Chinese cleaver edge not straight. Help?

[Loren Jones]

Hi,

My first knife making attempt is a chinese vegetable knife/cleaver in CPM M4. It is a thin knife about .060 at spine and .010 behind the edge. The edge profile is nearly straight with very little belly. Unfortunately I have several spots where the edge has some low spots and some high spots that prevent it from contacting the cutting surface smoothly along the length of the blade when I cut. It leaves a bit of uncut food unless I do a push or draw slicing cut.

I think this is because I didn't have the behind the edge thickness the same along the length of the blade. My theory is that I had some spots that got thinner behind the edge and when I put the edge bevel on and sharpened it the thin spots ground out to an apex sooner and then turned into little hollows. Does this seem right?

How should I fix it. I'm not skilled, this is the first knife I've attempted. I have a 2x42 grinder. I did the edge bevel and sharpening with a Hapstone guided system holding 3" x 8" atoma plate. After discovering the problem I went back to the hapstone with the atoma 140 and attempted to use it to grind everything straight and it keeps creating these hollows that don't contact the cutting surface.

Here is a pic of it against a flat cutting board. Notice the wavy edge and alternating hollow spots and points of contact.

IMG_0898 by Loren Jones, on Flickr

Here are some other pics of the knife and of the little wharncliffe I made from the handle cutout that I use as a package and letter opener.

IMG_0884 by Loren Jones, on Flickr

IMG_0883 by Loren Jones, on Flickr

IMG_0886 by Loren Jones, on Flickr

IMG_0904 by Loren Jones, on Flickr

 

[HSC ///]

Yes your analysis is correct. You have overgrinds and low spots.

You could hand sand finish it on top of a flat block, blade clamped down. Use a rigid hard back flat piece for the sandpaper.

you could also get a 220 stone and hand polish it to take the high spots down

if you can’t regrind it even, then there’s no substitute for sanding with elbow grease

 

[Loren Jones]

Thanks HSC. I will attack it that way.

 

[Scaniaman]

When that happened to me, I had done all the grinding vertically. Grinding things at 45 degrees or so on the platen helps to keep things straight and even. It gives a greater area of contact between the platen and edge to be.

 

[FredyCro]

You didn't mention it, but what kind of platen does your grinder have? My smaller grinder improved significantly when I added a hardened platen. You could have an appropriate sized piece of A2 or D2 hardened and epoxy it to the grinder, pyroglass or a piece of ceramic tile are also a possibility.

 

[Stacy E. Apelt - Bladesmith]

When I need an absolutely straight edge, I grind the blade to a zero edge ( no secondary) and after finish sanding I set the edge on a diamond plate and give it a couple strokes until it is dead flat. Then I do the secondary bevel.

 

[scott kozub]

Long flat spots are very difficult because they show every little imperfection. Stacey's advice is great. Also make sure that when you are sharpening you keep checking for burrs. Once a burr gas been raised move to a new spot or youll sharpen in a hollow.

 

[butcher_block]

i think you ll have that fixed up fairly easy using the above posted fixes. for the grinder used thats not bad. i like to change up the grinding direction for 2 main reasons it helps cut down on "holes" in the edge like you have and shows last belt grit scratches. when i say grinding direction im talking edge perpendicular then tip up and then tip down at say 45 degrees ISH. kitchen knives really are good at showing any and every issue that might have been ok on other knives or at least not as big a deal over all

 

[Cushing H.]

Taking a slightly different approach - is there a compelling reason you wanted the edge flat? As scott said, they show every little imperfection ... also, they just do not work well to cut food (dynamics wise). I have, what ... four cleavers ( I’m loosely lumping one nakiri into the category), and they *all* have some belly to the edge...

 

[Loren Jones]

When that happened to me, I had done all the grinding vertically. Grinding things at 45 degrees or so on the platen helps to keep things straight and even. It gives a greater area of contact between the platen and edge to be.

Yes. I definitely did all the grinding vertically and I’m sure that’s how it happened. The 45 idea sounds helpful

 

[Loren Jones]

You didn't mention it, but what kind of platen does your grinder have? My smaller grinder improved significantly when I added a hardened platen. You could have an appropriate sized piece of A2 or D2 hardened and epoxy it to the grinder, pyroglass or a piece of ceramic tile are also a possibility.

The platen is a piece of 1/4” mild steel that I ground flat on a disc sander and glued and bolted to the platen.

 

[Justin W]

I do a few things in my process to help keep a consistent bevel.
1. I start with the 45° edge to mark the centerline and make it as consistent as possible.
2. I grind with a jig at 90 degrees (blade horizontal, belt vertical). But after I get close, I do a freehand grind with the blade at 45° tip down, edge up. This changes the scratch pattern and will show you places where the grind isn't even.
3. When I start to hand sand, I start with my coarse paper on my flat reference surface (scrap countertop piece). Lay the blade flat and sand it 90° again. Since you have 45° lines from step 2, this will show how flat everything is. Bonus, it also fixes imperfections gradually.
4. Once you get down to 0 TBE draw the edge in a slicing motion on your paper on the flat surface. Just a couple passes. Then feel the edge by rocking it on the flat surface to feel for bumbs in the profile.

 

[Loren Jones]

When I need an absolutely straight edge, I grind the blade to a zero edge ( no secondary) and after finish sanding I set the edge on a diamond plate and give it a couple strokes until it is dead flat. Then I do the secondary bevel.

That’s a good idea. After playing with this profile a little I am realizing that I don’t want a large flat spot to the profile, just something with very minimal belly.

But I do love wharncliffe for edc blades and your technique should come in handy there.

 

[Loren Jones]

Taking a slightly different approach - is there a compelling reason you wanted the edge flat? As scott said, they show every little imperfection ... also, they just do not work well to cut food (dynamics wise). I have, what ... four cleavers ( I’m loosely lumping one nakiri into the category), and they *all* have some belly to the edge...

I thought I wanted a really long flat spot at the back 1/2 of this cleaver with a small belly at the front. But after trying this one out a little I realize that a little bit of belly is needed. If there is no belly and you don’t bring the flat down completely parallel then it feels awkward.

I’m going to change the profile to be a slightly understated version of what is on a Nakiri I have and then I will get the thickness behind the edge consistent with some of the methods mentioned above and hopefully I’ll be in business.