The Sharpening Thread

Sure you can push cut with a toothy edge, but it does take more force than with a polished edge. I like to whittle wood, so a polished edge is what works for me in my fixed blades. In my folders, where I'm going to cut abrasive materials daily, I will keep, I'm not sure what grit, a well worn in red DMT fine stone finish on it. I think we can all agree that toothy edges excel at slicing and polished ones do better with push cutting. Some of us like to try and find that middle ground in between the two. This kinda gives you the best of both worlds in push cutting and draw cutting. Different steels will also have different "middle grounds".

 

Exactly! I like the saw blade analogy. Hand saws are the same way. Less teeth per inch for the harder stuff and more teeth per inch for the soft greenies.

My fixed blades stay polished for 90% wood work. Folders, depending on steel, I try and find that middle ground for cutting dusty cardboad, rubber hoses, plastics, boxes, just about anything I need to cut, all in a dirty foundry environment. I realized that highly polishing all of my folders tended to dull faster. I do have knives in steels that are an exception to that rule though.

I believe we're all just saying the same thing in different ways that we see it!

 

You're right. I hate grit as an abrasive measurement for precisely that reason. I rarely use them, but I was writing without a reference and I don't know them by heart. It is a 12000 micromesh @ 2µm.

I'm well familiar with the site and the images. I understand that the pictures show those waveforms on that steel. I personally think that it could be a result of the steel structure and the forces exerted by the abrasives on that structure. I doubt all steels would behave by exhibiting the same waveforms. At any rate, those pictures do very little to demonstrate longevity of blade edge as a function of waveform or edge finish. The coarsest example is 1K and we don't know what the material looked like before the abrasive was applied. It is possible that the wave structure was present prior to the 1K abrasive. That's not really what Todd was going for anyway I think.

If you want great sawing action you need teeth. Different teeth for different materials. Agreed.

I don't have enough experience to weigh in on which edge is best for each material with any finality, but I doubt it is so clear cut. Scalpels are well polished edges for the ultimate in cutting flesh. The rigidity of the material and how the material is held play as large a role in whether a push or slicing cut is more effective as the apex itself. I suppose my main dislike for a toothy edge is when I am cutting something that is not held fast the coarse edge wants to grab the material and pull it rather than cutting it. If the subject of my cut is against a surface or held fast away from a tether, then usually a push cut is a better fit. For this reason, I tend to like push cuts better than sliding cuts.

Maybe I need to search some more but I have yet to see any coarse vs fine cutting test with enough proper scientific method to render it valid much less the microscopic look at what is happening at the blades edge. My own experience yields more performance and longer use from a refined edge than a coarse edge but there are too many variables to come to any kind of large scale conclusion. I may also find a blade is not suitable for the task before it is unable to perform the task.

I suppose in the end it is important to differentiate keen and sharp and that a coarse edge can be sharp enough to handle most jobs with a slightly wider apex making it last longer even if it isn't actually as keen as a refined edge. When we compare a wider apex with a finer apex, longevity in the presence of abrasive wear does play a role since there is only so much metal to abrade at the apex. If I only cut cardboard all the time I would likely see a larger difference. Cardboard is an abrasive standout though and very few materials cause the same kind of abrasion.

 

They also use scalpels on cadavers. Flesh is elastic and pulling it around instead of cutting it is not always wanted. It's true that scalpels do dull quickly because of their ultra thin profile, though for cadavers we would generally use a scalpel for maybe 50 cuts many times the length of the blade edge before there was any desire to switch.

The article you linked to the science of sharp shows that the same apex width is NOT achieved with an under 4K Shapton glass stone. And this is a great example of why it's so difficult to compare the different finishes, especially when they are done freehand. More stones means more opportunity to damage the edge instead of refining it.

In Cliff's article we have to assume that there are no errors in sharpening with the various grits. I saw only 2-3 pics of the edges produced. Not to say that they aren't all done with finite precision in a minimal error scenario though the main bevel tolerance accuracy is given at 4 degrees inclusive with is very relevant when the entire range is 12-16 inclusive that's up to a 33% increase between edges. The stones are also from various parts of their life cycles. At any rate I do think the results are obvious enough to show that coarse edges are better for slicing longevity. The article also goes on to say that the refined edges are often better for pushcutting in both initial performance and push cut longevity and that some of the course edges would not perform pushcuts at all. Since they are for different applications it becomes futile to attempt to compare them directly. And therein is your point I suppose. I did think that the longevity would be better for refined edges than his experiment shows, but I would have performed push cuts with the polished edge and not slicing cuts. It's unreasonable to accept that an edge used other than in its intended purpose would fare well over extended use. The source of the Manila rope and its state are also very important as a used and dirty rope would likely favor the coarse edge far more than a clean, non-abrasive Manila rope.

It's not often that the materials I cut are made abrasive by dirt with the exception of the outside of downed wood. If yours are I can accept that it makes your choice easier, but I'm not convinced that the cause is the waveform you talk about given the science of sharp findings/measurements. The pleasure I get from "touch cuts" where only an imperceptible amount of force is required to divide the items I encounter daily likewise explains my preference. The lack of effort required means less work done by the edge and inherently an increase in longevity by use in that manner as a result.

At any rate I'm more tempted to play with some coarse edges now to see if I can get a better feel for them. I just have to find a use for one first.

 

Coarse edges mean different things to different people. To me a fine edge is 1200 grit. I'm unfamiliar with how the ansi grit system works, so I only have DMT stones to reference to. Green DMT 1200 grit, is a fine edge to me. Finish it with some stropping and it's what I consider a polished edge. But to others, green DMT 1200 grit is considered coarse, especially if they finish with 6K,10K, even 30K grits. I don't see the advantage of polishing an edge to that high of a grit. Edges that thin at the apex can't be very durable. I would expect some kind of chipping on a microscopic level, where the carbides are being abraded away. Sharp is sharp, and dull is dull. As long as we can get our knives to cut to our satisfaction, it's all that matters!

 

I enjoy a good discussion of sharpening and what constitutes sharp.

 

Thanks for all the time you've spent on these replies. I really appreciate the conversation.

To anyone reading who has adequate experience in both knowledgeable sharpening and game processing, what kind of finish have you seen the best balance of performance and durability from? Unfortunately the knife coming to me for a overhaul is an unknown steel but I will get a good feel for how hard or soft if it as I start sharpening it and will adjust the angle accordingly. Durability will be at least as important as initial performance.

I understand that theoretically a burr may not be formed if the metal removal stops exactly when the edge is apexed, but rarely is the entire length of the edge apexed on the same stroke, and the result is a burr on most steels, especially at course abrasive levels. Removal of the burr is not an issue. Adding a micro bevel is also not an issue. The knife is a BRK, and will have a convex grind stock. I plan to keep it convex so adding a convex micro bevel would very slightly blunt the edge but shouldn't make a large detriment to the cutting performance given the already set main bevel angle.

 

This is my personal opinion and may not reflect the attitude of professionals. For game processing, I prefer an angle of 18 to 20 dps. Stones of @ 800 to 1000 grit leave what I consider to be an adequate toothiness on the apex. This should be slightly convex and polished using black BRKT compound followed by the green. This edge will skin and cut well in game processing. The edge can be touched up easily with some light stropping. Just don't over do it.

 

#alledgesmatter

 

Except for dull ones....

 

Which came first, the dull edge or the sharp edge?

Or, the knife or the sharpener?