Wasted Steel

[Cheshirechappie]

I think that post pretty well accords with what everybody else has said, though I'm not sure everybody excluded honing at 30 degrees from their computations.

There's one point I'd beg to differ on. From experience, I know it's perfectly possible to freehand hone and maintain a 30 degree secondary (working edge) bevel accurately enough for all woodworking purposes. Developing that skill takes a little practice, but once you've 'got it' it's ingrained for life. I fully accept that some people prefer to use a honing guide for any number of reasons, and that's fine - do whatever works for you - but to suggest that only a honing guide will keep the angle is bunkum - craftsmen have been 'keeping the angle' freehand for generations. Many still do.

 

[MIGNAL]

I freehand the secondary angle. I tend to use very short forward/backward strokes on a very fine stone. My theory states that the greater the arm movement the more chance there is of 'losing' the angle. The figure of 8 seems to be an incredibly complicated form of arm movement, although I've no doubt that some people master it.
I've no idea how accurate I am with that secondary bevel, at least I don't pay much attention to whether I lose it or not. I simply observe how large the secondary bevel is. I only get 3 or 4 'sharpenings' before I redress the primary bevel but that's not because I'm losing the angle. It's more about having to remove less metal.

 

[woodbrains]

Hello,

The geometry just over complicates the issue. As Bridger posted, we need to hone past the wear on the flat side of the tool to achieve sharpness and this requires the same amount of loss of length to the tool no matter what method of honing is used or what angle the bevel is at.

Being a bit controversial here, but the quickest way, with less steel lost to hone past the wear on the flat side, is to use a back bevel, or ruler trick! (hammer) sorry!

Mike.

Edit, no use for chisels, though just plane irons.

 

[G S Haydon]

Thanks for the diagrams Derek. Diagram 2 shows the black line of the grind angle projecting beyond the red first hone. If when we grind we leave in a sliver of hone both methods changes the length by the same amount. I think these diagrams only work if you grind to a burr so to speak?

As mike siad "we need to hone past the wear on the flat side of the tool to achieve sharpness and this requires the same amount of loss of length to the tool no matter what method of honing is used or what angle the bevel is at."

 

[Corneel]

All geometry aside, let's have a look at how much steel you need to remove to get beyond all the wear and tear from the edge. I have no idea how a chisel wears. i guess it totally depends on how it is used and a paring chisel has a different wear pattern compared to a mortise chisel.

So let's have a look at a plane blade's edge. The typical idea of the symetrical rounded tip after use is not correct. This is how a worn plane blade which didn't fail through bending or cracking looks like:

The wear on the bottom is from the steel rubbing over the wood. It forms a bulge which needs to be removed, otherwise this reduces the clearance angle too much and makes for a harsh ride. The wear at the top is from the shaving gliding over the steel. It is much longer, often very visible as a gleaming line on the face side of the blade (in a bevel down plane). This wear bevel doesn't need to be removed completely. It doesn't harm the working of the plane and it is allready fairly polished. So no need for a ruler trick in a bevel down plane.

So, to get practical, how do we know that we removed enough material from the bevel to get past the bulge on the bottom side of the blade? I think the best way to know that you removed enough is raising a burr along the full with of the blade. And then remove that burr in as clean a way as possible.

I used to sharpen on waterstones and I can't feel any burr when using my 8000 grit waterstone. So I would grind on a 1000 stone at 25 degrees or so untill I got a burr. Then raise the blade about 5 degrees and remove that burr with the 8000 grit stone. In regards to steel removal that must have been the method that wastes the most. Completely removing the secondairy bevel on each honing! Nowadays I use oilstones and I can feel the burr from a translucent Arkansas. I can also feel how it is removed with carefull attention to both sides, flipping the blade up and down. A strop completes this action and removes the last tiny bits. No need to go back to the coarser stones all the time, so not waisting that "much" material.

 

[woodbrains]

Hello,

From Corneel's diagram, it can be seen why a back bevel would remove less metal to reach the point of true sharpness. Also, a burr will be raised at the junction of the upper surface and clearance surface (as referred to in the diagram) in other words, at the apex of the wear. This is not the point of sharpness however, and relying on the burr as an indicator as when to stop honing is a red herring. We have to work on the sharpening bevel for a fair bit longer after the burr is raised. Corneel's mitigates this somewhat by stropping, which is essentially producing a back bevel. I wonder whether reverting to oilstones for a burr raising indicator is not a backward step. A burr is felt because the sharpening medium is coarser, so the tool not as sharp, though obviously stropping fixes that. It is better to see when an edge is sharp. I often feel a wire edge form, back it off on the stone and look for sharpness. If the wire edge is only just formed, I usually see that the edge is not sharp. It is not difficult, in good light, to be able to see the wear bevel on the back has still remained, even if the burr was raised and removed. Of course I'm only talking minutiae here, and whether the difference is worth worrying about is down to the individual woodworker. But for the sake of this discussion, the wear bevel on the flat side must be removed for true sharpness and this is not the point the burr is raised.

Mike.

 

[Trafalgar]

I think that post pretty well accords with what everybody else has said, though I'm not sure everybody excluded honing at 30 degrees from their computations.

There's one point I'd beg to differ on. From experience, I know it's perfectly possible to freehand hone and maintain a 30 degree secondary (working edge) bevel accurately enough for all woodworking purposes. Developing that skill takes a little practice, but once you've 'got it' it's ingrained for life. I fully accept that some people prefer to use a honing guide for any number of reasons, and that's fine - do whatever works for you - but to suggest that only a honing guide will keep the angle is bunkum - craftsmen have been 'keeping the angle' freehand for generations. Many still do.

Those who hone secondary bevels can simply drop down occasionally and hone on the grind to manage the size and angle growth of the secondary. There's no real overriding reason to develop an innate sense of 30* though this may be a result over time.

I've taken to grinding more often to keep the hollow lookin' good. Takes mere seconds.

On plane irons, I use Jacob's rounded under method which is the fastest and easiest to maintain of all.

 

[lurker]

This has to be a truly original sharpening debate, I don't recall one like it before!

Maybe, but it looks like a discussion about the bleedin' obvious to me

 

[Corneel]

Hello,

From Corneel's diagram, it can be seen why a back bevel would remove less metal to reach the point of true sharpness. Also, a burr will be raised at the junction of the upper surface and clearance surface (as referred to in the diagram) in other words, at the apex of the wear. This is not the point of sharpness however, and relying on the burr as an indicator as when to stop honing is a red herring. We have to work on the sharpening bevel for a fair bit longer after the burr is raised.

But, what more do you want? The shavings have polished the surface, there are no nicks or scratches, and the non flat shape doesn't interfere with planing. Sounds pretty ideal to me.
(In a bevel DOWN plane! Bevel ups and chisels follow their own rules).

I wonder whether reverting to oilstones for a burr raising indicator is not a backward step. A burr is felt because the sharpening medium is coarser, so the tool not as sharp, though obviously stropping fixes that.

An oilstone works very differently from a waterstone or sandpaper. The particle size is not very relevant to how an oilstone works. It mamages to creates large burrs because it somehow works "smoother". I think it pushes the steel around more then cutting it, which helps in burr formation. But you can get remarkably sharp edges from a worked in Arkansas stone, despite its rather coarse grit.

It is better to see when an edge is sharp. I often feel a wire edge form, back it off on the stone and look for sharpness. If the wire edge is only just formed, I usually see that the edge is not sharp. It is not difficult, in good light, to be able to see the wear bevel on the back has still remained, even if the burr was raised and removed. Of course I'm only talking minutiae here, and whether the difference is worth worrying about is down to the individual woodworker. But for the sake of this discussion, the wear bevel on the flat side must be removed for true sharpness and this is not the point the burr is raised.

Mike.

I agree totally about this being minutiae.

 

[Corneel]

To give an idea about what we are looking at. I took my Record 05 from the drawer. It really needs to be sharpened again, but it made a good case for some microscopy. My microscope has 470 times magnification.

First picture is the face side of the edge. You can clearly see the wear, that is the whitish area just behind the edge. Somewhat lower down you can still see some scratches from the last polishing efforts.



For comparison an image from the bevel side. It is hard to get things in focus on a slanted surface like this, but I focussed on the edge a much as possible. The first black stripe is the wear bevel, the convex shape that limits the clearance angle. As you can see it is much shorter then the wear on the faceside. Lower down you see my last sharpening efforts. The whitish stripe just below the black one is the 8000 grit micro bevel. Lower down you see much coarser scratches probably from a 1000 stone (very out of focus).



As you can see, the wear bevel on the face side doesn't look any worse then the microbevel on the bevel side that was polished on a 8000 stone.

 

[woodbrains]

As you can see, the wear bevel on the face side doesn't look any worse then the microbevel on the bevel side that was polished on a 8000 stone.

Hello,

Do you not think so? It looks vastly superior to me. The scratch pattern in the back bevel is considerably finer than that of the wear bevel. Think of it another way, if the wear bevel was no different to a honed bevel, then our tools would never get dull!

In any case, I'm not concerned in how you sharpen, but in the interest of this topic, honing to a wire edge is not the point to stop, but until the wear bevel is removed. The OP contended that no matter how we sharpen, the same amount of metal must be removed to get to that point, and I think we must agree. However, a back bevel WILL save metal, as can be clearly extrapolated from your graphic representation on the worn blade. I'm not saying this is what we should do, but it is the only way I can think of where achieving true sharpness removes less metal.

Don't forget, I started a thread precisely about the action of oilstones consolidating metal and achieving finer results than expected, for particle size. I don't remember getting much support for the idea then, what has changed?

Mike.

 

[Corneel]

I must say, it is very hard to draw conclusions from these kinds of pictures. You really need a SEM to see it well. The wear on the face side looks very smooth to me in this picture, about the same surface roughness as the 8000 grit microbevel in the other picture. You certainly can't see scratches on this picture in that wear area on the face side. Another clue is when you look at it on macro scale. You see a gleaming line, which means that the shavings have polished the surface.

And the edge becoming dull has another source then the surface quality of the faces. It is because of the very tip of the edge which becomes rounded. Add to that the loss of clearance in a plane which is another important aspect of dulling.

Polishing the faces of the bevel isn't the most important part of sharpening other then making them smooth enough to avoid craters in the edge. But when they are allready smooth, you don't need to smooth them again. So that kind of negates the need of a backbevel for this.

BTW, I don't remember that thread about oilstones? But I think I agree with you in that respect.

 

[Corneel]

It looks like I am not alone with this opinion. While searching for something else, I happened upon this quote from Brent Beach' website. Brent Beach is the guy who did a lot of blade testing years ago and who made a lot of hoopla around backbevels, argumenting that you can't get a really sharp edge without a back bevel. But then he writes on a page about bevel up planes (http://www3.telus.net/BrentBeach/Sharpen/bevel up.html):

Conventional sharpening techniques handle the conventional problem: the problem of sharpening a bevel down iron. Conventional sharpening techniques concentrate on the bevel side of the iron. Conventional sharpening techniques do a good job on the bevel side, do little on the back face, but this works out pretty well for bevel down planes. The back face of the iron gets the upper wear bevel, which is slightly rougher than a well honed bevel and is at a slightly greater angle than expected. The net effect of not working the back face of the blade is a slight increase in effort, with little decrease in surface quality except perhaps for soft and stringy woods (where the increased effective planing angle is a negative).

That does contradict with his opinions about backbevels a bit, doesn't it? Of course, when you are into sharpening with sub micron abrassives, you can get sharper edges when you hone away the wear on the back of the blade completely. But it is hard to find much difference in actual work when you sharpen a bit less fastidious.

 

[Trafalgar]

You may have missed an earlier thread where it was pointed out that Brent Beach has a whopping $50 invested in the microscope he uses to draw all of his profuse conclusions. You should read the part of his website where he discusses the blue plastic body of his microscope casting a shade of color on his specimens, and other general lighting difficulties, to decide whether you feel his observations are anywhere near reliable.

After you read about Brent's microscope then please read about a real metallurgical microscope:

http://www.metallurgicalmicroscopes.com/

 

[Corneel]

My microscope was relatively expensive for an USB model, but it is still very difficult to draw any conclusions from the pictures.

 

[Trafalgar]

My microscope was relatively expensive for an USB model, but it is still very difficult to draw any conclusions from the pictures.

True, and professional training in metallurgy, materials science, etc. wouldn't hurt either. I'm sure Brent is a nice guy and his intentions are good but at some point people need to realize he is no expert nor has he equipped himself in any meaningful way, falling way short of even being barely adequate. The images he's captured are not reliable nor, likely, are his interpretations of them. One always allows for the blind squirrel to find a nut every now and then and we applaud him when he does. But, we aren't going to follow him around in our search for them, are we?

 

[woodbrains]

Hello,

Who mentioned Brent Beach, so they can slag him off, from a point of equal ignorance, BTW? Not fair and unnecessarily argumentative. Besides, we do not have to be watchmakers to be able to tell the time.

It is clear that the point at which a wire edge is raised occurs before the wear on the back of the tool is removed. The diagram Corneel provided us shows us this. If this is the point you want to stop, then fine, but it is not the point at which the tool is at its sharpest. Even if the wear bevel on the back is as polished as the hone would produce, it is not at the correct angle, it is dubbed over. I can see this with normal, unaided eyesight, after the wire edge has been raised and removed. The wire edge is an indication that sharpness is approaching, but usually more strokes on the stone are required to get there and remove the wear totally. (Or a ruler trick back bevel) In my opinion, this make the wire edge as an indicator not too useful since we have to recognise by sight when the edge is sharp. (There is no light reflection on a truly sharp edge) If removing the wear is quicker with water stones, then the fact that they may not raise a burr is no disadvantage because I look for sharpness, not feel for it. Besides, our eyes can detect surface deviations 10 times smaller than our fingers can feel. Stropping effectively adds a back bevel, which is as good a way of doing it as any, but why an extra step to an already longer process to preserve the effect of a wire edge, which has no real use, when thought about logically. I used oilstones for decades, and they work fine, but unquestionably take longer to get to similar levels of finish.

Mike.

 

[Trafalgar]

The advantage of using fast media like waterstones and sandpaper is that the process simply gets done and done fast. Why the navel-gazing? This is the chief advantage of these products - one can start at a finer grit and still process a dull edge very rapidly. Call it what you want, we're just removing bluntness. I suppose it would be lovely not to waste an angstrom of steel but obviously a fool's errand in the end. Look, feel, do what you need to do but just remove the steel necessary.

Because of their ability to remove material rapidly, if anything, fast media totally obviate the need for back beveling and all that hoo-hah.

Think about it like this -- if you owned a big kick-a$$ 20"++ wide 3 phase umpteen horsepower planer then a scrub plane wouldn't even rise to the level of quaintness. You don't need it. So goes the back bevel to the extent it's being recommended to remove bluntness. For Pete's sake put the petunias and Shakespeare's sonnets aside and just blow past 'the wear' with the fast media you already own. Oilstone users can just drop back to a medium stone if the edge has really gone off. No big deal, just remove more steel. Let your eye, your thumbnail, sense of timing and experience, hair on your arm, whatever, be your guide.

We're removing what has to be removed. All this other stuff is like becoming fascinated and infatuated with the off-cut from a workpiece instead of the workpiece itself. You removed wood because it was not needed. You're doing the same thing with blunt steel. It's like planing a board to width and all of a sudden becoming perplexed about how to take off the last 64th of an inch and thinking you need to conjure up some new scheme to remove it. Keep on planing. Keep on honing. Until you get where you need to be. I can't possibly imagine anything simpler or more basic.

And yes, if you really push an edge you'll have to remove more steel to make it sharp again and it this might require and additional measure of patience. I'm going to stand by my mailbox awaiting a nomination for the Nobel Prize in physics.

 

[bridger]

My microscope was relatively expensive for an USB model, but it is still very difficult to draw any conclusions from the pictures.

I also have a cheap usb microscope. While I am not declaring that it makes me an expert at anything, and certainly not a metallurgist, it has helped me quite a bit. I'd say it did bump my sharpening up a grade to look at my edges at that magnification.

For instance, this straight razor looks terrible, but shaved pretty well as pictured:

 

[Trafalgar]

Under magnification a lot of edges look like they couldn't cut overcooked pasta.