Raising a burr without hitting the apex?

[bpeezer]

I recently purchased one of those Veho 400x digital microscopes, and I must say it's one of the most exciting tools in my sharpening toolbox. One of my edges wasn't quite as sharp as I was expecting, so I took a look at it under the microscope and discovered that I didn't quite hit the apex on one side of the edge. This was extra surprising because I made sure to raise a burr on both sides at first. Anyone have any idea how I could raise a burr on both sides without properly hitting the apex? Here's the image.

 

[Ernie1980]

I did not think that was possible

 

[Obsessed with Edges]

I recently purchased one of those Veho 400x digital microscopes, and I must say it's one of the most exciting tools in my sharpening toolbox. One of my edges wasn't quite as sharp as I was expecting, so I took a look at it under the microscope and discovered that I didn't quite hit the apex on one side of the edge. This was extra surprising because I made sure to raise a burr on both sides at first. Anyone have any idea how I could raise a burr on both sides without properly hitting the apex? Here's the image.

The underlined part of the bolded text above is the clue. It's possible to generate a burr from one side only, while the edge may still not be sharp. If the bevel on the other side of the edge isn't flat, or has another small (micro) bevel on it, you may not get a burr from that side at the same time (because the hone isn't yet contacting the actual edge apex), and the bevel may need more grinding (flattening) from that side. This is why it's important to make sure you form a new burr from BOTH sides, before assuming the edge is fully apexed and sharp. In other words, this is how you make sure you actually reach the apex from BOTH sides. A burr that's formed from only one side may get 'flipped' or bent either way, and can fool one into believing the burr has been generated from each side. When both bevels are completely ground to intersect flatly at the apex, the change in sharpness will be immediately apparent, and that's when a new burr will immediately begin to form from the side being ground.


David

 

[bpeezer]

The underlined part of the bolded text above is the clue. It's possible to generate a burr from one side only, while the edge may still not be sharp. If the bevel on the other side of the edge isn't flat, or has another small (micro) bevel on it, you may not get a burr from that side at the same time (because the hone isn't yet contacting the actual edge apex), and the bevel may need more grinding (flattening) from that side. This is why it's important to make sure you form a new burr from BOTH sides, before assuming the edge is fully apexed and sharp. In other words, this is how you make sure you actually reach the apex from BOTH sides. A burr that's formed from only one side may get 'flipped' or bent either way, and can fool one into believing the burr has been generated from each side. When both bevels are completely ground to intersect flatly at the apex, the change in sharpness will be immediately apparent, and that's when a new burr will immediately begin to form from the side being ground.


David

Thanks for the insight! Would you suggest deburring after getting the burr on one side so you know for sure that the burr on the other side is a new one?

 

[Obsessed with Edges]

Thanks for the insight! Would you suggest deburring after getting the burr on one side so you know for sure that the burr on the other side is a new one?

That's not a bad idea. Just make sure to do it cleanly, without creating any new asymmetry (like a new microbevel) in the process. Ideally, it's always best to go very lightly as you approach the apex, and watch very, very closely as you work, to catch newly-formed burrs as early as possible. Really big burrs are harder to scrub off without using the stone, and that introduces a new possibility of micro-bevelling or otherwise degrading good work done prior.

The best indicator you've done it right, is the obvious up-tick in sharpness when the edge becomes truly apexed. For me anyway, that's when the edge suddenly begins to really 'bite' into fingertips, when feeling the edge.


David

 

[jackknifeh]

At some point on at least one stroke you need to hit the apex to create a burr. If you know you haven't hit the apex and there is a burr on the opposite side it's a burr from a previous sharpening that wasn't removed.

My goal is to not create a burr, ever. That's my goal even though it's really impossible. But with my goal of NO burr I have to live with tiny, maybe even microscopic burrs As I'm getting the bevel closer and closer to the apex I slice paper. As soon as the apex is reached on both sides and creating as small a burr as possible the knife will be sharp and slice paper cleanly. So I'm testing the apex being reached by cutting, not by flopping some steel to the other side of the blade. All this steel is just wasted. Watching the bevel is the key. Using a marker helps but if you are using water or oil or a liquid that will wash the marker off. I use dry stones (DMT, ceramic) most of the time so the marker will stay on the edge making it easy to see when the apex is getting close. Watching the scratch pattern is good also but my eyes are getting older by the minute.

Absolutely no burr would require stroke and angle control at the perfect level and of course that's impossible. I just try to create as small a burr as I can with a goal of no burr at all. I just hate to waste the steel I paid for.

 

[Ben Dover]

Ink both edges before you start, and check the ink on the edge under a lighted loup often.

 

[OHALLUM]

If the bevel on the other side of the edge isn't flat, or has another small (micro) bevel on it, you may not get a burr from that side at the same time (because the hone isn't yet contacting the actual edge apex), and the bevel may need more grinding (flattening) from that side. This is why it's important to make sure you form a new burr from BOTH sides, before assuming the edge is fully apexed and sharp. In other words, this is how you make sure you actually reach the apex from BOTH sides. A burr that's formed from only one side may get 'flipped' or bent either way, and can fool one into believing the burr has been generated from each side. When both bevels are completely ground to intersect flatly at the apex, the change in sharpness will be immediately apparent, and that's when a new burr will immediately begin to form from the side being ground.
David

Thanks for that description and explanation David! I have often done that very thing, and was puzzled as to why my blade was not as sharp as I thought it should be. I have sometimes put it aside and come back the next day, and started all over again, only to have it magically get sharp the second time around. I tend to try to not over grind my blades and grind away unnecessary steel when searching for that ever important burr to show up.

Every once in a while (really pretty often) I will read something on this forum, and this big blinding light bulb will light up in my tiny brain cavity, and I will have an "ah ha" moment such as this. "Ah ha, so that is why I can't get X to happen for me, I need to do Y with my Z in order to accomplish my goal. Most answers are available here if you seek them out with an open mind. There is a wealth of good information on here from the many knowledgeable people that frequent this forum, and for that I am thankful.

Blessings,

Omar

 

[BluntCut MetalWorks]

Most likely non-apexed reason as pointed out by David - burr 'flipped' over. Or

From the image, I see (hopefully not cause by my sleepy 4 eyes) flat top/apex. So really burrs did occurred on both sides, which could had been created by excess pressure - deduced from scratch pattern/depth. Either reduce pressure. Or use exclusive edge-leading stroke to test if it is the case. It is when burrs not readily show up.

When in doubt - just to use your microscope to incremental check after a few strokes to see what's going on.

 

[Chris "Anagarika"]

Another good thread that should go into my sharpening thread 'collection'. Thanks for the question and insight!

 

[bpeezer]

Most likely non-apexed reason as pointed out by David - burr 'flipped' over. Or

From the image, I see (hopefully not cause by my sleepy 4 eyes) flat top/apex. So really burrs did occurred on both sides, which could had been created by excess pressure - deduced from scratch pattern/depth. Either reduce pressure. Or use exclusive edge-leading stroke to test if it is the case. It is when burrs not readily show up.

When in doubt - just to use your microscope to incremental check after a few strokes to see what's going on.

The edge looks perfectly fine on the other side, that's why I wasn't sure if it was a flat apex or more like an accidental microbevel on just one side. The knife is still fairly sharp, it has no problem slicing newspaper and push cutting receipt paper. Also, you mentioned scratch pattern depth. Do you by any chance happen to have an image of how an edge should look under 400x magnification? It's great that I can see what's going on, but I don't know how to interpret 90% of what I see.

 

[Jason B.]

A burr will form from grinding and reaching the end of a plane, you don't need to apex two planes to form a burr. The first time I noticed something like this happen was when I started using a belt grinder where the burr tends to be much larger. Like bpeezer, a microscope showed me it can happen with hand sharpening too.

It's the reason I do not advocate only watching for a burr, it can be misleading at times.

 

[Obsessed with Edges]

A burr will form from grinding and reaching the end of a plane, you don't need to apex two planes to form a burr. The first time I noticed something like this happen was when I started using a belt grinder where the burr tends to be much larger. Like bpeezer, a microscope showed me it can happen with hand sharpening too.

It's the reason I do not advocate only watching for a burr, it can be misleading at times.

That's almost a textbook description of the factory edges often seen on Case's stainless blades (Tru-Sharp/420HC). Case uses a very quick & aggressive pass on belts to apply the working edge to their blades (edge-leading sharpening). Occasionally, some big burrs are even found on the shoulders of the bevels. I have a lot of the Case Tru-Sharp blades, and oftentimes they come out of the box with some huge & thick burrs on them, sitting atop an 'apex' that's often round, thick or otherwise blunt. Those are the knives that instigated my 'obsession' with cleaning up burrs in the first place (and re-bevelling almost every new knife I buy).


David