

[adamlau]

You answered your own question: Modulate pressure and angle to achieve the consistency you desire.

 

[maximus83]

I don't know if this is a fairly common issue, but I was just looking at a ZT 0561 that was professionally sharpened a while back, beautiful edge and consistent bevel throughout. Except back near the heel, where like mine, the width of the bevel thins down.

I am certain that you are both right, I am either not holding a consistent angle, or pressure, or both. But...that is unlikely the case with a belt grinder system as was used by a pro sharpener, which shows this similar thinning near the heel. Any ideas what could account for that?

 

[115Italian]

I think it has to do more with blade thickness. At the heel is where there is so much material and then back at the tip again it thickens. Lower you angle at heel. Start at the heel and slice through the stone. Start lifting when you get to the belly. If they’re coming out sharp, looks shouldn’t be a concern.

 

[maximus83]

That makes sense. Another variable is apparently the stones used. Here's another photo of the same blade, cleaned up and reprofiled on a different coarse stone. Much much cleaner consistent bevel, still a slight bit of thinning at the heel but much better bevel throughout. And still, excellent sharpness.

 

[FortyTwoBlades]

Definitely, if the grinding at the factory didn't follow the cutting line of the blade then you'll have the base of the blade the thinnest and the closer to the tip, the thicker it will be. If anything I tend to be more prone to experiencing the opposite problem when using extra coarse stones because I'll often bear down more on the heel of the blade. Is it possible that you were doing the opposite and--using a two-handed hold--were applying most of the pressure with your off hand to the spine of the knife? That would result in higher pressure towards the belly and tip, and less at the heel.

 

[maximus83]

Benjamin, anything is possible, and usually when things go awry I assume it's me doing something wrong, somewhere. I'm certain that's a factor here too. That said, it does seem like there are some variables in addition to my technique. For one thing, I can definitely tell a huge difference in this issue based on which stones I'm using. Also, there does seem to be something to the idea that the blade's primary grind may play a role.

Look at this ZT 0561, which was professionally sharpened a while back by a guy who uses a belt system. The bevel on the OTHER side of this blade is not only beautiful as here, but perfectly consistent and symmetrical. Here though, look at how it thins out down by the heel. I seriously doubt this one is due to the guy's technique, he designs knives and has sharpened stuff for 40 years, and for me for the last 7 years, and he doesn't make mistakes.

 

[Lapedog]

Having a challenge when profiling some blades, like this old Benchmade, where as you can see the edge bevel back near the heel is not a consistent width as the rest of the edge. Not super concerned about cosmetics and these blades are sharp, they are popping hair and doing smooth push cuts from tip to heel, but it seems like I should be able to do a little better for bevel consistency.

With some of my cheap practice blades, I keep experimenting on my coarse stones modifying pressure, etc, and I cannot figure out exactly what I'm doing wrong that makes this keep happening. Suggestions on what I need to try different?

The unevenness in the width of the bevel is not harmful at all. The only uneveness you should worry about is if the edge angle is uneven between the heel and tip of the blade.

I believe that along with the natural curve of the blade the semicircular motion used by many when sharpening also has a tendency to create that effect.

 

[FortyTwoBlades]

Benjamin, anything is possible, and usually when things go awry I assume it's me doing something wrong, somewhere. I'm certain that's a factor here too. That said, it does seem like there are some variables in addition to my technique. For one thing, I can definitely tell a huge difference in this issue based on which stones I'm using. Also, there does seem to be something to the idea that the blade's primary grind may play a role.

Look at this ZT 0561, which was professionally sharpened a while back by a guy who uses a belt system. The bevel on the OTHER side of this blade is not only beautiful as here, but perfectly consistent and symmetrical. Here though, look at how it thins out down by the heel. I seriously doubt this one is due to the guy's technique, he designs knives and has sharpened stuff for 40 years, and for me for the last 7 years, and he doesn't make mistakes.

Right. Hence why I said that the grind of the knife can be a contributing factor. If the way the factory ground in the primary doesn't track truly parallel with the edge you can end up with that kind of visual irregularity. I'm just throwing out various possibilities so that they can be taken into account when troubleshooting.

 

[maximus83]

^Yep. If I were to guess based on the responses and looking at a few of my other blades that I have sharpened, or that others sharpened, I think it's likely a combination of inconsistency of pressure (my bad), which gets magnified or made even worse when using an ultra coarse stone to profile, AND there can be issues in the blade grind that complicate matters. The takeaways are that a little thinning by the heel doesn't NECESSARILY mean that the person doing the sharpening fouled up. Also I think for ordinary profiling work, I could use a less coarse stone to start (something in the 200's) that doesn't take so much metal and is a bit more forgiving when profiling really hard steels. I've found that certain types of softer steels, like simple carbon steel and some Chinese or traditional stainless steels, I can profile on ANY coarse stone almost regardless of how coarse. But some steels, esp really hard ones like Elmax, S30, M390, etc, make it much harder for me to get an even consistent bevel when profiling on a super coarse non-diamond stone.

Thanks all for the insightful comments.