Burr = getting sharper?

[DavidL41]

I have been sharpening my knife with the same grit stone around 1k and I can't seem to tell if the knife is getting sharper or not only using that one stone. There is a burr every time I use it. Does that mean every time I use the 1k japanese standard it will slowly get sharper because theres always a burr forming when I sharpen. Or does the sharpness peak at a certain level and thats the cap for that stone and the next sharpening with the same stone takes it up to that cap?

Side note: what equivalent grit in Japanese standard is it needed to get my knife as sharp as a scalpel or sharp olfa utility knife. With the olfa I can do the "paper sharpness test" with a piece of semi-stiff leather and slice through it like it is a piece of paper.

Seems like the 5 dollar olfa knife beats my 154cm steel knife (was made for leather) for pull cutting leather because of its thin blade and also because the 154cm slowly changed into a recurve - it was a curved blade sharpened on a flat stone. Would it be worth while do you think to invest in better stones to try to compete with the olfa?

 

[Tim the Wizard]

As you sharpen one side, a burr will appear on the opposite side of the blade. Once a moderate and consistent burr can be felt, flip the blade to the opposite side, and sharpen until the second burr forms. Then, knock the second burr off with one one or two very light passes, or by using a ceramic hone and a strop.

Perceived sharpness is a function of bevel angle and polish. The more acute the angle, the sharper the blade will be. The finer the polish, the smoother the blade will cut. Many prefer a less polished, toothier bevel at a lower grit depending on the task at hand.

If 1000 is the maximum grit you intend to work with, then forming more burrs than necessary will only waste metal, and over time will lessen the sharpness by increasing the bevel angle to be more obtuse as you wear away at the secondary bevel behind the primary edge bevel. In this case I am using primary bevel to refer to the cutting edge. Others will use the term secondary bevel to refer to the cutting edge. Once the burr is formed on one side and then the other, in my opinion, there is little point in continuing to knock the burr from side to side unless you do so with a higher grit stone.

If you wish to get a sharper knife, then try to sharpen at a more acute (lower) angle. Likely, this will not be possible unless you first remove metal on the secondary bevel behind the edge. For example, if I have a knife sharpened with a 21 degree bevel (42 inclusive) and I want to move to a 19 degree bevel (38 inclusive), I will first have to sharpen at 15 or so degrees and establish a secondary bevel while wearing away the obtuse primary edge bevel. Once the secondary bevel has been established, I can then easily sharpen at 19 degrees on the primary bevel.

In summary, if you are forming burrs, the only way you will enhance the perceived sharpness of the blade is to

1. remove the burr

2. sharpen at a lower angle

3. polish to a higher grit

 

[Bo T]

If I understand you, I think the first step is getting rid of the burr. Try a gentle hone on some fabric. You might catch the burr and pull it off.

 

[DavidL41]

Thanks very helpful.

When I get into 5k, 8k or higher how sharp is what I have now with 1k. Is 1k getting the blade only 60 percent sharp and 5k/8k getting the blade nearly 100 percent potential?

The 1k doesnt get the blade too sharp which may be an error on my part. It can cut paper, just not effortlessly.

 

[Jason B.]

A blade is sharp when it's sharp, the grit you finish at determine how refined the sharpness is.

 

[HeavyHanded]

There is no objective measure of sharpness, no percentage that can be measured. Sharp is a clean a cutting edge. The grit value (in combination with stone composition and steel type) determines how much variation in uniformity across and/or along the edge, the high points (properly done) are all sub micron. The construction of materials to be cut, and the manner to be cut, will determine what edge finish will work best for a given task. In general, finish strategies that cut with the least amount of force applied to the cutting edge will give the best longevity.

Thin stock on the cheaper knife is likely contributing to its better performance - thin the 154cm, not just the cutting edge, but the entire stock thickness, and it should cut very well. That said, in my experience, good quality high carbon steel with no notable amounts of carbides will take and hold a fine edge for a long time, as long or longer than the carbide rich steels under most applications. It also is far easier to touch up at the finer polish. Your saga continues - just because you had good luck with one 154cm blade doesn't mean its the best choice for your job. Believe the results you are getting - if the cheaper carbon steel olfa knife is the better choice in use, use it or make the 154cm match its physical dimensions as best you can and see if it doesn't work better.