sharpening grit?

Ernie1980

Ernie1980

Joined
Apr 19, 2012
Messages
8,099
Greetings BF!

I, thanks to advise here, can now sharpen a knife reasonably well. However, I have a couple of questions and have found only conflicting information.

1. Is there a benefit in terms of edge holding to take a knife to a polished edge?

2. What is the point of "diminishing returns" where you are just further refining an edge but really not getting any sharper, instead you are only wasting time and metal. Or....making the knife lose its edge holding length of time for really keen cutting for a short amount of time.

Here is the reason I am asking, with pictures to help.

Here is a knife that I sharpened to 600 grit, then stropped the burr off. Quite sharp and I really like the matte finish the edge has.
photo 1.jpg

Below is a knife that I just sharpened to about 8000 grit (3 micron). It is razor sharp but I really don't like the hazy look to the edge. (The pic does not really show well but the edge looks like a fogged mirror)
photo 2.jpg

* so here is my real question I guess: Should I leave my knives at 600 grit and burr free or go up to about 1 micron where I can get a more polished looking edge? If there is a benefit I don't have a problem buying the additional materials and going up through more grits, but I don't want to waste time, money, and metal for little benefit. If it is better to go for the polished edge, where do I stop? 1 micron, .5 micron?

any and all help/links are greatly appreciated!
 
1) Yes and no , depends on what you are cutting. "Toothy" low grit edges have large teeth , when these teeth break off the plateau where the apex used to be will be quite wide , going from sharp to dull quickly. When smaller teeth break off a much more refined edge , the plateau they leave behind will be much smaller , this feels like a sharper knife than the degraded "toothy edge" and will stay in that middle zone of acceptable sharpness for longer. But they will be less durable doing certain tasks.

But overall I feel that edge geometry and steel type play more of a role in edge retention than finish does. Heres the kicker , to touch up a more refined edge is much easier than touching up a coarser edge , and removes much less material. If my EDC has a 0.1u finish , then to touch up I typically either just use strops (0.25u , 0.125u and 0.1u) Or if I the edge is really degraded then I go up to the 30k shapton (0.5u) and correct any damage and then go back to the strops.

2) I haven't found it yet. And I play with stuff finer than 0.025 micron.. Leaving a coarse edge hogs off the life of a knife in a hurry as you touch up and do repairs overtime.

3) You can stop wherever you feel like. If you like the performance of the 1u edge more than the 600grit edge then go for it. If the edge is not holding as well as you would like tweak the geometry a little bit.

FWIW an 8k edge should start looking like a near perfect mirror , if its looking hazy or anything like that then you probably need to do more work down low before moving up.
 
Thanks for the reply! I was wondering about the touch ups also and that makes a lot of sense. I want to take off as little material as possible and get back my edge.
As for the 8k being a mirror......you are saying just spend more time at say 1k and up to remove deep scratches?
 
I would suggest getting a loop so you can see what is going on with the edge. Helps a lot when you can see what is going on at each step.

I agree, at 8k, it should be looking pretty shiny. Are you using any compound on your strop?
 
It's not been proven that a sharpened edges teeth break off. Nor, is it true that a coarsely sharpened edge goes from sharp to dull quickly. Many gents on here have proved the opposite is true within cutting tests. That coarsely sharpened edges last longer at or around 200grit. DM
 
I use DMT diamond paste on my strops. David, do you have a test I can reference about the edge retention?
 
The difference between a coarse edge and fine edge is much smaller than many people think. The steel hardness and inclusive edge angle mean so much more it almost makes steel type irrelevant.

For most of the fibrous things a pocket knife encounters a edge in the 300-1000 grit range is often more than sharp enough and gives the edge enough bite to cut smoothly. If your using diamond hones then the 600 mesh edge will be about the best to use for a EDC, its not so coarse you need to saw the cut and not so fine that is glides on what needs to be cut.

As for how a knife dulls,

The large teeth of a coarse edge do not "break off" that's just not how it works. The irregular "teeth" of a coarse edge just like any sharpened edge becomes blunted by abrasive wear which "polishes" away the sharpness. The difference is that while the polished edge and coarse edge both have the same amount of cutting potential the coarser edge maintains a higher level of control during the sharpness peak of the blade. This gives the perception that a coarser edge is lasting longer when its just offering more control.
 
I sharpen my knives with the paper wheels, in which the grit wheel is 180 grit. I then polish/strop with the slotted wheel coated with a white polishing/grinding compound. The edges left look very close to what you are showing in your 8000 grit photo. They are quite smooth and near mirror finish, with little or no toothy edge feeling. I usually drag a Q - tip over them without the least amount of hang up, showing there is a smooth, not toothy edge on the finished edge. I have no problem with the edges staying sharp, if the geometry of the edge and the steel type is of a type that will hold an edge regardless of how it is sharpened.

If I need a toothy edge (like on my kitchen knives for slicing meat etc.) then I have to run them over my DMT fine diamond stone to get that desired edge finish. So, I would say in answer to your question, that you can stop at your 600 grit stage if it produces a sharp enough blade for your uses. You need only to remove enough steel in your sharpening procedure to acquire the needed sharpness for the job your knife is to perform for you. Any more is shortening you blade's lifetime. A mirror finish is great for "bragging rights" in my opinion, but in reality not necessary to preform most knife tasks. Just my unsolicited two cents worth! :)

Blessings,

Omar
 
Ernie1980 said:
I use DMT diamond paste on my strops. David, do you have a test I can reference about the edge retention?
Click to expand...

I first posted my methods and cutting tests results in 2008 or 09 around Sept. on cutting 1/2 sisal rope using many steels. Only changing the grit at which it was sharpened. The results are certainly an eye opener. Several folks followed expressing the same results. This is talked about much here. Some here don't like these findings and the topic when brought up is 'hotly' debated. It's ok if you like to sharpen to a higher grit. DM
 
Thanks all for the responses! I read through the Ankerson test, and see where he did the test with a 6k polished edge and then a 400 grit edge. I see the categories for the first test but not number of cuts unless I somehow over looked it. Thanks for all of the help everyone!
 
knifenut1013 said:
The difference between a coarse edge and fine edge is much smaller than many people think. The steel hardness and inclusive edge angle mean so much more it almost makes steel type irrelevant.

For most of the fibrous things a pocket knife encounters a edge in the 300-1000 grit range is often more than sharp enough and gives the edge enough bite to cut smoothly. If your using diamond hones then the 600 mesh edge will be about the best to use for a EDC, its not so coarse you need to saw the cut and not so fine that is glides on what needs to be cut.

As for how a knife dulls,

The large teeth of a coarse edge do not "break off" that's just not how it works. The irregular "teeth" of a coarse edge just like any sharpened edge becomes blunted by abrasive wear which "polishes" away the sharpness. The difference is that while the polished edge and coarse edge both have the same amount of cutting potential the coarser edge maintains a higher level of control during the sharpness peak of the blade. This gives the perception that a coarser edge is lasting longer when its just offering more control.
Click to expand...


Good post ^.


As to the OP, a lot of it comes down to your maintenance and usage. There are tough jobs for which a refined edge is entirely unsuited and you'll be sharpening your edge every day. There are finer jobs for which a coarse edge simply won't perform at all. In terms of maintenance I find something in the 4k JWS works great for maintenance as it can still do some repair work, but is also plenty refined for most tasks (though I prefer an edge just a touch rougher for utility work, I find it a bit more effort to maintain quickly). Trying to maintain a finer edge - in my experience - will involve multiple steps over time and frequent returns to the stone to maintain good edge geometry at the apex - 6k-10k abrasives just cannot repair an edge with any wiggle room. On the other end of the scale, abrasives in the lower end do not work so well on a strop compared to working on a stone, and then will usually require multiple steps of touch-up/burr removal/final finish.
In the 2k-4k range (1000 - 1500 ANSI, 5 micron) you can get a good, fast touch-up with minimal burr formation and max edge repair. Abrasives in this range also work well on a hard strop or when backhoning on a waterstone. Done well, they can still be plenty "toothy" and are narrow enough across the edge to pushcut nicely.
Tough to make generalities, for tough draw -cutting work, go coarse as DM recommends. For chopping, carving, shaving, go finer. For a combination of attributes, go in between. In my experience the edge type that performs with the least amount of pressure will last longer for a given chore.
 
Here, I'll give you some numbers. On my cutting tests one end of the sisal rope was held in a vise the other in my fingers and cuts were made near my hand. The blade never touched any other thing except the rope. Using 425M steel and sharpened with a guide on Spyderco's white ceramic stone of 1800 grit, this made 400 cuts. Before it started skating. Taking the same blade and sharpening it on a X-coarse DMT stone of 220grit it made 1450 cuts before it started skating and was reluctant to bite in and cut the rope. Either edge afterward could still manage to clip hairs off my arm. I also did several other steels with the same pattern emerging. DM
 
So it comes down to usage. Camping knives courser and slipjoints and finer work more polished edge. If I am bored enough during my upcoming days off maybe I can run my own mini test!
 
David Martin said:
Here, I'll give you some numbers. On my cutting tests one end of the sisal rope was held in a vise the other in my fingers and cuts were made near my hand. The blade never touched any other thing except the rope. Using 425M steel and sharpened with a guide on Spyderco's white ceramic stone of 1800 grit, this made 400 cuts. Before it started skating. Taking the same blade and sharpening it on a X-coarse DMT stone of 220grit it made 1450 cuts before it started skating and was reluctant to bite in and cut the rope. Either edge afterward could still manage to clip hairs off my arm. I also did several other steels with the same pattern emerging. DM
Click to expand...

The problem is you don't gain wear resistance in sharpening, it is a set property of the steel. Only by changing the geometry of the edge should you see such a large difference in cutting performance. I say this because while running over 150 cycles on a CATRA machine it only showed about a 3% difference between edges sharpened with a coarse stone (45 microns) and a fine stone (3 microns).
 
IIRC Catra testing uses an abrasive loaded substrate, not rope. I am not that familiar with it, are there multiple testing protocols in terms of type of cut it can perform and on different media?

In my own experience I witnessed a huge difference in longevity (all else being equal) depending on edge prep. Massive improvement in longevity when using a coarse edge for manually cutting coated papers at work, and likewise a tremendous improvement in edge retention using a polished edge for chopping - after making about a hundred cuts through Norway Maple branches up to 2" the edge fileted my pants leg when I wiped it lengthwise on my thigh - just the bit of swell at the belly of my bolo machete (right at the sweet spot) was enough to pull through the fabric. At 200 or 300 grit I don't think the edge could have done that with no use, let alone after making a bunch of hard cuts.

Am certainly not disputing any Catra testing, but by its nature, might not be capable of definitive results outside of the testing parameters.

Martin
 
The CATRA machine can use the silica impregnated paper, manila rope, and a few other things I can't remember right now. It applies a load and performs a set number of cut cycles recording the number of cards cut on each cycle showing a graph of edge sharpness loss. It's performs a consistent cut with a consistent pressure on a consistent media, this all adds up to consistent results which is hard to get in the backyard.
 
It's all really going to depend on the material being cut and how it's being cut as in draw vs push cutting.

For rope and other like material a coarser edge will continue to cut longer before it edge starts to lose bite and skate across the surface.

One has to adjust the edge finish for the material being cut and how the person does most of their cutting.

Like everything else in the knife world one has to give up one thing to get another.

A good balanced general purpose edge would be around 14-16 Microns or as an example the Spyderco Brown Stones, 400 to 600 Silicone Carbide stones or the 600 grit EP Stone...

The reason why Manila rope is used is because it's not easy to cut efficiently so if one has an edge that will go though rope easy in a draw cut it will also make for easy cutting on other media.
 
knifenut1013 said:
The problem is you don't gain wear resistance in sharpening, it is a set property of the steel. Only by changing the geometry of the edge should you see such a large difference in cutting performance. I say this because while running over 150 cycles on a CATRA machine it only showed about a 3% difference between edges sharpened with a coarse stone (45 microns) and a fine stone (3 microns).
Click to expand...

CATRA is machine testing and obviously the best method to do any kind of long term Testing.

3% on CATRA is HUGE by the way and to translate those results to hand testing on various methods it would make a rather large difference factoring in all of the variables....

In short it would be very noticeable by hand and the percentage of difference would be much larger..
 
do you have a link to any of the tests you are talking about? It would be an interesting read and I would like to see it.
 
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