consistent edge thickness on thin blades

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elementfe

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May 3, 2008
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As I get deeper into training young folks to finish grind cooking knives, one frustration is teaching them how to produce really consistent edge thickness.
We do all the grinding on the tool rest, with a push stick- no jigs.
Cooking knives in particular, because of their extremely thin edges, show up every tiny variation, in the form of changing edge profile- finish sharpening highlights any thin spots as straight or less curved zones, in the worst case it makes a "Stop" when the knife is rocked on a smooth surface.

Would anyone like to share quantifiable techniques that really help with consistency from heel to tip?

(I know that by far the most common answer is, "Do Better, It Comes With Practice" and while that's not wrong, it's also not helpful. I'm looking for specific techniques I can pass along to help them boost their game)
 
I’ve seen a razor maker on YouTube sharpen the knife before he completely finishes the bevels. This lets him see where he needs to remove material from the bevel. If I am between 5-10 thousandths across the bevel I consider that good.
 
I do a similar method. I grind the basic bevel and then flatten the edge. I grind it at 45° to establish a center ridge. From there I take it down to a near-zero edge, keeping the center ridge aligned as I go.

Some folks have best results doing the final shaping on stones.
 
Normally I use a carbide tipped height marking gauge on a granite surface plate to scribe two center lines where I want my primary bevel to stop. I'll 45 the corners, but leave the lines so that I can grind up to them while establishing my flats.
That said, I'm intrigued by the method mentioned above about starting with a bevel and then just knocking the very edge off to the thickness you want. Gonna have to try that one.

BTW... something that helped me as much as "make more, practice more" was good lighting. If you're grinding in a poorly lit shop at a poorly lit grinder, there's no way you're going to see your scribe lines, or how even/uneven your edge will be getting.
 
I too work hard (struggle with) a consistent edge thickness. For me the turning point was trying to make a few usable knifes with an inconsistent edge. I knew it had to be consistent; I know why. But, it's the reality that helped me the most. Maybe it is useful to let a new maker go all the way to the end of the process to see and feel what it means. It's one thing to measure the inconsistency, it's another to see the damage.

I like the presharpening idea, D Dominick Maone mentioned. Why? Because with the thin edge, by the time you get a good burr on the thicker spots, the thin areas are simply gone leaving dips that make a kitchen knife useless. However, you are still at a point you can repair it.

So you can explain the effects of a mistake, but there's nothing like seeing that thin metal waste away on the whetstone.

(I know that doesn't show how to get it, but it sure helps with the motivation.)
 
Thank you, Stacy and Dominick!
I mark the blades with a height guage for pre-HT bevel grinding, of course, but can really see the value in reestablishing that center line for the last part of the grinding!
I'm also experimenting with going to a disk grinder at some point, since a lot of the issue I'm describing comes from only having a 2" flat (across the grinding belt) to work with- it all but
guarantees irregularities. A large stone wheel as is used in factories and Japanese shops would be a step as well, a 4" wide grinding surface would be twice as good as a 2" belt.
Only thing is that the disk grinder eats sandpaper at an incredible rate, I'd be using min. 2 sheets per blade- not an issue on a lot of blades but really adds up if you're making a mass of
smaller blades (petty, paring knives, etc). Then again, these aren't where the problem crops up, as much.

Grinding across a 2" belt is a really efficient way to make stock removal knives, but has its drawbacks.
 
elementfe said:
Thank you, Stacy and Dominick!
I mark the blades with a height guage for pre-HT bevel grinding, of course, but can really see the value in reestablishing that center line for the last part of the grinding!
I'm also experimenting with going to a disk grinder at some point, since a lot of the issue I'm describing comes from only having a 2" flat (across the grinding belt) to work with- it all but
guarantees irregularities. A large stone wheel as is used in factories and Japanese shops would be a step as well, a 4" wide grinding surface would be twice as good as a 2" belt.
Only thing is that the disk grinder eats sandpaper at an incredible rate, I'd be using min. 2 sheets per blade- not an issue on a lot of blades but really adds up if you're making a mass of
smaller blades (petty, paring knives, etc). Then again, these aren't where the problem crops up, as much.

Grinding across a 2" belt is a really efficient way to make stock removal knives, but has its drawbacks.
Click to expand...
Along the same lines as using a disc grinder, you can try grinding along the blade diagonally as you get closer to final dimensions. I find it really helps flatten out the grind before I move on to finishing grits like normal, because it increases the surface area you're grinding on. Also, the changed grinding angle really highlights the scratch patterns in any low spots.
 
Sandpaper is your friend. And a block.
Some of it IS "just practice" until your eyes see better and your hands do better.
But also, I can't get a perfectly flat surface off the platen. Sandpaper and sanding block *before* hardening takes out the machine whoopies. Then sharpen by hand, usually.
 
A little extra thicknesses at the tip and heel can be a good thing. I let mine get up to .004"-.005". I just do simple belt finishes and work the blade lengthwise on the platten. It wants to get thicker with less pressure. So long as you know why and add extra pressure when needed its ok. Getting that feel for when the belt is cutting is a big part of the process. Stock removal tends to be far more a function of pressure than time. It wouldn't surprise me if they spend an even amount of time but have different leverage and don't get consistent stock removal.
 
Michael Black said:
Along the same lines as using a disc grinder, you can try grinding along the blade diagonally as you get closer to final dimensions. I find it really helps flatten out the grind before I move on to finishing grits like normal, because it increases the surface area you're grinding on. Also, the changed grinding angle really highlights the scratch patterns in any low spots.
Click to expand...
This is how I'm doing my FFG kitchen knives, really makes a difference getting them flat and you can apply pressure to the edge side to thin it out.
 
daizee said:
Sandpaper is your friend. And a block.
Some of it IS "just practice" until your eyes see better and your hands do better.
But also, I can't get a perfectly flat surface off the platen. Sandpaper and sanding block *before* hardening takes out the machine whoopies. Then sharpen by hand, usually.
Click to expand...
Would you be willing to describe your technique?
 
DevinT said:
I keep a diamond hone next to my grinder and polish the edge a little, I find it easier to see when the light reflects off of the edge. I grind to <.002 thickness.

I also only scribe one center line instead of two parallel lines and grind until it fuzzies up the line.

Hoss
Click to expand...
Thanks, Devin
What part of this is before/after HT?
 
Storm W said:
A little extra thicknesses at the tip and heel can be a good thing. I let mine get up to .004"-.005". I just do simple belt finishes and work the blade lengthwise on the platten. It wants to get thicker with less pressure. So long as you know why and add extra pressure when needed its ok. Getting that feel for when the belt is cutting is a big part of the process. Stock removal tends to be far more a function of pressure than time. It wouldn't surprise me if they spend an even amount of time but have different leverage and don't get consistent stock removal.
Click to expand...
Thanks- when you sharpen, do you find yourself compensating for the varying thickness, or have you worked out a technique that makes it not matter?
 
Don Nguyen demonstrates on You Tube doing the 45s on the disk grinder in horizontal position until the knife is basically sharp and then grinding the bevels until the secondary bevel disappears.

You could have your students measure the edge with a thickness gauge and/or keep a large diamond stone near the grinder. Hit the stone diagonally and/or vertically and the scratches will show where the material needs removing.
 
elementfe said:
Thanks- when you sharpen, do you find yourself compensating for the varying thickness, or have you worked out a technique that makes it not matter?
Click to expand...
Your blade thicknesses won't change how you sharpen. You just stick with the bevel angle. I freehand followed by a wood strop and paper check to make sure that there aren't any dead spots. Most of the time there will be more wear in a portion of the blade. My blades are pretty thin out at the edge and only very a couple of thousandths but it gives a bit more support for the tip if it's dropped or fir heavier cuts at the heel. For kitchen knives the secondary bevel is very small because of the thin edge and the change in thickness doesn't really show much.

Depending on what steel you are using you should be able to hand sand your final edges if you are struggling on the grinder. How bad is the problem and what sort of blades are you making?
 
Take it down to 10 - 15 thou. Sharpen on a known flat surface (I use my disc grinder followed by a 400 atoma) I use the atoma to tweak and make sure my edge is centered and straight. With this straight you get an easy visual indicator (the edge bevel) to show the thicker and thinner parts. Best way I've found, still requires time and practice to get right though
 
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