Behavior of the dull (?) blade (bevel up vs. bevel down?)

[Karl]

Do I remember correctly. Did Adrian say that he was resharpening on a polishing stone only?

This would not remove enough metal to get past the roundness caused by wear.

That's not what I normally do, but I tried it in this case. The puzzling thing is that it seemed to work and the various posts here suggest it shouldn't have.

It clearly isn't working if it's taking you 45 minutes to sharpen one blade!!!

 

[adrian]

It took about a minute instead of the normal 10 minutes. Then the blade resumed cutting and cut for at least another 15 minutes.

 

[Wiley Horne]

However, let's set the comparison of planes aside and focus on the bevel up plane. Here's what may be happening….This analysis is based on your observation that the plane stops cutting prematurely; it stops cutting even though it is sharp enough that it should continue with enough applied force.

A couple preliminaries. The high angle, bevel up set up, in A2, creates a demanding sharpening situation. Compare sharpening the 30 degree primary angle BD blade with the 47 degree BU blade. The overall problem in sharpening the two blades is the same--to remove the lower wear bevel. But here the similarities end. When you work the bevel of a BU plane, you are trying to grind the lower wear bevel off the opposite face--the back of the blade. This is different than working the bevel of a BD plane, where you are removing the lower wear bevel from the same face you are working. Just because of blade geometry, it takes a lot more metal removal from the BU blade than the BD blade--I would say about twice as much--to achieve the same degree of lower wear bevel removal. The large included angle of 47 degrees accentuates this effect, compared to the 30 degree (primary angle) BD blade. Draw a scale picture of this, and you can see how the geometry makes a tougher problem of the high-angle BU blade.

Is most of the wear on the underside? It's not evenly split between the top side and bottom side of the edge?

RESP: The wear is not symmetrical. The upper side wear is longer and flatter than the lower side. No one has discovered the exact shape of the worn edge; Steve Elliott is developing a sophisticated set up for doing just that, and the results should be most interesting! The reason I focused on the lower bevel is because that is most peoples' sharpening strategy, and is developed from the BD blade model. Grind the bevel side until you have reached virgin steel, then smooth the upper bevel somehow (pressure on stone, strop, ruler trick, explicit back bevel). Most folks use the same basic approach on BU blades, but Brent Beach argues for a different approach because of the heavy grinding requirement on the bevel side, which he argues is inefficient. Here is Brent's illustrated thinking on the problem of sharpening and bevels:

http://www3.telus.net/BrentBeach/Sharpen/bevels.html

He advises (among other things) using a 3 degree back bevel on BU irons.

ADRIAN: I drew some pictures and tried to understand the statements you made above. I agree that if the goal is to remove a wear bevel from the underside then things are much worse in the case of the bevel up plane. I do not agree that a large angle (47 deg) is worse than a smaller angle. It would be worse at 33 degrees. In fact, the larger the bevel angle the less metal needs to be removed in this case. (The same result is true for the bevel down case.)

Details aside, it is clear that you have to remove more metal in the bevel up case. This would seem to be a major advantage to the bevel down configuration.

RESP: Adrian, the narrower the included angle of the blade, the more one is 'compressing' the worn edge into a smaller space. Hence, a fixed amount of grinding will remove a greater percentage of wear from the more acute blade. If this were a critical thought, I would include a picture, but it's tangential to the main idea which you state right above--that the BU blade presents special problems in sharpening, compared to the BD blade, owing to the wear on the blade back.

So we're up against 3 things--an abrasive-resistant steel, a large included angle on the blade, and the fact that we are trying to remove a wear bevel on the opposite side of the blade. This latter fact means that you could roll up a burr, and still have wear bevel left untouched. What could be happening is that, even though you are generating a burr on the bevel side of the BU blade, it is not a large enough burr to have fully rolled up the wear bevel on the blade back. Then you flip the blade over and 'back off'--remove the primary burr with the ruler trick--but still there is some wear bevel down there just under the blade edge which is hiding from you. The blade is not quite sharp, still a bit ragged and rounded at the edge.

ADRIAN: What if I actually raise a burr from the back side rather than just cutting off the burr that was produced by working the bevel side? Wouldn't this guarantee that any wear bevel has been removed?

RESP: If you treat the blade back just like the bevel side, and raise a heavy primary burr on both sides, yes, you will have removed the wear from both sides. But is that actually what is happening? Mr. Charlesworth's strategy is to remove the lower bevel wear with an 800g stone, then use the ruler trick as part of the polishing on the 8K-10K stone, to smooth or polish the edge using a small facet (maybe 1/32" width). Is that what we're talking about? If one works the back side of a BU blade sufficient to raise a real burr, then there will be a facet running considerably up the blade back, which would grow with each sharpening--it's hard to foresee all the consequences of this.

ADRIAN: Do you think I should be able to see these things under a 10X loupe? I imagine that if I can detect the wear bevel it will show up as a line of reflection at the edge.

RESP: Yes, a 10X loupe will help immensely. Especially in a lowish, raking light. For practical purposes, something I prefer even better at the bench is a magnifying lamp with a 5X inset magnifier. The reason is that I can take one step and be looking at something up close, with lighting, and under magnification. You can see a lot without heavy magnification, and it fits the rhythm of work.

Anyway, you can test this proposition by grinding back about a millimeter, to where you know you're into virgin metal and beyond any wear bevel. And sharpen that edge. See if you get a longer planing run. If you do, then the original problem was incomplete sharpening due to the factors discussed. If not, then either live with it or try a more acute blade angle.

ADRIAN: I'll admit that I'm reluctant to do this because it'll probably take me a couple hours once I get my camber re-established and everything...and the benefit remains unclear.

RESP: I understand. Here's another diagnostic you could use. Next time you sharpen that BU 47 degree blade, in your regular manner, use a ruler (for the RT) which is twice as thick as right now. In other words, shoot for a 2 degree back bevel. Finish stone only, and keep the width of the bevel very small, because you want to _remove that bevel_ on the next sharpening. If incomplete sharpening has been happening, then the higher back bevel should provide you with a sharper edge and a longer planing run, despite the added loss of clearance. I am suggesting try this as a diagnostic, the remedy (if needed) being more thorough grinding.

ADRIAN: One other observation. Since people keep saying I'm supposed to be able to sharpen in the blink of an eye, I tried a less thorough sharpening approach the last time the blade quit cutting. Normally I've been sharpening at 45 until I get a burr (which means the 47 deg bevel is removed). Remove burr on the back. Then I do 5 strokes in each position (cambered blade) on the polishing stone, and a few strokes on the back again. (All strokes on the back are with the ruler trick.)

But getting the burr at 45 deg takes about 50 strokes (which I then have to do in 5 positions to get all along my cambered edge.) So instead I just did about 10 strokes in each position on the polishing stone and a few strokes on the back. After doing this the plane started cutting again. I didn't closely monitor how long it cut for, but it was at least 15-20 minutes. In other words, it wasn't dramatically shorter than the lifespan I got with a full resharpening. But it doesn't sound like this procedure is adequate to remove a wear bevel on the back.

RESP: Adrian, here is where you're putting your finger on the real problem. As a number of others have said, an efficient method of sharpening is your top priority--then the rest of this bother will go away. My advice, for plane blades and most chisels, is learn to hollow grind. This will change your life for the better in so many ways. Learn to hollow grind right to the edge. Honing becomes trivially easy, and you will embrace sharpening, rather than needing to work around it.

Final thought: I have never planed canary wood, but it looks to me like 20 minutes of planing a Janka 2200 wood at a 59 degree attack is about what is possible.

Does hardness directly relate to edge longevity? This wood is typically described as being easy to work with hand tools despite being hard. (Teak is softer, but worse, from what I understand, due to abrasive extractives.)

No, hardness does not correlate 1:1 with longevity. Abrasive inclusions like silica, as you have said, are a bigger factor. But hardness does matter--note difference between American cherry and canary wood. And it particularly matters when you're attacking at a high angle. As you go from an attack angle of, say, 40 degrees, up to, say, 65 degrees, the mix of penetration versus scraping heavily favors penetration at 40 degrees. But the closer you get to 65 degrees, the more the mix is shifting toward scraping, and especially so as the blade begins to lose a little of its edge off the stone. At 59 degrees, I feel hardness matters quite a bit. You could check this by testing your 59 degree plane on cherry vs. canary wood--does the edge last longer on cherry?

Wiley

 

[adrian]

Hi Adrian

First of all I do think that your expectations of 59 degrees versus 45 degree cutting angles needs to be revisited - there is no way that they will perform the same. The edges do not enter the wood (cut) in the same way, and the abrasive properties of the wood act differently upon them.

I wasn't aware of such a big difference in performance with the previous timber I worked (cherry). So I was surprised. If the answer is simply that high angle cutting requires more frequent sharpening that's a fine answer.

Question - On the BU blade, are you honing a full face or a secondary bevel?

The length of time (45 minutes or 50 strokes) it takes you to hone an edge suggests that you are honing a full face, or a wide secondary bevel, or using too fine a grit. A wide bevel is very inefficient. I take about 2 minutes from start to finish (just a couple of strokes on each stone). I only work a micro secondary bevel. I only use a 25 degree primary bevel. Anything over that will create more metal to remove, especially if you add a camber. Cambering a micro secondary bevel takes very little time.

I'm honing a secondary bevel and then applying a tertiary bevel. The secondary bevel has grown kind of large, I observe. It's about 3mm. I tried to estimate the size of the camber. It looks about 1/3 mm, which is smaller than my intention. I'm not sure if that means the camber has been vanishing in use. (I think my target was 0.8 mm, equivalent to the 1/4 mm recommended by Charlesworth taking into acount the different bed angles.) This kind of limits how small the cambered bevel can be.

Secondly, while the Ruler Trick is generally an excellent strategy for users of honing guides or on BD blades, I avoid it on BU blades. The reason is that I want to strop the back of the BU blade as I work. I do this freehand. The micro back bevel of the RT makes this strategy very difficult, if not impossible. Although the back bevel angle is so small that I doubt it decreases the clearance angle significantly, the back of the blade is now no longer coplanar and I will not be able to reach the back of the blade by running it on the strop. Stropping likely minimises the incusion of a wear bevel, and the edge can be maintained for at least 3 times as long. I might add that I have never experienced the efffects that you described earlier.

I don't understand. Are you applying a back bevel by stropping? (And didn't someone else say stropping was bad in this case?) How does stropping prevent the wear bevel from causing problems?

 

[lwilliams]

My secondary bevels are also very narrow but I've made a device using a laser pointer that allows me to measure the bevels to well less than a half a degree. Here's a picture of a freshly sharpened Hock high carbon blade in the device:

This shows the back bevel (on the left) at about 2.6 degrees and the main bevel at about 29.1 deg.

I've been using this laser thing to calibrate my honing jig, not that it's important to be within .1 degree of anything. I can put a freehand-honed blade in it and get a very accurate result for the angle at the tip.

To keep things in perspective, let me say that I have great respect for your ability to make profiled blades that perform well in your planes. Your specialty is in the mainstream of traditional woodworking and my experiments are more like a high school science project on steroids. But as a hobby it's been a lot of fun and I think my results may be of use to others.

Steve,

I've found your information on cap irons useful and informative but I haven't gone that deeply into your information and don't know much about it. This is mostly because I approach this kind of information with a view tainted by the pseudoscience one finds on sites like Brent Beech's. Brent, Derek and others, IMO, drape their stuff in all the trappings of scientific inquiry but skip the inconvenience of actually following anything close to the scientific method.

An example is Brent Beech's use of information about the cutting action of diamonds used for lapidary polishing: http://www3.telus.net/BrentBeach/Sharpen/grinding.html#crystal. While the information is probably accurate for lapidary work, it has nothing to do with the cutting action of diamonds in steel. When cutting steel the edges formed by the facets actually take tiny shavings as do the tiny cutting edges of the abrasives of a grinding wheel. Go to your grinder and pick up a pinch of swarf and you'll see what I'm talking about. You won't get a pinch of powder, you'll get a clump of a stringy almost fibrous material almost like a little pad of steel wool. Brent also seems to base most everything on two assumptions--first one can't manage the wear on the flat face of the iron and the other is than one can't keep a sharpening medium flat. I think both are wrong.

Right now we're going through a few days of tuning and sharpening tools before a workshop. Don sharpened a favored rabbet plane that had seen a lot of use since its last sharpening. Because we had discussed this thread this morning he noticed a pretty significant wear bevel on the face and what it took to remove it. Removing that wear took only four strokes on a medium India stone. This stuff is really easy if you pay attention to maintaining everything flat and keeping your stones in good shape.

What happens with all this is that people like Adrian get led down a blind alley trying to achieve sharpness with a blunt faceted edge. It's just not a good approach. I don't have time to retrieve him and all the others from that alley, maybe Wiley can help him. I am curious how many failed corpses lie at the end of the alley but I don't care to go looking.

The other thing is this thread caused me to go borrow one of my partners' copy of Leonard Lee's book. I read it a number of years ago but with it in my hands I can say that Lee's information has been misrepresented in nearly every forum thread I've participated in concerning clearance angles. While the claimed content of Lee's book has been often used as an argument as to why what I've said about clearance angles is wrong, I'm finding it's one of the strongest supporting sources around.

Some of what I found there were the macro-photographs in Appendix 1 dealing with classification of chip formation. In these, one can easily see the cutting edge is below the surface of the surface left by the cut. One can see the spring-back of the wood fibers swarming behind the cutting edge like water behind an oar. It appears as if the clearance angle of the tool used is a pretty constant 15º while the cutting angle varies. It's clear from the photos that even a 15º clearance angle isn't enough with steep cutting angles.

 

[bugbear]

Note that I've never stropped and I currently use the ruler trick on the back.

Since Lee Valley blades have always been "fairly flat", and many of them are now lapped flat, why are you using the ruler?

The ruler trick is a fine way of avoiding the labour of bringing a large, rough area to full polish (I'll call this "blade preparation", in contradistinction to "sharpening"). This can be very laborious if the blade is old, pitted, distorted, or simply very roughly ground (or a combination!).

In these circumstances the ruler trick provides a method of performing repeatable, localised polishing. The repeatability is importantly, since you need to work the back during normal sharpening, if only to remove the burr.

Without the consistancy provided by the ruler trick it would be harder to avoid either leaving some burr, or having the back bevel thicken and grow, in the same way that hand bevels tend to.

BugBear

 

[Ikisumu]

What happens with all this is that people like Adrian get led down a blind alley trying to achieve sharpness with a blunt faceted edge. It's just not a good approach. I don't have time to retrieve him and all the others from that alley, maybe Wiley can help him. I am curious how many failed corpses lie at the end of the alley but I don't care to go looking.

Heh, you are very much right in very many ways. Then again, so much of those things you point out are more or less food for thought, if not plain fun for both those who brought them up and for those who read about them. The richness lies within diversity of things as well.

I can see why you pick up Mr. Beach's assumption as an example. His assumption is nothing more than an assumption on his behalf for he has no actual scientific methods within his reach to transform his assumption into a well-founded conclusion. And certainly in this case the assumption would cease to exist. It does not work that way with useful states of different steels, and seemingly in his case he needs to see it by himself.

Ok, there is certainly a kind of a problem if merely something of an assumption will suddenly grow a body for itself, only to start squirming along the freeways of the internet. It will be killed out there in the end, but I admit it can take time, too.



If getting back to the topic, it has already been quite clear for a while now that member Adrian would have use for an actual accomplished live tutor, who would guide him to choose a logical set of sharpening accessories and to apply those in a manner where it consumes the least of time and energy versus sharp enough blade. That kind of crash course would become a nice starting point to keep on developing skills further.

Samu

 

[Derek Cohen (Perth Oz)]

I wrote ...

Stropping likely minimises the incusion of a wear bevel, and the edge can be maintained for at least 3 times as long.

Adrian wrote ...

I don't understand. Are you applying a back bevel by stropping? (And didn't someone else say stropping was bad in this case?) How does stropping prevent the wear bevel from causing problems?

Hi Adrian

I do strop - not to remove a wire edge after sharpening, as I suspect David was suggesting - but instead between sharpenings to maintain the sharp edge. Just remove the blade and run it over a leather strop with green rouge ...

It is not reasonable to strop the microbevel on the bevel face, and so I choose a second best alternative, this being to strop the back of the BU blade. As it happens, however, that is the side where half (or more - if the research is accepted) of the wear occurs with BU blades.

You ask a good question whether this is equivalent to a back bevel of sorts. I do not know - I am in the process of building my electron microscope and so I shall soon be able to say. In the meantime all I can add is that it works. My BU blades stay sharp a long time and are no more effort to re-sharpen.

Larry wrote of Steve's post:

I've found your information on cap irons useful and informative but I haven't gone that deeply into your information and don't know much about it. This is mostly because I approach this kind of information with a view tainted by the pseudoscience one finds on sites like Brent Beech's. Brent, Derek and others, IMO, drape their stuff in all the trappings of scientific inquiry but skip the inconvenience of actually following anything close to the scientific method.

Larry, it is amazing how little actual scientific research you can quote of your own. Any at all? Guys like Steve and Brent make an effort to provide reproducible experiments. Now that is a good definition of scientific methodology is my book. What we get from you is rhetoric, which is hardly scientific in any one's book. Stop your usual strategy - when you are struggling to win a point - by going for the person and not the ball.

Regards from Perth

Derek

 

[Ikisumu]

Hello Mr. Cohen,

You ask a good question whether this is equivalent to a back bevel of sorts. I do not know - I am in the process of building my electron microscope and so I shall soon be able to say.

That certainly sounds like a fun project. If it is based on a commercial frame, there is still a lot of spare parts available for very old models as well.

Or are you making the frame as well with a special size chamber with rotating crossfeed table with holder for large parts? I so, I think the best source and advice would be found from classic JEOL formats for special SEMs for manufacturing quality control. Furthermore, if it was me into this kind of project, I would seriously consider adding up an EDS/WDS analyzer in it as well.

However for to examine just surface topographies, I have a reason to propose that an AFM with a mapping software would be perhaps more definitive method in this sense.


********

As an academic technical research scientist and materials developer in materials sciences (that has really been my dayjob for past 15 years), methods producing repeatable results are in such a simple cases often not that difficult to achieve locally at all. One just needs to be systematic (which is certainly an art in itself).

But then, to transfer those results of one's research into universal use of others without essential/significant loss of process information can be truly painful to work through. Especially when the issues are based on dynamical interaction of materials, like it is in the case of successful sharpening.

The first issue is dynamical interaction of interfaces, which is often already a difficult concept to visualize. Then there are essential materials (steel, stone, fluid), which are always reflecting their performance based on their inherent properties and general quality.

Dynamics, properties, quality. It is a kind of holy trinity, each of them demanding special attention. If attention is paid sufficiently, there will occur developmet of skills. Otherwise there will be only development of experience.

Of course I do know that most people will never have an access to a situation where they could see and try out all of this on their own, instead all what they can do is to only hear about them. In that situation, the best favour what can be done is to explain the thing at hand without any coloration of opinions without foundation. Another challenge in this task is to learn how to connect the necessary terms and idioms with the target audience. The main point after all is to transfer the results. Further development and validation of methods and materials will be then much easier.

Sorry for this off topic.

Samu

 

[Paul Chapman]

This has now become so over-complicated it's almost embarrassing :shock: How hard can it be to hone a blade :? It takes most normal people a couple of minutes..........

Cheers :wink:

Paul

 

[Ikisumu]

This has now become so over-complicated it's almost embarrassing :shock:

It is embarrassing.

In addition, I still can't believe I felt such an urge to write such a rant I did. That is very embarrassing as well.

Samu

 

[Derek Cohen (Perth Oz)]

Derek Cohen (Perth, Oz) wrote:

You ask a good question whether this is equivalent to a back bevel of sorts. I do not know - I am in the process of building my electron microscope and so I shall soon be able to say.

Then Samu wrote:

That certainly sounds like a fun project. If it is based on a commercial frame, there is still a lot of spare parts available for very old models as well.

Or are you making the frame as well with a special size chamber with rotating crossfeed table with holder for large parts? I so, I think the best source and advice would be found from classic JEOL formats for special SEMs for manufacturing quality control. Furthermore, if it was me into this kind of project, I would seriously consider adding up an EDS/WDS analyzer in it as well.

Hi Samu

It was a joke.

However I do have an interest in exploring this area, and I do have a computer-microscope. Not a serious one by your standards - it's a QX3 - but with Steve's help I shall set it up and take a few pics of the dastardly wear bevel in BU planes!

Regards from Perth

Derek

 

[lwilliams]

Larry, it is amazing how little actual scientific research you can quote of your own. Any at all? Guys like Steve and Brent make an effort to provide reproducible experiments. Now that is a good definition of scientific methodology is my book. What we get from you is rhetoric, which is hardly scientific in any one's book. Stop your usual strategy - when you are struggling to win a point - by going for the person and not the ball.

LOL, do you really believe all this stuff is "scientific research?" Can I suggest you Google "scientific method" and refresh your memory as to what it is?

I've never represented what I write to be anything other than my own knowledge or opinion. I've never dressed my stuff up to be anything other than that and hope I don't ever feel the need to enhance my information by using pseudo-science for credibility.

I do try to offer easy ways for people to confirm what I say as I did in this thread here:

../You can verify this by using a more acute 30º bevel angle and you'll see the edge life is greater. If you had an O-1 iron you could go to a 25º bevel and increase edge life even more....

and here:

...I believe you have a couple middle pitch bevel-down planes. Hone one at 37º and give it a try. You'll find you're experiencing exactly what Adrian is reporting. You're plane will quickly start balking not working like you're used to it working...

and here:

... Go to your grinder and pick up a pinch of swarf and you'll see what I'm talking about. You won't get a pinch of powder, you'll get a clump of a stringy almost fibrous material almost like a little pad of steel wool....

When I have an outside source that backs up what I'm saying, I cite the source and quote it. For instance each time I've quoted Machinery's Handbook on the clearance angles for metal working I've gone back and retyped all the information for the quote. In this case, I've done it so many times that the last time I did it I just typed into my word processor and saved the file. It's real easy to quote now, want to see it again? You've never replied and said just why you think wood requires less clearance than metal.

 

[Ikisumu]

Hello Derek

It was a joke.

Haha, I see.

Forgive me not catching a good one, for I indeed happen to know a couple of guys who have actually refurbished old SEM frames for their personal uses. They have equipped those with many kind of extra features, too.

However I do have an interest in exploring this area, and I do have a computer-microscope. Not a serious one by your standards - it's a QX3 - but with Steve's help I shall set it up and take a few pics of the dastardly wear bevel in BU planes!

There is absolutely nothing wrong with QX3. With it, the scratch patterns and the general idea of the topography of the bevel will be presented nicely. All the way down to significant levels, I believe.

However, if possible at all, including a scale in the picture would be the most welcome. For example so many honing stone salesmen tend to present their scratch pattern pictures without a proper scale included, and it just makes the content of the presentation kind of... well, you know.

Samu

 

[Derek Cohen (Perth Oz)]

Thanks Samu, those are good points you raise, and you are a good sport.

Regards from Perth

Derek

 

[adrian]

Note that I've never stropped and I currently use the ruler trick on the back.

Since Lee Valley blades have always been "fairly flat", and many of them are now lapped flat, why are you using the ruler?

...

Without the consistancy provided by the ruler trick it would be harder to avoid either leaving some burr, or having the back bevel thicken and grow, in the same way that hand bevels tend to.

I'm a little puzzled by this. It looks like first I'm asked why I use the ruler and then the answer is supplied. :?:

If you treat the blade back just like the bevel side, and raise a heavy primary burr on both sides, yes, you will have removed the wear from both sides. But is that actually what is happening?

Well, when I sharpen as suggested by Charlesworth, no. However before I adopted his methods I used to attempt to raise a burr from the back on each stone. I'm not sure how successful I was in general at doing so, especially on the polish stone where the blade would stick....and my stones weren't always (ever?) flat back then. In Harrelson's video on sharpening he recommends flattening the back and then only using the polishing stone thereafter. But I got other advice to the contrary, that the back should be worked each time with a coarser stone to remove wear on the back. And to be honest, I always feel a bit uncertain when I work the back without raising a burr: how do I know if I've worked it the right amount?

Note that for the topic at hand, I figured that raising a burr on each side would be a quicker alternative to grinding off the bevel of ensuring that any worn regions are removed.

Adrian, here is where you're putting your finger on the real problem. As a number of others have said, an efficient method of sharpening is your top priority--then the rest of this bother will go away. My advice, for plane blades and most chisels, is learn to hollow grind. This will change your life for the better in so many ways. Learn to hollow grind right to the edge. Honing becomes trivially easy, and you will embrace sharpening, rather than needing to work around it.

Right to the edge? I have seen people recommend staying away from the edge to avoid overheating it. If I want to hollow grind I'll have to buy a grinder....

What happens with all this is that people like Adrian get led down a blind alley trying to achieve sharpness with a blunt faceted edge.

Some of what I found there were the macro-photographs in Appendix 1 dealing with classification of chip formation. In these, one can easily see the cutting edge is below the surface of the surface left by the cut. One can see the spring-back of the wood fibers swarming behind the cutting edge like water behind an oar. It appears as if the clearance angle of the tool used is a pretty constant 15º while the cutting angle varies. It's clear from the photos that even a 15º clearance angle isn't enough with steep cutting angles.

I'm wondering what is meant by "achieve sharpness with a blunt faceted edge"? Does this mean I'm not removing the wear bevels?

Regarding this issue of clearance angles, I'm a bit puzzled by the claim that a clearance angle of 15 deg is required when everybody is using 12 deg planes...and they do seem to cut. Surely this is clearcut experimental evidence that 15 deg is not required.

I do strop - not to remove a wire edge after sharpening, as I suspect David was suggesting - but instead between sharpenings to maintain the sharp edge. Just remove the blade and run it over a leather strop with green rouge ...

How would this procedure be functionally different from doing the ruler trick on the polish stone a stroke or two every so often? Also, if the problem is that I need to remove a wear bevel from the bottom, and everyone says the polish stone can't do the job...why would this? Or to turn it around, is this evidence that the wear bevel isn't as much of a problem as claimed?


So, let me try to focus things a little bit. There are a few different questions circulating in the discussion:

Sharpening:

1. Does my sharpening procedure (however flawed or misguided it might otherwise be) produce a sharp blade or am I producing blades that are somehow defective (not sharp)?

2. What might I change about my sharpening procedure to make it faster, more effective, better, etc., particularly to decrease my reluctance to sharpen sooner rather than later.

Clearance Angle:

3. What is the clearance angle required for effective work? How does it depend on cutting angle? What happens if it is insufficient?

Blade performance and expectations:

4. How long should a blade cut for? How does this depend on the cutting angle?


Now on this list, question 2 is a kind of open ended question that could draw out everyone's personal sharpening scheme. The other questions are of a more theoretical or focused nature. But I'm not sure I detect a consensus in the answers.

Next my observations and experimental evidence. I have observed that the bevel down 45 deg plane cuts even when it is dull. The bevel up plane at 59 deg cut angle stops cutting when still somewhat sharp, and certainly much sharper than the other blade. Three explanations seem to be available: it has to do with shaving thickness, it relates to loss of clearance angle resulting from a wear bevel, or it is due to the higher cutting angle.

Tests I can attempt: try to cut a thin shaving with a dull bevel down plane. (Unfortunately I sharpened it...) Use a 47 deg cut angle blade in the bevel up plane and observe edge longevity---clearance angle is the same.

How big are these wear bevels? I cite some evidence that they must be pretty small. One is that I was able to bring the edge back to life with just a few strokes of the polishing stone. What does this mean? It means that if the wear bevel is responsible for the loss of cut then it must be pretty small, because I must have removed it in 10 strokes on the polish stone. Another observation is that Derek says stropping keeps his edge going for longer. Does this mean stropping removes the wear bevel? (What other explanation could there be?)

If a few strokes of the polishing stone suffice to make the edge cut again, is there a reason to perform a more thorough sharpening?

I inspected my blade with a 10X loupe. I found it very difficult to draw conclusions. I thought that maybe I could see a bevel on the back side of the blade showing up as a fine line of reflection. I didn't feel like I had much certainty in the observation. If I hadn't been looking for it I wouldn't have seen it. This seems to indicate that the wear bevel must be extremely small. How big does it need to be to show up clearly? On the other hand, the edge did not look to be in great shape. The loupe revealed a few small nicks. The back surface polish has scratches from a coarser grit not fully removed.

I've stated that I get 15-20 minutes or so of use out of the blade. Several people have said that this is normal for work in a hard timber with a high cutting angle. In that case, everything is as expected, and maybe there is no need to talk about clearance angles or wear bevels.

I have ground the secondary bevel back to about 1/2 mm and am ready to resharpen.

 

[Derek Cohen (Perth Oz)]

Hi Adrian

If you get 15-20 minutes of planing hardwood, at 59 degrees, then I would say that you are doing just fine.

What I would suggest, as an experiment, is to return to your original method of polishing the back up to your finishing grit, and thereafter not touching it with anything less (ala Harrelson Stanley) but not add a Ruler Trick. See if there is any difference. Then experience stropping the back of the blade - do so before you begin to experience any dullness. Compare the three set ups you have used. Let us know what you find.

Regards from Perth

Derek

 

[woodbloke]

This has now become so over-complicated it's almost embarrassing :shock: How hard can it be to hone a blade :? It takes most normal people a couple of minutes..........

Cheers :wink:

Paul

Paul has salient point. Good grief...sharpen the blade for God's sake and plane some wood! (also meant in jest) - Rob

 

[adrian]

Paul has salient point. Good grief...sharpen the blade for God's sake and plane some wood! (also meant in jest) - Rob

I like to understand what I'm doing. If I observe things I don't understand and I just keep working...then I won't learn and my skills won't improve. That is why I ask these sorts of theoretical questions. Yesterday I didn't have much time in the shop (not unusual) and grinding back the blade consumed it all. Today I hope for better things.

 

[Sgian Dubh]

This has now become so over-complicated it's almost embarrassing. How hard can it be to hone a blade.

With the intent of offering a completely unscientific approach to sharpening, just a hand-me-down technique quite possibly used in thousands of workshops for generations, and for the education of no-one, posting a link to this hoary old chestnut at this point seems apposite. Slainte.