How to sharpen a chisel grind

[maximus83]

Anybody have tips on how to sharpen a chisel grind?

Did one of my wife's cheap kitchen paring knives this weekend, it was a chisel grind. First one of those I've run into.

What I did: edge reset on 300 diamond, finish on 1200 diamond.
What was weird:

• Only sharpening on one side.
• It kept getting a burr on the back non-edge side. So I had to keep flipping it over and dragging that burr with an edge-trailing stroke on the stone to cut it off. I suppose I did something terrible there , but this is like a $3 knife and I was just playing. And I couldn't think of a better way to deal with that. In the end I got it sharp.

 

[jalapeno]

An important step in sharpening an actual chisel is flattening the back. You can't reach peak sharpness by working just the bevel. (You can still get it sharp, just not as sharp as it could be if you work it from both sides).
Some people will flatten the back to mirror finish first. But you really only need to focus on the part of the back near the edge.
Since it's just a small paring knife and not a good one, you might experiment with flattening the back on a series of bench stones first. Or, buy a cheap 1-1.5" wide chisel and practice on that.

As an example, here's a chisel grind CRKT backside (painted black from the factory), flattened and polished with waterstones:

 

[FortyTwoBlades]

Edge leading strokes will cut off a burr easier.

 

[maximus83]

Cool knife! So, by "flatten the back", you mean I just need to grind the entire back surface? In my case, I don't have a large set of stones to do all that nice finishing work like in your picture. Since this is a user knife, that's ok and I would just need to polish it enough to get the deep scratches out. I think the only stones I have that could do any real polishing (versus just scratching the heck out of the back side of the blade ) would be my 2 Baryonyx AlOx bench stones. The Ptarmigan is rated at 6K JIS and cuts pretty fast on soft steels like this paring knife, so I assume it will do some polishing.

An important step in sharpening an actual chisel is flattening the back. You can't reach peak sharpness by working just the bevel. (You can still get it sharp, just not as sharp as it could be if you work it from both sides).
Some people will flatten the back to mirror finish first. But you really only need to focus on the part of the back near the tip.
Since it's just a small paring knife and not a good one, you might experiment with flattening the back on a series of bench stones first. Or, buy a cheap 1-1.5" wide chisel and practice on that.

As an example, here's a chisel grind CRKT backside (painted black from the factory), flattened and polished with waterstones:

 

[maximus83]

Edge leading strokes will cut off a burr easier.

Cool. But I assume on the back side of the chisel-ground knife, I want to avoid starting to create a bevel, correct? That was the ONLY reason I did edge-trailing, I was just guessing that it would be easier to avoid starting to create a bevel.

 

[adamlau]

Go ahead and create a small 5 and under bevel. You are not likely to notice the minor reduction in sharpness and it will track better through foods.

 

[jalapeno]

If you have a reasonably fine stone, maybe 10 seconds of work on the flat side of your paring knife will give you some idea of how flat the back is to start with. If you have low spots that are relatively far from the cutting edge, don't worry about flattening those out. If you have high spots, you'll have to abrade those out in order to judge how flat the back is (i.e. they get in the way of assessing flatness).

I suppose you could avoid flattening the back by creating a back bevel (making the back bevel the "flatness" reference for where it meets the front bevel). But once you do this, you can't really go back to an approach of flattening the backside since you'd have to remove a lot of metal to grind away the back bevel you created. I'd only consider this approach as a last resort if the back is so "unflat" that the amount of work to flatten it is not worth the time.

 

[FortyTwoBlades]

Cool. But I assume on the back side of the chisel-ground knife, I want to avoid starting to create a bevel, correct? That was the ONLY reason I did edge-trailing, I was just guessing that it would be easier to avoid starting to create a bevel.

What you do is lay the spine on the stone and then pivot on it to drop the edge to the surface. This is what's done on straight razors for similar reasons--it avoids accidentally pushing into the abrasive at a lifted angle and creating a secondary bevel.

If using sandpapers for this work then edge-trailing will certainly be less liable to cause the paper to bunch up and create a secondary, but for such work it's recommended to use something like spray adhesive and a float glass backing to make sure it doesn't lift in the slightest.

 

[Obsessed with Edges]

Anybody have tips on how to sharpen a chisel grind?

Did one of my wife's cheap kitchen paring knives this weekend, it was a chisel grind. First one of those I've run into.

What I did: edge reset on 300 diamond, finish on 1200 diamond.
What was weird:

• Only sharpening on one side.
• It kept getting a burr on the back non-edge side. So I had to keep flipping it over and dragging that burr with an edge-trailing stroke on the stone to cut it off. I suppose I did something terrible there , but this is like a $3 knife and I was just playing. And I couldn't think of a better way to deal with that. In the end I got it sharp.

Burrs on 'cheap' low-alloy stainless are most easily dealt with by stropping with some simple aluminum oxide polishing compound on a substrate like denim or linen over a hard/firm backing (wood, glass, stone, etc). White rouge (usually in stick form), Flitz or Simichrome pastes, or Mother's Mag wheel polish (also a paste) work well. Flip the burr toward the back (flat) side; then lay that flat side flush on the strop and strop it off (edge-trailing passes, obviously). Give it a few very, very light passes on the bevelled side too, if you wish. A strop of 12"-18" length works very fast, and makes for a much more intuitively comfortable stropping motion as well.

For a $3 knife, I'd not waste a lot of time or effort trying to flip the burr or grind it off. The steel is soft and ductile, and those burrs will often just flip back & forth all day if you chase 'em that long. The stropping method above EATS BURRS LIKE THESE FOR BREAKFAST. It'll polish these steels very fast as well.

Edited to add:
Since you're finishing on a 1200 diamond, any burrs showing up are likely a sign that pressure could (should) be lighter. With a diamond hone on such soft, burr-prone steels, the lightest-possible feathery touch is all that's needed in the finishing strokes, literally as if you were just brushing dust off the surface of the hone, with the blade's edge.


David

 

[chiral.grolim]

Just so it's clear, and this has been mentioned above, if you do not 'true' the flat side of a chisel-grind when sharpening, then you might as well sharpen the microbevel you've created in that side through wear alone, else you need to grind off a lot more metal to get back to the true flat.
Here is a diagram constructed by Steve Elliot from micrographs of wood planing blades wearing over time - please note that this is the apex of a chisel-ground blade, the view is simply close enough in that you cannot see the shoulder on the one side:

 

[l1ranger]

What you do is lay the spine on the stone and then pivot on it to drop the edge to the surface.

this is what how we did it with actual chisels when I was doing timberframing - then an edge leading stroke(s) on a diamond plate.
followed by flattening the opposite site with a circular motion

 

[tiguy7]

You don’t have enough suggestions. Here is 1 more. I wipe the burr back into the sharpening plane on the side of a ceramic knife blade (edge trailing). The ceramic blade is very hard and smooth. It acts like a burnishing tool. Because it is curved, a burnishing tool might roll some of the edge into the grinding plane.