Plane iron clearance angle study

[Normand Leblanc]

Putting calculus aside for a moment, I believe there is a need to explain how this study was done. It's all written in my blog but some people don't seem to get it right. Just like most studies it's a long read and people usually jump from graphs to pictures without really reading what's there. The "no vertical force" that Patrick bring back all the time looks to be the main problem.

Description of a test after sharpening until complete:
1) plane 5 normal shavings applying whatever force is required (a normal planing)
2) check if the weight of the plane is enough to get a full shaving pushing by the sole. Yes then repeat 1. No, then test completed.

Step 2 could a be to check the blade with a microscope or something else.

By doing the check for step 2 with the weight of the plane I know that at this moment - when I cannot get a full shaving - the blade has been worn just enough so that a weight (the plane in this case but it could be 20 or 50 pounds or whatever you want) applied to the worn edge surface is not enough to engage a cut.

All the tests have been done with the same method. That means that each and every test is stopped when the same weight (the plane) cannot force the blade to take a shaving.

This study got me to realize that, when we stop planing, it's not really because the edge is dull but because the size of the flat under the blade requires that we put a lot of pressure to engage the blade - the blade skip. That flat is the real problem. If you think that it's not the case then you will have to explain why I got close to double the number of shaving at a sharpening angle of 28° compared to 34° all else being the same.

Also, can someone explain why all the old blades from Stanley, Record and Millers Falls are manufactured at 25° if the proper angle is 30-35°. I've never seen a higher angle written on any blade, did you? At the time, the whole world was using hand planes. I'm quite sure they knew what they were doing.

[Stewie Simpson]

The notion that there lacks any clear evidence to advocate a final honing angle of 28/30* is far from true; one need only refer to early western literature dating back to at least the start of the 19th century to highlight that inaccuracy. When discussing the optimum honing angle its important to identify the type of tool steel being referred too. From a historic perspective we can generally refer to it as being of 01 steel. With the advancement in modern metalurgy; A2 and PM-V11 have now entered the market in competition with the traditional choice of 01 steel. To be clear; I don't have a deep understanding of metallurgy; and as such rely heavily on the advise given by those who really should know; the likes of Ron Hock. The general consensus is that the optimum honing angle for PM-V11 is closely aligned to that of 01 steel; while A2 steel needs a higher honing angle of 2-3* above that determined by 01 and PM. For those that now suggest the optimum honing angle should be increased further to 35* or higher; I have not seen any change of advise from that mentioned previously; that would in anyway validate your line of argument.

It should noted:

Veritas bd plane irons (01;PM -V11;A2 tool steel) are supplied ready to use with a flat primary of 30*; and a 35* micro bevel. http://www.leevalley.com/US/wood/pag...182,48944&ap=1

Lie Nielson bd plane irons (A2 tool steel) are supplied with a flat primary bevel of 25*; with a recommendation to the user to hone a 30 - 35* secondary bevel; to increase the life of the cutting edge when working abrasive, and hardwoods. https://www.lie-nielsen.com/nodes/4065/bench-planes


Why Veritas chose to supply their bd plane irons with a 30* primary angle; let alone subscribing to the same honing angle of 35* on all 3 tool steels; is something I am personally at a loss to understand.

Stewie;

[James Waldron]

That's my point: we don't have the data to be defining much of substance beyond "this works for me" or "I tried that and I couldn't get it to work." There's no substance to any of the conclusions that attempt to define an optimum from the variance of a single variable here as the OP has attempted. Beyond that I have not gone.

And thanks Patrick for correcting my haste.

[Scott DelPorte]

Interesting study Normand.

So would your recommendation to BU bench plane makers be to increase the bed angle to get longer edge retention? I too notice the need to sharpen more often when using a BU smoother, but never attributed it to CA. It would be great if edge retention could be improved by a change like this. I think my plane has a 12 deg angle.

Thank you for doing all the work that this study represents.

[Patrick Chase]

Veritas bd plane irons (01;PM -V11;A2 tool steel) are supplied ready to use with a flat primary of 30*; and a 35* micro bevel. http://www.leevalley.com/US/wood/pag...182,48944&ap=1

Nit-picky, butt...

Yep, they do in fact ship their classic (non-custom) BD planes with 35-deg secondaries. To be honest that may be how I first came to try 10 deg clearance.

The newer custom BD planes ship with a 28-deg primary and no secondary. I think they did that because those planes can be configured with cutting angles as low as 40 deg, so they kept the primary low enough that you can do a 30 deg secondary and still maintain 10 deg clearance.

[Derek Cohen]

Interesting study Normand.

So would your recommendation to BU bench plane makers be to increase the bed angle to get longer edge retention? I too notice the need to sharpen more often when using a BU smoother, but never attributed it to CA. It would be great if edge retention could be improved by a change like this. I think my plane has a 12 deg angle.

Thank you for doing all the work that this study represents.

Scott, I did this a number of years ago, that is, built an infill BU smoother with a 25 degree bed. The reason I did so was partly to explore the clearance/wear bevel issue, and partly to be able to use a hollow ground 35 degree bevel since this was easy to freehand (no need for a high secondary microbevel for a high cutting angle). The plane works extremely well, but I cannot say that it holds an edge better than the equivalent 12 degree bed BU with a 50 degree bevel. I do, however, believe that this is the ultimate set up for a dedicated BU smoother. It certainly is the answer for one that prefers freehanding smoothers with a camber.

The question you raise is another example of a singular solution for graded situation. What you have to keep in mind is that the cutting angle of a BU plane is the bed+bevel angle. So, increase the bed and you can lower the bevel angle (which is what I did). Nevertheless, the bevel angle is still much higher than for a BD plane (which may range between 25 - 35 degrees). For example, if you want a common angle (45 degrees) on a 20 degree bed, the bevel on the BU plane needs to be 25 degrees; on a 25 degree bed, you need a 20 degree bevel. This is moving in the wrong direction for edge retention for smoothers. As soon as you begin planing more demanding wood, the bevel angle needs to increase (since, unlike the BD plane, there is no chipbreaker to use). Back to square one here.

Regards from Perth

Derek

[Stewie Simpson]

Derek; I have never owned a Veritas bench plane; your a proponent of freehand sharpening; do you find the shorter length offered by Veritas a little more difficult to manage compared to the traditional length offered by Stanley and LN.

regards Stewie;

http://www.inthewoodshop.com/ToolRev...tingPlane.html

[Derek Cohen]

Hi Stewie

No real difference. I hold the blade below the slot. What lies above the slot is just extra weight. If anything, the shorter blades may easier to balance for that reason.

The same may be said for the Custom Plane blades. There is an illusion that the blades are shorter. However they are the same length below the slot ...



Regards from Perth

Derek

[Scott DelPorte]

Hi Derek
I appreciate the benefit of all the experimenting you guys have done. And since the cutting angle on a BU is the bedding angle (= CA) plus the bevel grind, I understand how increasing the CA would necessitate reducing the grind angle for a given cutting angle.

One of the things I like about my BU plane is that I can configure it with a 62 deg cutting angle by changing to a blade supplied with 50 deg grind. I sometimes use this on difficult wood with interlocking grain, and can get better results than I can with any of my other planes which cannot go that high. While I share your experience of having no difficulty with sharpening due to the shorter length of the BU irons, I do find it more difficult to sharpen the blades with a higher grind angle because the length of the bevel gets shorter. I am a hollow grind and freehand sharpening guy.

Independent of any potential wear improvement due to a higher CA, a higher bed angle would be a benefit to me because I could use a lower grind angle (with easier sharpening) and still get a high cutting angle. Normand is showing a "sweet spot" in his data that indicates increasing the bedding angle of a BU plane to 17 degrees might improve the wear on irons. And since the increased bed angle would allow me to decrease the grind angle and still maintain a high cutting angle, I would perceive a benefit from that as well. However, Normand's data shows increased wear on the other side of 17 degrees too, although we are forced to extrapolate if we want to draw conclusions about the 25 deg you used in your prototype. If 17 deg is more or less a sweet spot in many of the conditions Normand tested, it seems plausible that the 25 deg bed angle might result in similar wear resistance to the 12 deg angle.

A higher bed angle on these planes might also result in a stiffer structure under the plane iron. Considering the stiffness of the BU blades itself, I am not sure how much it matters, but it cant hurt. Very interesting stuff, and I really appreciate all the work you guys do with experiments like these (making an infill BU smoother with a higher bedding angle), and sharing the results with the group.
Thanks
Scott

[Normand Leblanc]

That's my point: we don't have the data to be defining much of substance beyond "this works for me" or "I tried that and I couldn't get it to work." There's no substance to any of the conclusions that attempt to define an optimum from the variance of a single variable here as the OP has attempted. Beyond that I have not gone.

James,

I believe that the study goes beyond "this work for me". Just look at the various projects that woodworkers are doing with hand tools and the vast majority is being done on soft or medium-hard. Also, most hand planes (maybe 80%?) are bedded at 45°. For sure, very hard wood or end-grain haven't been tested but the study's results are for regular work with regular planes and they are applicable for many project.

Scott,
I freehand all my blades (convex bevel) except for BU when the sharpening angle is more than 40° where I need to use a guide.

So would your recommendation to BU bench plane makers be to increase the bed angle to get longer edge retention?

I wouldn't go that far because, the more I think about it, the more I believe that our BU planes are best for end grain or very very hard wood where the clearance angle is not really a concern. On the other hand, I recently built a large end grain cutting board using mostly 45° bedded planes. At the time, like I said earlier, my freehand sharpening technique got me an angle of anywhere between 30-35°. This board can be seen here http://oldchips.blogspot.ca/2016/04/...ing-board.html

Looking at the resale market for old planes, one has to conclude that low angle type were not popular during a period where everyone was using a plane. It's a bit strange that today many of us are using more BU than BD.

Have a good day,
Normand

[John Schtrumpf]

... It's a bit strange that today many of us are using more BU than BD.

Have a good day,
Normand

BU planes are the gateway drug to the hand tool world

[Kees Heiden]

Having been off-grid for a few days, it seems like I missed a lot of fun!

First, congratulations with your research project. I know there goes a terrible amount of time, energy and money in a project like this (maybe not the last one as you seem to have found a cheap way of doing this). I think we can accept your results on face value. You didn't write how many repeats you did on various bits of wood. I think it might make a difference even within the same type of wood, depending on grain angle, hardness, silica content etc. Just the fact that you saw quite a bit of variation between the different species of wood, makes me think variation is the nature of the beast. But I do see a trend: more clearance is valuable, up to a point.

On a quick browsing of this thread I found some arguing about your conclusion, and I think they are right in saying your conclusion was too conclusive! In your data set a clearance angle of 17 degrees was obviously the one with the least amount of edge wear. But when I only look for the O1 steel data, I see almost a straight line between 20 and 14 degrees of clearance. Personally I am not interested in the newer steels. O1 and W1 come with the antique tools I love so much, so in my case I would see the optimum clearance angle would be anything above 14 degrees, and because I also love to work with knotty wood, I would like to avoid too shallow of a sharpening angle. So, I guess, my practice of striving for a 30 degree angle, is not such a bad one. But that is a conclusion valid only for my circumstances.

There is one big caveat, like mentioned by Patrick. Your test is only valid for pure abrassive wear. Other edge damage like chipping or folding is important too. I don't read anywhere in your report to see if you checked if these happened at all. According to David Weaver, the blades he likes best are wearing in a purely abrassive way only and he finds that treat in properly heat treated, old fashioned cast steel (close to W1 steel). Even when the edge is getting past its prime, he can still use it with a bit more down pressure, while a chipping blade immediately leaves evidence in the wood surface. To catch evidence of this kind of thing happening in an early phase, I think it is good to have a look with a microscope.

Chipping and folding in O1 and W1 type of steels can be managed through the sharpening angle or through the tempering of the blade. Rasing the sharpening angle helps to strengten the edge, but of course lowers the clearance angle. Looking at your data that might not be of much importance until you start to really go over 30 degrees. If the edge is prone to chipping, it helps to reduce the hardness a little. Some of the old plane blades, especially French ones, can be pretty soft. As long as you don't work very hard kinds of wood you might avoid the opposite of chipping: folding of the edge.

Regarding the idea that endgrain doesn't need clearance, I think this is a misconception. In my idea the wood fibers are indeed not very compressible in the end grain orientation, but they do bend over easilly, especially in softer kinds of wood. You see this very easilly when trying to cut endgrain with a dull edge. You see voids in the surface, where the fibers have bend over too much and have been seperated. When planing end grain with a fresh edge, the fibers are bend over and then spring back, because of the elasticity of the wood fibers. I think this effect is even stronger then the kind of spring back you see in long grain plaining.

[Normand Leblanc]

Hi Kees,
Ya! You missed all the fun.

Those tests took me way longer than expected but they did not cost very much. I'm left with a bunch of new blades... Every result is the average of two test.

Ok, ok. I agree that the wording used, especially in post #1 were too conclusive.

You're not the only one that seems to like O-1 and it gave me the idea to split the results between the soft and hard blades. Here are the results,

Comparing soft and hard steel.jpg

It seems that softer steels don't require a very accurate sharpening angle when compared to harder steels. There is hardly a difference between 20, 17 and 14° for those.

There is one big caveat, like mentioned by Patrick. Your test is only valid for pure abrassive wear. Other edge damage like chipping or folding is important too. I don't read anywhere in your report to see if you checked if these happened at all

I wasn't looking for surface finish at all but except for one test where there was a small knot, I haven't seen anything to get me to believe that the blade was chipped or folded. It has to be remembered that I wasn't wearing down the blade. The blades, after that each test was completed, were still in a pretty good shapes.

Have a good day,
Normand

[Kees Heiden]

The difference between the classic steels and the modern ones is remarkable. No idea why! They sure seem to wear in a different way.

[Pat Barry]

Hi Normand,
The K&K images below are good references. It would be really interesting to see how your various blades show wear by comparison. You probably don't have access to a SEM but maybe you have high enough magnification to see what an O1 and PMV11 blade look like at the end of test. I wonder if they show much back side wear like for example, figures b, d, and e