when do you need a burr, when do you not?

[bdmicarta]

All sharpening discussions tell you to raise a burr, then work the burr off. I always assumed that the reason for the burr was so you knew beyond a doubt that you had apex'd the edge. Well if you could stop exactly when you reached the apex you wouldn't raise a burr and you wouldn't need one. (Granted a user blade would have varying amounts of dull along the edge and you would not be able to apex the edge everywhere at the same time.)

But what always hangs me up is that I wonder how the factories do it- they take blades out of the stonewash tank or whatever, make a quick pass over the belt sander with both sides of the blade, and call it good. They don't try to raise a burr, they don't bother to check for a burr, and they certainly don't take time to work the burr off. So in their quick pass over the belt sander do they even raise a burr? Do they raise a burr on one side and then quickly take it off when they sand the other side of the blade?

 

[fervens]

I think it depends on the manufacturer. I have seen brand new knives that weren't apexed and ones that still had a burr. Some companies will go over a leather belt at the end or a buffing wheel and strop the edge so if there was a burr, it would be gone after that over stropping.

A burr will form when two planes meet as far as i know. At my skill level (not that high), i can't hit the apex and not form a burr. I have heard some people claim to be able to do this though. If you take your time and know when you switch to single passes per side and light pressure, you can keep from forming a noticeable burr that stropping can take care of quickly. It is unnecessary to form a "big" burr though. Most are taught to do this in the beginning cause it's a fairly fool proof way of knowing when you have hit the apex.

 

[OHALLUM]

When I first got my Opinel #6 in carbone, the burr was still on the blade. A quick buff on my slotted paper wheel and you could "split" hairs with it. My #8 in stainless was the same way, only it took a little more work to remove the burr. No grinding needed, just stropping to remove the burr. I think raising a burr is a necessity to achieve a good sharp blade. Just how much of a burr you raise, depends on your level of expertise. I am still at the stage that I need one that I can feel with my fingertips, to assure that I have reached the apex. There is not a lot of metal removal difference in a fine burr along the full length of the edge, and a minute burr that you can't feel, but could see under magnification.
My procedure is to grind a full thin burr the first time to be sure, than to have to re-grind again because the apex was not reached. Works for me, YMMV.

Blessings,

Omar

 

[Jason B.]

All sharpening discussions tell you to raise a burr, then work the burr off. I always assumed that the reason for the burr was so you knew beyond a doubt that you had apex'd the edge. Well if you could stop exactly when you reached the apex you wouldn't raise a burr and you wouldn't need one. (Granted a user blade would have varying amounts of dull along the edge and you would not be able to apex the edge everywhere at the same time.)

But what always hangs me up is that I wonder how the factories do it- they take blades out of the stonewash tank or whatever, make a quick pass over the belt sander with both sides of the blade, and call it good. They don't try to raise a burr, they don't bother to check for a burr, and they certainly don't take time to work the burr off. So in their quick pass over the belt sander do they even raise a burr? Do they raise a burr on one side and then quickly take it off when they sand the other side of the blade?

Factory grinding on a belt sanders is always followed by a de-burring process, otherwise you would not get a Sharp knife. Power equipment forms the largest of burrs and are much different from those created during hand sharpening. They are very easy to move around like foil at the end of the edge.


The theory of stopping right when the apex forms without ever forming a burr is just something we dream of.

 

[David Martin]

When I first got my Opinel #6 in carbone, the burr was still on the blade. A quick buff on my slotted paper wheel and you could "split" hairs with it. My #8 in stainless was the same way, only it took a little more work to remove the burr. No grinding needed, just stropping to remove the burr. I think raising a burr is a necessity to achieve a good sharp blade. Just how much of a burr you raise, depends on your level of expertise. I am still at the stage that I need one that I can feel with my fingertips, to assure that I have reached the apex. There is not a lot of metal removal difference in a fine burr along the full length of the edge, and a minute burr that you can't feel, but could see under magnification.
My procedure is to grind a full thin burr the first time to be sure, than to have to re-grind again because the apex was not reached. Works for me, YMMV.

Blessings,

Omar

I like this info.^. It surprises me that people who have never been to a knife manf. plant and watched the process, all of a sudden know how blades are done. DM

 

[phillipsted]

If you are sharpening all the way to the apex, then you will be raising a burr almost by definition (like fervens mentions above). It may be a small, thin burr, or it may be a huge ragged chippy burr. You may or may not be able to feel it with your finger - but it will still be there...

The trick is to raise a burr that is so tiny that removing it does not damage the steel along the apex. If you really grind on your stones with a lot of force, you'll create a big hairy burr that you can feel with your fingers. When this burr gets stropped off, it will tend to break off part of the edge with it (depending on the stropping technique, steel, etc. etc.). That, obviously, isn't good.

TedP