removing a back bevel

[Woodmonkey]

There must be some paint somewhere that needs watching drying

 

[Phil Pascoe]

...or boards warping...

 

[MIGNAL]

Give me some logic guys. If you dislike these threads so much, why on earth do you continue to read them?

 

[Phil Pascoe]

In the vain hope that we might actually learn something.

 

[Jacob]

Which bit don't you understand?

 

[bugbear]

.....
swarf. But if it isn't removed, merely moved, you get a burr. The burr
(obviously?) extends beyond the original shape of the tool, so metal must have been moved.......

I thought I'd join in the waffly burr burbling.
The burr isn't metal which has been moved - it's just been left behind. As the honed edge approaches 5 in BB's drawing, the metal left between 4 and 5 is thin enough to be pushed out of the way rather than honed off. This is really noticeable with some laminated blades where the harder steel of the face can remain as quite a wide but very thin foil, bending upwards as the softer bevel behind it is removed. A bit like grating an apple - the soft insides get grated but bits of peel lift away and remains as a flap still attached (sometimes).

Reasonable and temptingly plausible, but I don't think it's true.

If that were the case, the size of the burr would be (pretty much) the distance removed
during sharpening (which is tiny), and it's evident they're bigger than that.

BugBear

 

[Jacob]

.....
swarf. But if it isn't removed, merely moved, you get a burr. The burr
(obviously?) extends beyond the original shape of the tool, so metal must have been moved.......

I thought I'd join in the waffly burr burbling.
The burr isn't metal which has been moved - it's just been left behind. As the honed edge approaches 5 in BB's drawing, the metal left between 4 and 5 is thin enough to be pushed out of the way rather than honed off. This is really noticeable with some laminated blades where the harder steel of the face can remain as quite a wide but very thin foil, bending upwards as the softer bevel behind it is removed. A bit like grating an apple - the soft insides get grated but bits of peel lift away and remains as a flap still attached (sometimes).

Reasonable and temptingly plausible, but I don't think it's true.

If that were the case, the size of the burr would be (pretty much) the distance removed
during sharpening (which is tiny), and it's evident they're bigger than that.

BugBear

You need to look at things more closely. You can see it clearly, especially with some blades - Stanley 5001 amongst others.
I highly recommend "looking at things" as a way of finding out about them. Often neglected in all the theorising.

 

[Phil Pascoe]

Which bit don't you understand?

I understand all of it. Just as I understood it last time. And the time before. And the time before that. Every sensible or innocent question about sharpening n amount of pages later ends like this.

 

[bugbear]

I highly recommend "looking at things" as a way of finding out about them.

Take a simple bar of metal and file the end. If you look you'll see a nice big burr extending well beyond
the orignal profile of the bar. It hasn't been "left behind". It's been moved.

BugBear

 

[Jacob]

Which bit don't you understand?

I understand all of it. Just as I understood it last time. And the time before. And the time before that. Every sensible or innocent question about sharpening n amount of pages later ends like this.

Why not go and find a more interesting thread? Currently there's a fascinating one about cleaning old hinges. Might be more to your taste, something you could get to grips with?

 

[Corneel]

The thread would be half as long without the guys complaining about the length of the thread. Like Mignal sais, if you don't like it, read something else.

Grit removes metal in several ways, depending on the shape of the individual grit particle. It can cut the metal, like a toolbit, but it can also smear the metal, plowing through the surface. The latter creates a wall of metal ahead of the groove it plows. I imagine that is part of the burr, but of course I don't really know.

Why does the burr disapear, mostly, when you switch to a polishing stone? I guess you polish through the root of the burr, so it cuts lose. At the same time you create a new very fine burr, which you can't feel anymore.

 

[Jacob]

If the burr was formed by metal being "moved" it'd be behind the heel of the bevel, not in front at the edge (assuming you are sharpening in the normal forwards way).
The burr is metal left behind as the thinning edge bends away - differently with different metals. You can see it if you look. Try it with a Stanley 5001. Others similarly, depending on how tough/springy the steel is.

 

[bugbear]

If the burr was formed by metal being "moved" it'd be behind the heel of the bevel, not in front at the edge (assuming you are sharpening in the normal forwards way).

I think it's usual to sharpen with a back and forth motion - I don't think any body lifts on the back stroke.

BugBear

 

[Corneel]

There you've got a point. I've never looked for a burr at the heel of the bevel. I move the iron back and forth on the stone, so you would expect a burr on both sides. Unless it is indeed like you say.

So that means, when the burr is raised you are not quite there yet. But that would be taken care of with the polishing step of honing.

At the other hand, when you are filing or sanding a square bit of steel, you also get a burr.

I just went out to the shop. Indeed, no burrs on the heels of any of my tools, chisels or planes. But the angle is so wide, about 150 degrees usually, that a burr is unlikely to form.

 

[Jacob]

If the burr was formed by metal being "moved" it'd be behind the heel of the bevel, not in front at the edge (assuming you are sharpening in the normal forwards way).

I think it's usual to sharpen with a back and forth motion - I don't think any body lifts on the back stroke.

BugBear

Normal freehand sharpening all the force is in the forwards thrust with the edge only briefly in contact with the stone, as you dip the handle. Followed by a gentle back stroke, if at all. There is no way metal could find its way forwards to hang off the edge.

 

[woodbrains]

Normal freehand sharpening all the force is in the forwards thrust with the edge only briefly in contact with the stone, as you dip the handle. Followed by a gentle back stroke, if at all. There is no way metal could find its way forwards to hang off the edge.

Hello,

Wow, just dipped in to see if anything interesting was being posted and found another sharpening debate. Nice to see nothing has changed (hammer)

Are you identifying yet another inefficiency with your sharpening technique, Jacob? Arm flapping just allows the bit of the blade you want sharp contact the stone a tiny percentage of the stroke anyway, but now you are saying you don't do anything at all on the back stroke. Most sharpeners, jig or otherwise use both forward and backward strokes to sharpen, doubling efficiency. Try it, you might find things go quicker.

Burrs will form from moving forwards only on the stone. And it is a movement of metal, this is nothing new, it has been observed as long as people have abraded metal. If the physics as to how things can be moved forwards on this way eludes you, don't argue the point. It demonstrably does happen if you just look.

Mike.

 

[Corneel]

But what is a burr?

Is it a deformation, like in this picture?

Or is it because of the plowing effect of the grit particles? In other words, is it the material removed?

 

[bugbear]

I just went out to the shop. Indeed, no burrs on the heels of any of my tools, chisels or planes. But the angle is so wide, about 150 degrees usually, that a burr is unlikely to form.

Yes - the angle precludes it, I think.

BugBear

 

[Jacob]

....

Burrs will form from moving forwards only on the stone. And it is a movement of metal, this is nothing new, it has been observed as long as people have abraded metal. If the physics as to how things can be moved forwards on this way eludes you, don't argue the point. It demonstrably does happen if you just look.

Mike.

Burrs will form but not from metal moving against the direction of the grinding action. That is impossible and doesn't happen. If you bother to look closely you can actually SEE what happens, but idle theorising is obviously preferred, as ever. :roll:
The new sharpening is very "Alice through the Looking Glass" which is why all these threads go on and on I suppose.

 

[Jacob]

But what is a burr?

Is it a deformation, like in this picture?

Or is it because of the plowing effect of the grit particles? In other words, is it the material removed?

This diagram doesn't seem to have anything to do with sharpening. I think it's just a tease! :lol: