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Thread: Skew irons for wooden planes

  1. #31
    You're most probably right. But in the woodworking world, a skew angle is suppose to lower the cutting angle. I would say if that is true, then the clearance angle is also reduced. So if the bevel angle can be regarded as just as robust and doesn't play along the same "rules", then we are still looking at a reduced clearance angle. And we don't want to skimp too much on that one. This thread started with a skewed plane with 38 degree bedding angle. That is allready on the bare limits of clearance angle, so when you reduce that even further, you have no other option then lowering the bevel angle.

    Hey, I'm just sparring some ideas. Fun to think about these things.

  2. #32
    Quote Originally Posted by Patrick Chase View Post
    All else being equal (cutting pressure etc) the durability of the edge is determined by its true geometry, not the cutting angle. The bevel is 31 deg in the example you give, period. We're not bending space-time here :-).

    Of course all else isn't equal because as you say "everything gets stretched out", but that helps edge durability for two reasons. First, as you point out the cutting angle is reduced, which lowers total cutting force. In addition, that cutting force is spread out over 1/cos(14) = 1.03X as much edge, so even if the total cutting force were the same you would still see a 3% reduction in cutting pressure (as I said in another post, you need more like 30 deg of skew to realize significant benefits from this effect).
    Per my last post, I'll stay away from debating physics. But I will say that your first sentence does not comport with my experience. A blade beveled at 30 in a common pitch plane will outlast the same blade bedded at 55 or 60, every time. I think this is a consensus opinion among people who have experience with a variety of BD angles (whereas it's not an issue for the BU folks, for obvious reasons).

    Side comment: It strikes me that some of the other commenters in this thread are not speaking from experience. Making a skewed bench plane is tricky; making one that performs well under the high stress of shooting, particularly when one is using a low angle that leaves zero margin of error, is even trickier. I don't doubt that Phil Edwards can do it (I have very high regard for Phil), but he has many hundreds of planes under his belt. His success may not be relevant or helpful to less experienced, amateur planemakers.

    A related issue is Derek's idea of rotation, rather than skew. I think it is a genius idea in theory, but if there is one thing trickier than skewing, it's rotation. Anybody here ever built such a plane (for example, a badger plane, which is both rotated and skewed)? It's a lot harder than it looks! I would not recommend it unless you've already built a lot of more conventional planes.
    "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

  3. #33
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    I have both 12-degree bed BU and 45-degree bed BD shooting planes with 20 degree skewed and straight blades, as well as a low bed (37 degree) BD strike block plane with a straight blade, and have completed a number of tests involving different steels and bevel angles. The references are available.

    Based on this I can state that the lower the bed angle, the less the stress on the blade. BU planes can get away with a 25 degree bevel, whether A2 steel or any other. By comparison, even PM-V11 is reduced to the ordinary at 25 degrees when used at a common angle (45 degrees) in a BD plane. 30 degrees is the minimum angle I would recommend in a BD plane. The low cutting angle benefit extends to the 37 degree strike block plane. A 25 degree bevel is quite satusfactory. 12 degrees clearance is more than sufficient - it is identical to the BU versions, such as the LV Shooting Plane and the LV and LN LA Jacks.

    Patrick, what I was referring to as fragile in a skewed bladed shooter is when the blade, per se, is ground at a skew since the wedge end will be weak. It is one thing taking very fine shavings on edge grain with an Edge Plane or a Skew Block Plane; it is another thing planing into endgrain on a shooting board. The former does not experience the impact of the latter.

    Regards from London

    Derek

  4. #34
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    Quote Originally Posted by Steve Voigt View Post
    Per my last post, I'll stay away from debating physics. But I will say that your first sentence does not comport with my experience. A blade beveled at 30 in a common pitch plane will outlast the same blade bedded at 55 or 60, every time. I think this is a consensus opinion among people who have experience with a variety of BD angles (whereas it's not an issue for the BU folks, for obvious reasons).
    How exactly do you think this contradicts what I said?

    I said "First, as you point out the cutting angle is reduced, which lowers total cutting force". That's exactly the same point you made above.

  5. #35
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    Quote Originally Posted by Derek Cohen View Post
    Patrick, what I was referring to as fragile in a skewed bladed shooter is when the blade, per se, is ground at a skew since the wedge end will be weak.
    This simply isn't right. There is no difference in the strength of the wedge end as a result of either skewing the edge or rotating the blade as you suggested. In both cases the effective geometry is exactly the same, with one exception: The very tip of the acute corner is somewhat weaker in a skewed blade, though that's irrelevant for shooting.

    You don't need an ME degree to see that (though I have one and was once a professional ME FWIW).

    EDIT : This assumes you grind to the same "true" bevel angle (as measured perpendicular to the edge) regardless of skew or lack thereof. Perhaps that's the root of the confusion?
    Last edited by Patrick Chase; 01-19-2016 at 2:44 PM.

  6. #36
    Quote Originally Posted by Patrick Chase View Post
    How exactly do you think this contradicts what I said?

    I said "First, as you point out the cutting angle is reduced, which lowers total cutting force". That's exactly the same point you made above.
    You said: "All else being equal (cutting pressure etc) the durability of the edge is determined by its true geometry, not the cutting angle. The bevel is 31 deg in the example you give, period." I understood that to mean that durability is determined by the (in this case) 31° bevel angle. It seemed clear to me, but if you meant something else, please clarify.

    Also, I did not take your comment above about lowered cutting force to be directly related to durability, nor should I--they are not equivalent.
    "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

  7. #37
    Originally Posted by Derek Cohen

    Patrick, what I was referring to as fragile in a skewed bladed shooter is when the blade, per se, is ground at a skew since the wedge end will be weak.
    Quote Originally Posted by Patrick Chase View Post
    This simply isn't right. There is no difference in the strength of the wedge end as a result of either skewing the edge or rotating the blade as you suggested. In both cases the effective geometry is exactly the same, with one exception: The very tip of the acute corner is somewhat weaker in a skewed blade, though that's irrelevant for shooting.

    You don't need an ME degree to see that (though I have one and was once a professional ME FWIW).
    This is boring. If someone were to come in and say "well Derek, I've used lots of shooting blades, both skewed and straight, and my experience is different," then I would listen. But giving everybody a geometry and physics lesson doesn't change the fact that Derek is speaking from (extensive) experience. I often disagree with him, but I respect his experience. I love abstraction and theory, but it's not worth a hill of beans if it doesn't comport with concrete experience.
    "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

  8. #38
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    Quote Originally Posted by Patrick Chase View Post
    This simply isn't right. There is no difference in the strength of the wedge end as a result of either skewing the edge or rotating the blade as you suggested. In both cases the effective geometry is exactly the same, with one exception: The very tip of the acute corner is somewhat weaker in a skewed blade, though that's irrelevant for shooting.

    You don't need an ME degree to see that (though I have one and was once a professional ME FWIW).

    EDIT : This assumes you grind to the same "true" bevel angle (as measured perpendicular to the edge) regardless of skew or lack thereof. Perhaps that's the root of the confusion?
    Substitute "pointy end" for "wedge end". I would have thought that was obviously what I was referring to (all bevels are a wedge, but ...) ...

    Regards from London

    Derek

  9. #39
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    This calculator lets you specify the mid angle, the tool thickness and the wheel radius and calculates 9 different heel and edge angles.
    http://www3.telus.net/BrentBeach/Sha...tml#grinderset

  10. #40
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    Quote Originally Posted by Patrick Chase View Post
    This simply isn't right. There is no difference in the strength of the wedge end as a result of either skewing the edge or rotating the blade as you suggested. In both cases the effective geometry is exactly the same, with one exception: The very tip of the acute corner is somewhat weaker in a skewed blade, though that's irrelevant for shooting.

    You don't need an ME degree to see that (though I have one and was once a professional ME FWIW).

    EDIT : This assumes you grind to the same "true" bevel angle (as measured perpendicular to the edge) regardless of skew or lack thereof. Perhaps that's the root of the confusion?
    Quote Originally Posted by Derek Cohen View Post
    Substitute "pointy end" for "wedge end". I would have thought that was obviously what I was referring to (all bevels are a wedge, but ...) ...

    Regards from London

    Derek
    But the topic of this thread was a wooden shooting plane. For the third time, the pointy end never touches wood in a shooting plane. It's irrelevant.

    EDIT: That point *is* a limiter in, say, a Skew Rabbet, because in that application it cuts the inside corner of the joint. Of course in that case you don't have the option of rotating the blade anyway (assuming you want a vertical sidewall), so it's a bit of a "take it or leave it" proposition :-).
    Last edited by Patrick Chase; 01-19-2016 at 7:08 PM. Reason: Tone it down.

  11. #41
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    The general direction of this thread remind me of the core reasons I moved away from making hand planes.

    Stewie;

  12. #42
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    Quote Originally Posted by Stewie Simpson View Post
    The general direction of this thread remind me of the core reasons I moved away from making hand planes.

    Stewie;
    Yeah, I'll back off now. I've pushed my point too hard. Sorry, all!

  13. #43
    Oskar,

    Check out Klaus Kretschmar's shooter part way down the page in the thread. I have read through most of this thread previously and believe that Klaus also built weights into the body of the plane for shooting. Nothing else to add other than an example of a skewed shooter if you haven't already been through the thread. Design also looks very similar to Stewie's plane which is a beauty as well.

    http://www.sawmillcreek.org/showthre...ild-Off/page17

  14. #44
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    Hi all, great response and interesting discussion. I've learned quite a lot from the comments. Thanks also for links on steel and and example planes.

    I will order a blade from Phil Edwards, its O1 steel, thick and a tested design. I have a lot of respect for the build, and I know it is tricky to get it right. This is however part of the joy, and I'm confident that I can cut a mortise and abutments with the required precision.

    Best regards,

    Oskar

  15. #45
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    Oscar. Have you considered the tooling your going to need to do this project.

    Stewie;

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