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Thread: Plane iron clearance angle study

  1. #1
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    Plane iron clearance angle study

    Hello,
    About a month ago we had a discussion on clearance angle and I said that a study was coming. So here it is.

    The following graph would be a nice resumé

    All test combined.jpg
    This graph is saying that a 17° clearance angle (CA) is the best and that the number of shavings is reduced linearly if the CA is reduced.
    The full study can be found http://oldchips.blogspot.ca/2016/06/...nce-angle.html

    I am quite sure that some people will want to argue the results because they are not sharpening at the right angle for years, just like me. Now that I know what's the proper angle, I'm going to have to adapt my sharpening method. I don't have to but it's not difficult to adjust my free hand technique.

  2. #2
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    Interesting study - and a lot of work. But thanks, I think this will be very useful.

    Interested to read what those with more hand tool experience than me think.

  3. #3
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    Pardon my ignorance, but does the phrase "clearance angle" refer to? Thanks.
    -Howard

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    Interested to read what those with more hand tool experience than me think.
    I think it is great someone took the time to do such a test.

    Quote Originally Posted by Howard Pollack View Post
    Pardon my ignorance, but does the phrase "clearance angle" refer to? Thanks.
    -Howard
    It is the angle formed between the side of the blade contacting the work at its point of contact to the work piece. As an example with a Stanley bevel down bench plane the blade is bedded at 45º. A bevel at 25º would leave a clearance of 20º.

    jtk
    Last edited by Jim Koepke; 06-23-2016 at 1:10 AM. Reason: wording
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  5. #5
    Normand, I think it's a great study, and I salute you for doing it. Just one comment.

    You have two variables: the sharpening angle and the clearance angle. The latter is dependent on the former. You assume that what matters most is the clearance angle, but I think that's an untested assumption, unless I've missed something in your data.

    Let me give you two examples. In your tests, you find that a sharpening angle of 28° (which results in 17° clearance) is best. Suppose we change the bed angle to 50°. Do you think that a sharpening angle of 33°, which would still result in a 17° clearance angle, would be best? I don't know, but I suspect it would not. I suspect that a sharpening angle of around 28° would still be best, so your optimum clearance angle would be around 22°. In your test, a clearance angle of 20° is worse than 17°, but I strongly suspect that's because at CA = 20°, the fragility of the bevel (which is sharpened at 25°) overwhelms the increased clearance.

    Second example: suppose we lower the bed to 38°, the lowest angle that's commonly used in BD planes. Would a clearance angle of 17°, resulting in a sharpening angle of 21°, still be optimum? I'm pretty sure it wouldn't, that the iron would fold almost immediately at 21°. I suspect that the optimum clearance angle would be higher, maybe around 10°, which would give a sharpening angle of (again) around 28°.

    In other words, I suspect (but cannot prove!) that a sharpening angle of around 28° is going be optimum for a wide band of bed angles centered around 45°, and so the optimum clearance angle will vary with bed angle.

    Don't get me wrong, I thing your study is really useful and important. After all, 45° is by far the most common bed angle for BD planes, so your results have important practical implications for the majority of BD users. The bottom line, that a sharpening angle of around 28° results in the most durable edge for a 45° bed in most situations, is clear. But whether that's due to the sharpening angle or the clearance angle, I think the jury's still out on that one.

    Thanks again for doing this!
    "For me, chairs and chairmaking are a means to an end. My real goal is to spend my days in a quiet, dustless shop doing hand work on an object that is beautiful, useful and fun to make." --Peter Galbert

  6. #6
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    I would like to understand your sharpening process and the resulting geometry a bit better if you don't mind. You described your sharpening process as :
    "Sharpening:
    - Grind the blade at a 22° angle.
    - Primary bevel on rough stone at 23°.
    - First micro-bevel at 24° on a fine India stone.
    - Second micro-bevel à 25° on translucent Arkansas.
    - Repeat the process for 28, 31, 34 and 37° (clearance angle of 20, 17, 14, 11 and 8).
    - All sharpening were done with a back-bevel of 1°"

    I'm having trouble understanding the resulting shape of all these micro-bevels.

    Could you describe how wide these various micro-bevels are? If you don't mind providing a quick sketch of what you think the resulting combination bevel looks like it would be great. Is the final micro-bevel (25°) the one that you use to determine the clearance angle (therefore 20° in this example)?

  7. #7
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    If someone is to have a CA of 17°, as this study suggest, then a primary bevel of 25° would be recommended. This 25° with one or two micro-bevel will achieve around 28° at the cutting edge leaving a CA of 17°. It is believed that LeeValley should have their blade ground at 25° instead of 30°.
    Hi Normand

    I, too, applaud the creative thought that went into your study. Woodworking knowledge benefits from efforts such as yours. However, I echo Steve's comments, and would have made the same points.

    The problem with specifying an optimum bevel angle for a plane, as noted in the quote from your web page, is that it ignores the properties of the steels involved. For example, most steels do not have the longevity at 25 degrees that they would have at 30 degrees. This is a factor known for many years, and one I have demonstrated in my own research. It applies to O1, A2 and PM-V11 steels alike. Indeed, David Charlesworth will argue that 35 degrees is the optimum angle for O1, based upon his years of experience.

    So, while a smaller clearance angle may well reduce edge longevity, as demonstrated in your study, we usually can increase longevity again by other means (such as a higher bevel, harder or more abrasion-resistant steel, etc). As in many things, guidelines are really compromises to deal with the range of variables usually involved in a given situation. While an ideal situation may exist, it may not be practical for all purposes.

    Regards from Perth

    Derek

  8. #8
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    Hi Steve,
    There is only one variable here. I sharpen at an angle (25, 28, 31, 34, 37) which mathematically give the clearance angle (20, 17, 14, 11, 8).

    As for a different bed angles, I don't know more than you or anyone else. It has to be tested. That being said and looking at the graph in the first post, a 25° sharpening angle is better than 31°. This bring me to believe that, if we were to test a bed of 38° then a 25° sharpening angle would be best. For a bed at 50° I would sharpen at around 30°.

    Pat,
    The width of those micro-bevels are not important. What's important is the last micro-bevel angle so, yes, a final micro-bevel of 25° will give a CA of 20°.

    Derek,
    I've tested many different types of steels and they all behave the same way. I think that this is the greatest find of the study. Even the hardest steel PM-V11 is much better at a sharpening angle of 28° compared to 35° just like all the other steel.

    I have also look at your website and didn't find anything for you to say "I have demonstrated in my own research". I've found plenty of end grain study which is not the same as planing with the grain. Maybe I missed something so could you please give me a link to any study pointing toward sharpening angles of 30 or 35 degrees.

    Normand

  9. #9
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    Derek,
    I've tested many different types of steels and they all behave the same way. I think that this is the greatest find of the study. Even the hardest steel PM-V11 is much better at a sharpening angle of 28° compared to 35° just like all the other steel.

    I have also look at your website and didn't find anything for you to say "I have demonstrated in my own research". I've found plenty of end grain study which is not the same as planing with the grain. Maybe I missed something so could you please give me a link to any study pointing toward sharpening angles of 30 or 35 degrees.


    Hi Normand

    The studies I did involved endgrain. The planes were shooting planes. One had a clearance angle of 12 degrees. The other had a clearance angle of 33 degrees. Both planes used A2 steel. The plane with the 12 degree demonstrated a significantly greater edge longevity than the plane with a 33 degree clearance angle, even when there was a higher bevel angle in the latter (30 degrees vs 25 degrees):

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

    Issues of clearance angle on edge longevity should not be differentiated by the direction of the grain, only that the conditions are held constant.

    In a follow up assessment, where only the BD plane with the 33 degree clearance angle was used, it was demonstrated that PM-V11 steel had a significantly greater edge longevity at 30 degrees than at 25 degrees:

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

    Regards from Perth

    Derek

  10. #10
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    Hi Derek,
    I have to disagree with you. Shooting end grain is, IMHO, a completely different ball game for a few reasons:

    1. End grain involve a lot of impacts which are basically not present in planing with the grain.
    2. Kato and Kawaii have shown that planing against the grain (not end grain) does not wear the blade on the bevel side. This is an indication that grain direction have to be accounted for.
    3. End grain is hardly compressible. When planing such grain I think that a small clearance angle should be better because there is no or very little wood springback (this is why we need a clearance angle) and, a large sharpening angle, as you have demonstrated, reinforce the edge.

    Normand

  11. #11
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    Hi Normad

    Good work. Something else to add, did you work with fine shavings and light cuts or did you also take deep cuts too? My gut says in deeper cuts the edge could perform less well as the support is not as great.
    Also did any of the work have hard dead knots often found in pine? The hardness of those knots and the speed that there are hit (often quick as the pine is so easy to work until you hit one) would make edges with a lot of clearance more likely to fail. Also, as mentioned about end grain a touch less clearance would be better as the work is more abrupt.
    I think it's likely why the typical angle of 30 degrees is so popular as it hit the mark as a great all round edge for a wide variety of tasks rather than having lots of plane irons or planes set with different clearance angles.

  12. #12
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    Quote Originally Posted by Normand Leblanc View Post
    Hi Derek,
    I have to disagree with you. Shooting end grain is, IMHO, a completely different ball game for a few reasons:

    1. End grain involve a lot of impacts which are basically not present in planing with the grain.
    2. Kato and Kawaii have shown that planing against the grain (not end grain) does not wear the blade on the bevel side. This is an indication that grain direction have to be accounted for.
    3. End grain is hardly compressible. When planing such grain I think that a small clearance angle should be better because there is no or very little wood springback (this is why we need a clearance angle) and, a large sharpening angle, as you have demonstrated, reinforce the edge.

    Normand
    Normand, the main difference between end grain and face grain planing is that there will be less springback with end grain (this is the end result of the lower compressibility of end grain). Is this relevant? I could go off on a huge tangent about wear bevels, etc and their impact on edge longevity. What is relevant was that the planing conditions were held constant for the two bevel angles (25- and 30 degrees on the 45-degree bevel down LN #51). The differences in edge longevity are therefore a result of the bevel angle differences. That was my point - to illustrate that bevel angle is one factor and clearance angle is another.

    The relevance is that clearance angle and the bevel angle involve a compromise - a trade off - to obtain edge longevity.

    I look forward to seeing further tests by you at different bed angles.

    Regards from Perth

    Derek

  13. #13
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    Hi Graham,
    All the shavings were 0.002" thick but it's possible that very heavy cuts would require a higher sharpening angle...
    No knots at all in the wood used for this study. A knot is very hard and would require a high sharpening angle again. I seldom use wood with knots.
    You're most likely right that 30° is a very good angle.

    Have a good day,
    Normand

  14. #14
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    Normand, I think this is a great study. I apologize for being minorly critical but I think it is best described as a study of combination best clearance angle and blade angle with a given bed angle. I think it is possibly more useful in that context since that is the context we're all working in.

    I don't believe it possible to decouple all of the components, only two of three at a time.

    Your efforts are a wonderful contribution and thank you for taking the time and making the effort.

  15. #15
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    Quote Originally Posted by Graham Haydon View Post
    Hi Normad

    Good work. Something else to add, did you work with fine shavings and light cuts or did you also take deep cuts too? My gut says in deeper cuts the edge could perform less well as the support is not as great.
    Also did any of the work have hard dead knots often found in pine? The hardness of those knots and the speed that there are hit (often quick as the pine is so easy to work until you hit one) would make edges with a lot of clearance more likely to fail. Also, as mentioned about end grain a touch less clearance would be better as the work is more abrupt.
    I think it's likely why the typical angle of 30 degrees is so popular as it hit the mark as a great all round edge for a wide variety of tasks rather than having lots of plane irons or planes set with different clearance angles.
    Good point on knots. I usually sharpen 25ish degrees (Freehand, and a little convex, so the precise angle is hard to say, but if I put my plane iron or chisel bevel down to a flat piece of wood, it'll usually start to take shavings around 28 degrees). A week ago, however, I was planing some SYP from hell, which had the hardest knots I've ever encountered. Twice I sharpened, and twice chewed up my edge every time I hit a knot. I had to resharpen at 35 degrees just to get through that board.

    As with most things, I suspect there's no "best" angle, and it probably depends quite a bit on the kind of wood you're working, bed angle, etc. etc.

    Still, great work on collecting the data, though, and it probably offers a good starting point. I personally like to sharpen with a good bit of clearance, as I have actually had problems with too little clearance before. It would be interesting to see other factors tested, though gathering the data could be an endless quantity of work, ultimately.
    Last edited by Luke Dupont; 06-23-2016 at 3:01 PM.

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