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

[adrian]

Hi Adrian,

My experience is that if a plane 'just stops cutting'--meaning downward pressure won't hold it in the cut--then you're out of clearance angle.

This is very helpful to know. It explains why the bevel up and bevel down planes behave differently.

With the bevel up plane (unless it's a Holtey 98 ), the plane will be bedded at 12 degrees

Little beyond my budget, I fear.

Here's a suggestion: Do you have a grinder? Or a belt sander? If so, get a fresh start on the bevel up blade by removing some metal. Take a square and mark the blade back about 1mm up from the current edge, and grind back to that line. That should get rid of any rounding or excessive wear on the blade back near the edge. Then, going forward, sharpen more frequently so that you are removing the wear and not allowing it to accumulate over sharpenings. And to control what your sharpening may be doing do to the blade back, use David Charlesworth's ruler trick (and no other stropping or microbevels) to limit the clearance loss to 1 degree.

I don't understand how this procedure would change anything. If I hone until a burr is raised and then work the back (with the ruler trick) until a burr is raised then haven't I removed any worn area?

(Note that I've never stropped and I currently use the ruler trick on the back. I've been attempting the sharpening method described by Charlesworth where I sharpen at 45 degrees on the 1000 grit stone and then at 47 degrees on the 8000 grit stone.)

 

[lwilliams]

Of course I raised the bevel angle quite intentionally, as the wood has some grain reversals that tend to give tear out with a 45 degree cutting angle. So I don't want to go to a more acute bevel angle. I'd rather not deal with adding a back bevel to increase the clearance angle if it can be avoided.

Another observation is that the blade doesn't seem to have worn at a faster rate, but to have stopped cutting at a faster rate. Is it possible that the dust that sticks to the bevel is decreasing the clearance and interfering with the cut? (I have noticed that with the canary wood the blade tends to accumulate a layer of dust around the edge that cannot be removed with just a dry cloth.)

A back bevel of any type will reduce your clearance angle. I have no doubt you were using the steeper cutting geometry intentionally. I was only offering a way you could verify the issue is indeed the clearance angle. I think you're missing the wear bevel that appears on the back of the iron quickly in a configuration like you're using.

 

[lwilliams]

According to Leonard Lee's results in his sharpening book, you need a minimum of 5 degrees in hardwood, or else the plane will not work. If you are not sharpening frequently, it's pretty easy to lose the cushion of 7 degrees of clearance to accumulated wear on the lower blade surface, or rounding due to stropping on the back of the blade. Others have reported (sorry, I don't have the links to hand right now) that planing with a high attack angle, like 59 degrees, will accelerate the wear noticeably, compared to the same plane at, say, 50 degrees.

Results? What results? I've read and reread Lee's stuff ( http://tinyurl.com/3abjmbs ) and I don't see any experiments. No research, just a few statements and I can't find where he says what everyone has been reporting.

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. Set up this way, you'll be working with an 18º clearance angle and a 55º cutting angle. If an 18º clearance angle with a 55º cutting angle isn't adequate for a bevel down plane, why would an 11º clearance angle with a 59º cutting angle be perfectly fine in a bevel-up plane? What is different?

 

[Steve Elliott]

Results? What results? . . .
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. Set up this way, you'll be working with an 18º clearance angle and a 55º cutting angle. If an 18º clearance angle with a 55º cutting angle isn't adequate for a bevel down plane, why would an 11º clearance angle with a 59º cutting angle be perfectly fine in a bevel-up plane? What is different?

I've done a large number of carefully controlled experiments using planes bedded at 45 degrees with blades honed to a final bevel angle of 34 degrees. This leaves exactly 11 degrees of clearance when the blade is fresh. In none of my tests did the plane balk. While I usually stopped the tests after about 600 lineal feet of planing it wasn't because the plane was balking, but rather because I'd passed the point where I would expect a competent woodworker would resharpen. I did a few tests that went to 1,000 lineal feet or more and was still able to keep the blade in the cut.

Given that my results with 11 degrees of clearance were so good, I do not believe that a bevel-up plane with 12 degrees of clearance will show inherent clearance problems. My own experience with low angle block planes bears this out.

 

[lwilliams]

...Given that my results with 11 degrees of clearance were so good, I do not believe that a bevel-up plane with 12 degrees of clearance will show inherent clearance problems. My own experience with low angle block planes bears this out.

And the accelerated dulling and wear bevel to the back of the iron so many like Adrian report in these 12º bevel-up planes is the result of? The problems I experience with my own middle pitch planes on those occasions where I got lazy and increased honing angle rather than spend a minute or two regrinding resulted from? In one way or another, I deal with clearance angles almost every day in my work. They're all too real and critical.

on edit: I'm having trouble equating your 600 lineal feet to real world at the bench. I have no idea of how many feet of a single pass I expect to take with a plane. I think more in terms of hours of use and I expect to get at least an hour or two of steady use from a sharpening. I also don't know what you expect in terms of surface quality or how much extra work you're willing to exert.

I can give a good example from history where the structurally flawed wooden miter plane eventually replaced the strike block which cost only 1/3 as much and I can show that inadequate clearance angles were the most likely contributing factor.

It's also really easy to demonstrate burnished surfaces that result from inadequate clearance angles. Burnished surfaces inhibit adhesive, finish and especially stain penetration. Burnished surfaces are a problem in most Western style woodworking applications.

 

[Steve Elliott]

And the accelerated dulling and wear bevel to the back of the iron so many like Adrian report in these 12º bevel-up planes is the result of? The problems I experience with my own middle pitch planes on those occasions where I got lazy and increased honing angle rather than spend a minute or two regrinding resulted from? In one way or another, I deal with clearance angles almost every day in my work. They're all too real and critical.

I've been reading reviews of bevel-up planes since their emergence as smoothers and I've followed a number of hand tool messageboards for ten years without hearing much about "accelerated dulling and wear bevel to the back of the iron so many like Adrian report in these 12º bevel-up planes." During the same time I've been using a microscope to examine the wear that forms on the lower surface of the cutting edge. I don't consider myself an expert on many phases of traditional woodworking, having used power tools for the most part in my professional career, but in the area of blade geometry and wear I think I've done enough careful work that I know what I'm saying and can back it up.

After reading your dismissive comments about jigs I've started to wonder how closely you know what the bevel angle is at the tip of your freehand-honed blades. Your recent description of a strike block plane bedded at 40 degrees that left a burnished surface on the wood with a freshly honed blade "at 30 degrees" made me wonder whether that angle was just a guess. Do you have a way of measuring the angle at the very tip of a blade? Even a little bit of rocking will leave the tip at a higher angle than the overall bevel. I'm not trying to criticize, but rather to understand how the performance you describe could be so different from my own experience.

One correction I'd like to make to my previous post is that the 34 degree bevel was the result of a 31-1/2 degree main bevel and a 2-1/2 degree back bevel. This means that the clearance angle was 13-1/2 degrees rather than the 11 degrees I described. I stand by my good experience with block planes bedded at 12 degrees. These clearance angles are still much less than the 18 degrees you suggest will cause a plane to balk.

 

[lwilliams]

...I've started to wonder how closely you know what the bevel angle is at the tip of your freehand-honed blades. Your recent description of a strike block plane bedded at 40 degrees that left a burnished surface on the wood with a freshly honed blade "at 30 degrees" made me wonder whether that angle was just a guess. Do you have a way of measuring the angle at the very tip of a blade? Even a little bit of rocking will leave the tip at a higher angle than the overall bevel. I'm not trying to criticize, but rather to understand how the performance you describe could be so different from my own experience.

One correction I'd like to make to my previous post is that the 34 degree bevel was the result of a 31-1/2 degree main bevel and a 2-1/2 degree back bevel. This means that the clearance angle was 13-1/2 degrees rather than the 11 degrees I described. I stand by my good experience with block planes bedded at 12 degrees. These clearance angles are still much less than the 18 degrees you suggest will cause a plane to balk.

Actually, I try to keep the honed bevel at the edge small enough that it would be incredibly difficult to measure it. Am I working to within a 1/2º? I seriously doubt it, I freehand hone. Frankly, if I had to use a honing guide I'd be in trouble because there isn't a honing guide made that can handle a large percentage of the profiled irons I sharpen. Let me point out that you don't know yours either. Unless you're also abrading away your honing guide, your angle changes with each pass on the stone. In the case of the acute 2 1/2º back bevel, that change becomes very significant in a hurry.

 

[Steve Elliott]

Actually, I try to keep the honed bevel at the edge small enough that it would be incredibly difficult to measure it. Am I working to within a 1/2º? I seriously doubt it, I freehand hone. Frankly, if I had to use a honing guide I'd be in trouble because there isn't a honing guide made that can handle a large percentage of the profiled irons I sharpen. Let me point out that you don't know yours either. Unless you're also abrading away your honing guide, your angle changes with each pass on the stone. In the case of the acute 2 1/2º back bevel, that change becomes very significant in a hurry.

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.

 

[Wiley Horne]

Hi Adrian,

My experience is that if a plane 'just stops cutting'--meaning downward pressure won't hold it in the cut--then you're out of clearance angle.

This is very helpful to know. It explains why the bevel up and bevel down planes behave differently.

Here's a suggestion: Do you have a grinder? Or a belt sander? If so, get a fresh start on the bevel up blade by removing some metal. Take a square and mark the blade back about 1mm up from the current edge, and grind back to that line. That should get rid of any rounding or excessive wear on the blade back near the edge. Then, going forward, sharpen more frequently so that you are removing the wear and not allowing it to accumulate over sharpenings. And to control what your sharpening may be doing do to the blade back, use David Charlesworth's ruler trick (and no other stropping or microbevels) to limit the clearance loss to 1 degree.

I don't understand how this procedure would change anything. If I hone until a burr is raised and then work the back (with the ruler trick) until a burr is raised then haven't I removed any worn area?

Adrian,

I should have mentioned this before, but we are comparing a plane attacking at 45 degrees with one attacking at 59 degrees--the 59 degree plane is approaching a scraping angle, and will have a shorter blade life. Especially against a wood with 2200 Janka hardness, which is way harder than sugar maple. A better comparison would be to grind the BU blade to 33 degrees or so (as Larry Willliams suggested), so that both planes are attacking at 45 degrees.

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.

Plus, A2 is a wear-resistant steel. It resists metal removal, even though you need to remove more metal from the BU blade.

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. So even after sharpening, it's halfway on the path to dull, and sure enough the lower wear bevel sets up more quickly than it should, and soon the plane can't be held in the cut. [In this situation, reasonable people can debate whether the lower wear bevel has grown to the point where clearance is limiting, or whether you just have a rounded dull edge which can't get a bite.]

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.

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.

Wiley

 

[Paul Chapman]

Great analysis, Wiley - it's all about getting rid of the rounded over portion of the edge which develops as the blade blunts. Quite easy to see with a low-power magnifying glass whether the roundness has been removed.

Cheers :wink:

Paul

 

[bugbear]

In the past I could expect to spend 45 minutes sharpening one plane. This doesn't encourage frequent sharpening. If everything is going well I have been able to do it in something like 5-10 minutes lately, but things don't always go well.

OK, this is odd. Even David Charlesworth, known for his (ahem) "methodical" approaches sharpens a plane blade quicker than that on his video, including all the exposition.

45 minutes is long enough to recondition a fairly knackered "car boot" blade!

BugBear

 

[woodbloke]

In the past I could expect to spend 45 minutes sharpening one plane. This doesn't encourage frequent sharpening. If everything is going well I have been able to do it in something like 5-10 minutes lately, but things don't always go well.

OK, this is odd. Even David Charlesworth, known for his (ahem) "methodical" approaches sharpens a plane blade quicker than that on his video, including all the exposition.

45 minutes is long enough to recondition a fairly knackered "car boot" blade!

BugBear

Agreed...if you're spending 45 mins to hone a blade, something is drastically wrong! - Rob

 

[adrian]

I should have mentioned this before, but we are comparing a plane attacking at 45 degrees with one attacking at 59 degrees--the 59 degree plane is approaching a scraping angle, and will have a shorter blade life. Especially against a wood with 2200 Janka hardness, which is way harder than sugar maple. A better comparison would be to grind the BU blade to 33 degrees or so (as Larry Willliams suggested), so that both planes are attacking at 45 degrees.

I agree that if I want to focus on the bevel up vs. bevel down issue that getting the cutting angle the same makes sense. I think my other BU blade is sharpened at 35 which is closer, at least, so maybe I can try comparing that one.

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?

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.

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.

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?

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.

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.

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.

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.

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.)

 

[adrian]

In the past I could expect to spend 45 minutes sharpening one plane. This doesn't encourage frequent sharpening. If everything is going well I have been able to do it in something like 5-10 minutes lately, but things don't always go well.

OK, this is odd. Even David Charlesworth, known for his (ahem) "methodical" approaches sharpens a plane blade quicker than that on his video, including all the exposition.

45 minutes is long enough to recondition a fairly knackered "car boot" blade!

BugBear

Agreed...if you're spending 45 mins to hone a blade, something is drastically wrong! - Rob

In the past my stones weren't flat and I would work for ever to try to get the burr to reach the edges of the blade because the bevels (and the backs) weren't flat. Fixed that, I think.

I did say that the 45 minutes case occurs when things aren't working properly. One example is the blade slips in the honing guide and I take strokes with it crooked at too high and angle.

Now David seems to get by with a lot fewer strokes than I need. I'm not sure exactly why that is. If it's his stones, or the size of my secondary bevel. I usually seem to require 50-100 strokes at each position along the camber.

I've been sharpening some blades (including this one) by methods based on his video. Before I spent a lot more time on the polishing stone. I'm not sure if stinting on the polishing is OK...though the blades do seem to cut. I just read recently somewhere (maybe in Hock's book?) that a greater understanding of the metallurgy leads one to polish more.

 

[bugbear]

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.)

I don't understand this at all. I simply can't visualise what you're doing.

50 strokes is a LOT. To me it means you're either removing too much metal, or using too fine an abrasive.

How cambered is your edge? (i.e. what's the "sagitta" of the curved edge).

When you say "5 positions", are you trying to approximate a curve by multiple straight lines?

Are you using a honing guide?

Are you re-locating the blade in the guide (if used) for each "position"?

BugBear

 

[adrian]

I started a new topic at https://www.ukworkshop.co.uk/forums/post495251.html#495251 to talk about basic sharpening in the hopes of keeping this one for talk about relief angles and blade geometry. In my new post I answer Bugbear's questions about my sharpening technique.

 

[bugbear]

Great analysis, Wiley - it's all about getting rid of the rounded over portion of the edge which develops as the blade blunts. Quite easy to see with a low-power magnifying glass whether the roundness has been removed.

Cheers :wink:

Paul

Hmm. Actually a good loupe (say 8x or 10x) might be a wise investment for Adrian. And anyone else, for that matter!

BugBear

 

[Derek Cohen (Perth Oz)]

Hi Adrian

I am late to the thread, and there is little I can add to the excellent information you have received from Steve, Wiley and Larry. I am not going to go there, but will instead make a couple of observations and suggestions.

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.

From your description I would argue that you can significantly improve your sharpening of a BU blade.

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.

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.

What I am also trying to be clear on is that the problem is not with the wood you are using, but very likely with the way the blade is prepared.

Regards from Perth

Derek

 

[David C]

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.

I like to get a significant wire edge on an 800 stone before moving to the polishing stone.

I also find with an 8 or 10 thousand grit waterstone that there is no need to strop as the wire edge floats off on the stone or the sponge cloth.

Best wishes,
David Charlesworth

 

[adrian]

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.