Plane iron clearance angle.

[Steve Elliott]

I’ve done some investigation of how plane blades wear, including looking at scores of edges under a small microscope. The “bullet point” list of what I’ve found goes like this:

• More wear occurs on the lower side of the cutting edge, making loss of clearance a major factor in the deterioration of planing performance as the blade wears. I’m not sure I’d quantify the amount as three times as much, but it’s significantly more than the amount on the top. Since the shaving slides across the top of the blade and shines it up some it can look like the wear surface is longer on top, but the shined-up surface is not worn away significantly.
• The minimum honing angle for a plane blade needs to be somewhat larger than for a paring chisel because the plane blade is raised at a higher angle as it meets the wood, which increases the chance of chipping or folding of the edge. For most types of steel a final honing angle of about 30 degrees is good. For A2 an angle of 32 or 33 degrees is better. For planes with a low bed angle a somewhat more acute honing angle can be used.
• As long as the angle is not too acute (which causes chipping or folding) a more acute angle provides longer edge life than less acute one.

Here’s a link to a page on my website that shows the shape of a worn edge:
http://bladetest.infillplane.com/html/w ... files.html
A similar image can be found in Bruce Hoadley’s book “Understanding Wood.” I’ve also seen an electron microscope image showing the shape of a worn planer blade that clearly shows more wear on the lower surface.

 

[bugbear]

• More wear occurs on the lower side of the cutting edge, making loss of clearance a major factor in the deterioration of planing performance as the blade wears.

I'm trying to think through the implications of that for bevel down/bevel up planes, specifically (re)sharpening.

It's making my head hurt.

BugBear

 

[matthewwh]

Hi Steve,

Thanks very much for your input to the thread and the considerable research you have undertaken.

I understand what you have done and why, but not the process that brought you to the conclusion that a more acute angle is less prone to wear.

I am reliant on humble logic and rational thought here, but it would seem sensible that there is a minimum sustainable thickness of steel for a given number of feet planed. If the honing angle is more obtuse then the minimum sustainable thickness will be reached sooner and the blade will wear more slowly.

Put another way if the lower wear bevel presents a bigger surface area to the abrading surface sooner, it will be abraded more slowly.

If you consider a slender wooden wedge and fat one presented pointy end first to a running belt sander, the fat one will last longer than the thin one. Not a perfect comparison but I hope you get my drift.

 

[Steve Elliott]

Bugbear—
On a traditional bevel-down plane, the larger wear surface is formed on the bevel where it can be ground down quite easily. On a bevel-up plane, the larger wear surface is on the flat side (the back) of the blade, and to remove it completely more of the blade has to be ground off.

Matthew—
I came to the conclusion that a more acute angle gives longer edge life by honing edges at different angles and comparing how long they stayed sharp, measured in lineal feet planed. The details of that test can be seen at http://bladetest.infillplane.com/html/bevel_angles.html
As to the mental picture I have of what is happening, I see the more acute bevel staying thin longer as its arris is worn away. The more acute edge would recede faster as metal is worn off compared to the less acute edge, but the less acute edge becomes fat more quickly as metal abrades. For me an actual test trumps whatever theory I happen to hold. I’m always trying to adjust my thinking to match the test results.

 

[Derek Cohen (Perth Oz)]

Steve Elliott wrote:

• More wear occurs on the lower side of the cutting edge, making loss of clearance a major factor in the deterioration of planing performance as the blade wears.

BB wrote:

I'm trying to think through the implications of that for bevel down/bevel up planes, specifically (re)sharpening.

It's making my head hurt.

Steve wrote again:

On a traditional bevel-down plane, the larger wear surface is formed on the bevel where it can be ground down quite easily. On a bevel-up plane, the larger wear surface is on the flat side (the back) of the blade, and to remove it completely more of the blade has to be ground off.

For me an actual test trumps whatever theory I happen to hold. I’m always trying to adjust my thinking to match the test results.

I have put BU planes to stern tests over the years. I probably use BD planes just as much, but the ability of a BU plane to be used at high cutting angles gives them the edge when smoothing interlinked and abrasive woods (such as Jarrah).

Part of my maintenance regime is to strop blades. Since the bevel face of the BU blade uses a secondary microbevel (to achieve the high cutting angle), stropping is not advisable here (impossible to maintain the bevel angle). Consequently I only strop the back of the blade. While this might appear to be doing half a job, in practice the edge is restored significantly. I can do this about three times before needing to rehone the bevel.

The act of stropping the back of the BU blade removes any “wear bevel”. It simply is not allowed to grow to the point where it might intrude.

Regards from Perth

Derek

 

[David C]

Derek,

I am wondering in what way the ability of a BU plane to be used at high cutting angles differs from the ability of a BD plane to be used at the same angles with a small back bevel?

I have used this method for years and find it more convenient to hone a back bevel at 25 degrees than a bevel at 58 degrees, (if an EP of 70 degrees is wanted). This may seem like a steep EP but it works very well on some rippled Tasmanian Blackwood which Colen Clenton kindly sent me.

best wishes,
David Charlesworth

 

[woodbloke]

It's making my head hurt.

BugBear

You ain't the only one BB - Rob

 

[monoman]

I’ve done some investigation of how plane blades wear, including looking at scores of edges under a small microscope.

Hello Steve,

I have followed your research for some time now. I personally thank you for you efforts thus far and wish you well for the future.

• More wear occurs on the lower side of the cutting edge, making loss of clearance a major factor in the deterioration of planing performance as the blade wears. I’m not sure I’d quantify the amount as three times as much, but it’s significantly more than the amount on the top.

Actually, what I state is the exact opposite.

The face of the blade that is pushing up the shaving (known as the upper wear bevel) wears approximately 3 times faster than the other face of the blade (the lower wear bevel). But they both wear.

The basis for this statement was, in part, Brent Beach's findings, see http://www3.telus.net/BrentBeach/Sharpen/bevels.html

The wear bevel on the lower face was 0.00061" (8 pixels) wide, on the upper wear bevel almost 0.003" (40 pixels). So, we know where the wear bevels begin and end.

I'll continue this later as I'm in the middle of a power outage and am running on off my UPS. Better shutdown before I run out of battery power

Cheers
George

 

[monoman]

Part of my maintenance regime is to strop blades. Since the bevel face of the BU blade uses a secondary microbevel (to achieve the high cutting angle), stropping is not advisable here (impossible to maintain the bevel angle). Consequently I only strop the back of the blade. While this might appear to be doing half a job, in practice the edge is restored significantly. I can do this about three times before needing to rehone the bevel.

The act of stropping the back of the BU blade removes any “wear bevel”. It simply is not allowed to grow to the point where it might intrude.

Derek,
Would you please describe how you strop the back of your BU blade. Do you hold it flat on the strop, or are you stopping a micro back bevel?

Cheers

 

[Derek Cohen (Perth Oz)]

David asked

I am wondering in what way the ability of a BU plane to be used at high cutting angles differs from the ability of a BD plane to be used at the same angles with a small back bevel?

Hi David

I have a number of high angle BD planes that I use (along with high cutting angle BU planes). I can happily get along with both types. With regard the BD planes, I have a variety of types, and my preference is for woodies such as HNT Gordon. These differ from the Stanley type of BD plane in having a lower centre of gravity.

If you continue along a continiuum of high-to-low centre of gravity, then at the high end one have Stanley-type planes and 18 Century woodies (with high frogs/beds and greater height), and at the other end of the spectrum there are BU planes (with low beds).

My experience indicates that a high cutting angle on a low centre of gravity plane (such as the BU types) is easier to push than the same cutting angle on a high centre of gravity BD plane.

There is no difference in the quality of the planed board when used by the different planes. There is only a difference in "feel". Further, the issue of feel is a personal one - no right or wrong here.

The third issue is in the preparation of edges. One of the reasons I use low centre of gravity BD planes is that they are a good compromise between feel/feedback and ease of sharpening. BU planes offer the best feel/feedback but are almost in the same category as the high centre of gravity/high angle planes. The latter are more extreme however ...

The qualifier here is how you sharpen. I must emphasise this point. It will not be the same for all. The following is how I experience it (and others in my category will feel the same). Buit there are others for whom the following will not have any meaning.

My preference is to free hand sharpen blades. I hollow grind all BD plane blades and chisels (even my Japanese ones - following your guidance!). I only use a honing guide on BU plane blades since a secondary bevel is needed to create the necessary cutting angle.

Associated with this is my preference to strop blades as a means of maintaining the edge as long as possible between honings. This can be hugely helpful in this regard. The problem, however, with secondary bevels - especially micro secondary bevels - is that they are impossible to strop freehand.

The BD/low C of G planes with a high bed angle require only a hollow grind to facilitate freehand sharpening. If the bevel angle is done reasonably accurately, such that the bevel face is coplanar, then one can hone and strop directly on the face (along with the microbevel created by the hollow grind). This is the easiest scenario.

The next easiest is a single micro secondary bevel on a BU plane - only one microbevel needed. I can still strop the blade back. This works. Not as good as BD/low C of G, but far better than a double microbevel of the BD/High C of G set up. In the latter case I cannot strop.

In the case of BD/High C of G planes, adding just a single back bevel takes us into the same category as the BU planes. However, the latter are easier to manage (re "feel/feedback").

Once again I emphasise that none of the above applies to those for whom the use of a honing guide is the preferred means of sharpening. This is also not about which method is best. I think that we all know that there is no such thing. There are just too many ways to do the same thing.

Here is a link to my thoughts on my sharpening strategy: http://www.inthewoodshop.com/WoodworkTechniques/BeyondSharpASharpeningStrategy.html

Regards from Perth

Derek

 

[Derek Cohen (Perth Oz)]

Monoman asked

Would you please describe how you strop the back of your BU blade. Do you hold it flat on the strop, or are you stopping a micro back bevel?

George

I strop on a hard Horse Butt leather that is glued to flat hardwood.

I use a mix of green rouge (from Veritas) which is softened with baby oil (scented mineral oil). This allows the rouge to permetate the leather and avoids any clumping.

The blade is angled at 45 degrees, held flat, and pulled towards oneself (i.e. sharp end trailing). Do not push the blade bevel first - it will slice up the leather.

My BU blades typically have a 25 degree primary bevel and a high secondary/micro bevel (e.g. 50 degrees, to create a 62 degree included angle). The microbevel makes it difficult, if not impossible, to freehand strop accurately (that is, maintaining the secondary bevel angle). The back of the blade is left flat (no microbevel). Consequently I only strop this side of the blade. This works well enough to give the blade a second lease on life.

The above is taken from an article on my website: http://www.inthewoodshop.com/WoodworkTechniques/Stroppingwithgreenrougeversesdiamondpaste.html

Regards from Perth

Derek

 

[monoman]

Consequently I only strop the back of the blade. While this might appear to be doing half a job, in practice the edge is restored significantly. I can do this about three times before needing to rehone the bevel.

The act of stropping the back of the BU blade removes any “wear bevel”. It simply is not allowed to grow to the point where it might intrude.

The following images from Brent Beach's site, http://www3.telus.net/BrentBeach/Sharpen/bevels.html, and from Steve Elliot's site, see http://bladetest.infillplane.com/html/w ... files.html are a good representation of what a blade looks like as it wears, (although they seem to disagree as to which face wears the most).

How is it possible that stropping the back of the blade in between sharpenings can prevent the lower wear bevel from intruding? I'm not convinced stropping is having any effect at all as far as the shape of the edge is concerned. But the answer may lie apart from the shape. I've attached part of McKenzie and Karpovich's research findings below. Polishing the cutting edge seemed to have the closest correlation to edge retention.

Wear and Blunting of the Tool Corner in Cutting a Wood-Based
Material
By W. M. McKenzie and H. Karpovich
Commonwealth Scientific and Industrial Research Organization, Division of Btiilding Research, Melbourne, Victoria, Australia

Summary. A study was made of relationships between wear (loss of metal) and blunting (reduced performance) of the corner of a steel cutting tool turning a work-piece of hard fibre-board. Rake angle, clearance angle and surface preparation (grinding, polishing) were varied
and measurements made were the three cutting force components and various wear parameters. It was confirmed that retraction of the edge from its initial position is not a satisfactory index of blunting and that the shape parameter corresponding to compression of the cut surface
(negative clearance) was most influential. Also, for the particular tool and work-piece materials used and in the practical range of bluntness, the ratio of negative clearance to the width of the back wear land, as measured parallel to the cutting plane, was roughly constant. It is evident
that development of a hard, very thin layer on the back face would minimize negative clearance and extend sharpening life. In the practical range for cutting wood and wood-based materials, clearance angle had a relatively small effect on the rate at which negative clearance and cutting
forces increased, and rake angle had negligible effects. It is concluded that these angles should not be increased without taking into account factors other than blunting. Polishing considerably decreased blunting rate, especially of the tool corner, which is especially important in sawing. The expense of polishing may be justified in some exacting operations.

In a recent Rob Cosman video I saw, see http://www.youtube.com/watch?v=Rvop_JCf ... annel_page . Rob uses ceramic stones (Shaptons?) 1,000, 16,000, and 30,000. He uses only the 1000 and 30,000 stones on the bevel, and the 16,000 and 30,000 to back bevel the blade using the ruler trick, (you must be sick of hearing that phrase by now, David). At first I thought, 30,000! What a tosser. Now, maybe not. Maybe the higher polished surface will last longer.

I don't own any 30,000 grit stones so I can't report how well they work. But recently I started stropping all my cutting edges on MDF with Tormek paste (because it's handy, or at hand). Visually, the surfaces are much, much shinier than the finnish straight off the 10,000 stone, and it seems like I'm getting double from a blade before re-honing.

BTW. I don't know how many, or few, micros the Tormek paste is, and I'm using it neat - no baby oil, nada. And MDF seems like a really good surface as it actually quite flat and yet holds the honing paste well.

 

[Derek Cohen (Perth Oz)]

Hi George

I am aware of Brent's research. This is the reason I will say that there is a wear bevel to consider. Otherwise I might poo-poo it. The fact is that I do not experience the effects of a wear bevel as I should if I read Brent's work correctly. So I am trying to explain why there is a discrepancy. I am not the only one to experience the results I get. There many who have replicated my method and have the same experiences. So why the difference?

I can only think that Brent's images reveal a blunted edge, that is, an edge that is worn .. past the point of return. No amount of stropping will bring that one back to life. I just do not let it get that far. As soon as I sense a difference in cutting, I pull the blade and strop it. This is easy to do with a BU blade.

I am not sure if I can offer the images of the chisels (from the article on stropping) as evidence. In its favour the chisels are used BU. They are dovetail chisels and the back of the back of the blade is registered and wearing. Some of these Blue Spruce chisels have not been honed on the bevel face for over 12 months, yet are used at least a few times each week on abrasive hardwood. They have only been stropped.... but then they have been stropped on both the face and the back ...

For what its worth ..

Before stropping ...

After stropping ...

With regard the difference between the Tormek paste and Veritas green rouge, I'd say that they are roughly comparable, but I give the green rouge a slight edge. I do find that the Tormek paste can become powdery, and so I prefer the green rouge on my Tormek's motorised strop (which I do not use very often).

Some prefer MDF over leather. The Horse Butt leather is very hard - almost as hard as MDF, but with a (very) little give. I just like the feel.

For waterstones I generally use 1000/5000/12000 Shaptons.

There is a strong argument in using the higher grits. I prefer to think of an edge getting smoother rather than sharper, and it is accepted by many that a smoother (less serrated) edge will last longer. So I am also interested in the high grit stones (just can't justify the cost one at this time).

Regards from Perth

Derek

 

[bugbear]

I’ve done some investigation of how plane blades wear, including looking at scores of edges under a small microscope.

Hello Steve,

I have followed your research for some time now. I personally thank you for you efforts thus far and wish you well for the future.

• More wear occurs on the lower side of the cutting edge, making loss of clearance a major factor in the deterioration of planing performance as the blade wears. I’m not sure I’d quantify the amount as three times as much, but it’s significantly more than the amount on the top.

Actually, what I state is the exact opposite.

The face of the blade that is pushing up the shaving (known as the upper wear bevel) wears approximately 3 times faster than the other face of the blade (the lower wear bevel). But they both wear.

The basis for this statement was, in part, Brent Beach's findings, see http://www3.telus.net/BrentBeach/Sharpen/bevels.html

The wear bevel on the lower face was 0.00061" (8 pixels) wide, on the upper wear bevel almost 0.003" (40 pixels). So, we know where the wear bevels begin and end.

I'll continue this later as I'm in the middle of a power outage and am running on off my UPS. Better shutdown before I run out of battery power

Cheers
George

Surely the figures you quote from Brent concern the length of the bevel not (neccessarily) the rate of abrasion of that bevel?

BugBear

 

[bugbear]

...and it is accepted by many that a smoother (less serrated) edge will last longer. So I am also interested in the high grit stones (just can't justify the cost one at this time).

IIRC Jeff Gorman used to have a citation/quote from research on this.

It said (again, from memory) that polished (AKA super-sharp) edges are less prone to wear caused by propagation of micro-cracks.

Contrary to the ("common sense"?) notion of a super sharp, polished edge being delicate, it was actually more resistant to damage.

BugBear

 

[Steve Elliott]

One of the few differences of opinion I have with Brent is the shape of a worn edge. Since I consider my own evidence to be pretty thin I usually just let this matter drop. My guess is that the greater wear Brent finds on the upper surface corresponds to the shined-up area I see where the shaving has polished the upper surface without wearing it away significantly. I hope to investigate this more closely at some point.

George, thank you for quoting the research by McKenzie and Karpovich--I’d like to read more of the study. The effect of polishing an edge really interests me. I’ve assembled some strops and honing compound so I can test whether stropping increases edge life.

Recently a message on another hand tool forum contained a link to a study by George Beilby that suggests that stropping works by displacing metal instead of removing it. Here’s the link:
http://books.google.com/books?id=JGVDAA ... q=&f=false

In case that link doesn’t work, you can search Google Books for “Aggregation and Flow of Solids” by Beilby. Sections V and VI are most pertinent to polishing metal. I’m hoping that stropping will be an effective way to take the finely-abraded edges I get using fine diamond compound and smooth them out to give an even better edge.

Bugbear, I’ve noticed in my planing tests that microchipping tends to happen where a somewhat deeper scratch reaches the cutting edge. This suggests that the smoother the surface, the less the chance of chipping. I'm hoping that stropping will provide even more benefit than just reducing chipping.

 

[bugbear]

Recently a message on another hand tool forum contained a link to a study by George Beilby that suggests that stropping works by displacing metal instead of removing it. Here’s the link:
http://books.google.com/books?id=JGVDAA ... q=&f=false

I imagine that "stropping" covers a multitude of sins - I don't think it's a very well defined term, so care will be needed in any discussion.

If the "displacing metal" claim is right, that would put stropping nearing to "steeling" (as in butcher) than honing, which is interesting. IIRC Lee had some spectacular pictures of the effects of a butcher's steel.

BugBear (off to do some reading).

 

[monoman]

The basis for this statement was, in part, Brent Beach's findings, see http://www3.telus.net/BrentBeach/Sharpen/bevels.html

The wear bevel on the lower face was 0.00061" (8 pixels) wide, on the upper wear bevel almost 0.003" (40 pixels). So, we know where the wear bevels begin and end.

Surely the figures you quote from Brent concern the length of the bevel not (neccessarily) the rate of abrasion of that bevel?

No. Not rate of abrasion. Just how much is abraded from each face.

Some here seem to think that the blade starts sharp and after a while looks like the Brent of Steve's drawings when it is dull. That simply is not the case. The blade looks like that from the very first pass - only the scale changes.

 

[monoman]

Recently a message on another hand tool forum contained a link to a study by George Beilby that suggests that stropping works by displacing metal instead of removing it.

Steve,

This is true. But surely the edge being "restored" must be in contact with the strop.

Cheers

 

[bugbear]

The basis for this statement was, in part, Brent Beach's findings, see http://www3.telus.net/BrentBeach/Sharpen/bevels.html

The wear bevel on the lower face was 0.00061" (8 pixels) wide, on the upper wear bevel almost 0.003" (40 pixels). So, we know where the wear bevels begin and end.

Surely the figures you quote from Brent concern the length of the bevel not (neccessarily) the rate of abrasion of that bevel?

No. Not rate of abrasion. Just how much is abraded from each face.

Some here seem to think that the blade starts sharp and after a while looks like the Brent of Steve's drawings when it is dull. That simply is not the case. The blade looks like that from the very first pass - only the scale changes.

Surely the "scale" of the round-end-of-the-blade is damn near a synonym for sharpness?

BugBear