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Thread: Tight mouths in wooden double iron planes.

  1. #31
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    Quote Originally Posted by Derek Cohen View Post
    I wonder what advantage there is with a smoother having a bed angle above 45 degrees if it uses a double iron? A lower cutting angle should produce a clearer finish. Bearing in mind that the lower the bed, and the more interlocked the grain, the greater commitment there must be to use the chipbreaker to control tearout.

    Two views of a 50 degree bed: for one building a plane for others, it offers a range of choices (i.e. to use chipbreaker, or not). On the other hand, if the plane is for oneself, the choice of the 50 degree bed angle is wishy-washy (sitting on the fence, so to speak). When I chose the frogs to keep in my Veritas Custom planes, they were 40 degrees (#7) and 42 degrees (#4). This was a commitment to using the chipbreaker.

    Regards from Perth

    Derek
    I don't think it's an either-or thing. Close-set cap irons and high bed angles mitigate tearout in slightly different way. I've seen pathological cases where I get small-scale tearout even with the cap iron set back by <8 mils (<0.2 mm). In those cases further increasing the bed angle helps.

    I suspect that what may be happening in those instances is that the fiber-to-fiber bonds in the wood are so week in relation to the stiffness of the fibers that even a very short setback creates enough leverage to tear the shaving out ahead of the blade. High cutting angles address this by "breaking" the shaving (converting it to type 2) at the point of the cut instead of several mils up the blade back. The downside to that is of course that finish quality is compromised a bit.

  2. #32
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    Quote Originally Posted by Patrick Chase View Post
    I don't think it's an either-or thing. Close-set cap irons and high bed angles mitigate tearout in slightly different way. I've seen pathological cases where I get small-scale tearout even with the cap iron set back by <8 mils (<0.2 mm). In those cases further increasing the bed angle helps.

    I suspect that what may be happening in those instances is that the fiber-to-fiber bonds in the wood are so week in relation to the stiffness of the fibers that even a very short setback creates enough leverage to tear the shaving out ahead of the blade. High cutting angles address this by "breaking" the shaving (converting it to type 2) at the point of the cut instead of several mils up the blade back. The downside to that is of course that finish quality is compromised a bit.
    Past testing I completed (others have done the same) reveals that one can combine the chipbreaker and (a high) bed angle to achieve good results. Still, as you note, quality of surface can deteriorate (- which is a very relative statement) as the cutting angle increases. I have had superb results on hardwoods, such as Jarrah, using a high angle BU plane. I have had a better finish off a low angle Custom #4 plus chipbreaker on softer woods, such as Tasmanian Oak.

    It is evident that one does not need to be black or white about the bed angle for certain woods. However, if one settles for one technique over the other (e.g. chipbreaker vs high cutting angle), then the plane design could include this (i.e. low bed for chipbreaker vs high angle bed without chipbreaker). It is not necessary to have both in one plane - unless you seek to offer choices (ala the Veritas Custom Planes). I did start with a 50 degree frog in the #4, and moved to the 42 degree frog when it became apparent that it worked better. I also continue to use a BUS at 62 degrees. It also works.

    Regards from Perth

    Derek

  3. #33
    I have claimed for years that the ideal bedding angle is somewhere around 40 degrees and that angles like 45 and 47.5 were used to give the craftsmen leeway to hone at higher or sloppier angles. Some craftsmen grind occasionally then gradually increase the honing angle over a period in order to speed honing, regrinding when the angle is too high. My experiments of forty years ago suggested that the clearance needed was in the 8 to 12 degree range.

    One fellow used to claim that the clearance needed to be in the 20 degree range. I wondered about this for some time until I saw him sharpen on a video. He raises the iron so much on the fine stone that he is honing around 40 degrees. A lot of guys say "just raise the iron about one degree, but when you watch they lift about seven degrees.

    I last had trouble with tear out in 1977. I would be suspicious of any claim that a high angle is needed.

    The mouth opening on my beech double iron trying plane is 1.85 mm (just over 1/16). The mouth is essentially the same as when I started using it in 1979. The wear is around 80 degrees. Some years ago a fellow claimed that if I looked in the escapement I would see all the scars from years of jam ups. He was in fantasy land; I can't remember clogging.

  4. #34
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    All this talk about tight mouths is mostly about cosmetics. To be usefull against tearout the mouth must be in the sub 0.2 mm range. We are talking here about mouths 0.5 mm wide and (a lot) wider. Another thing is, the sole of the plane must really bear down on the wood in front of the mouth. Even the slightest concavity here stops the tight mouth of being effective.

    A tightish mouth is helpfull to feel when the edge starts to poke through the mouth. That's usefull in use. And it makes it all a little easier to see when you peer down the sole to look at the projection of the edge.

  5. #35
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    All these angles aside, what is the "normal" mouth opening on the sole for a jointer...1/4", more/less?

  6. #36
    First question. I thought the cap iron effect did not require a small mouth, at all.

    2nd. Why not reduce the steepest part of the cap iron to a mere 0.2 or 0.3 mm. A tiny bevel. Everything above this could be a lesser angle, assisting escape.

    David Charlesworth

  7. #37
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    Yes David, we allready came to that conclusion, more or less

  8. #38
    Kees,

    I think this demonstrates an advantage for the new improved L-N chipbreaker. Also used by Veritas, IBC & Woodriver/Quangsheng.

    The bottom may be curved and a narrow strip, while the rest is low angle.

    I think I have noticed that a lot of old heavyweight irons, some laminated, for wooden planes, tend to have rather low angle cap irons?

    David

  9. #39
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    Nice thing about the old ones is the very gradual rounding. That looks great, and I just feel that it works a little better. But that's just supposition from me. Allthough the old ones look like they are very flat, they do tend to come out at 45 degrees right at the edge, unless some old joker made a mess of it of course.

    In a Stanley plane I perfer the original stle, because of the springiness. But they sure do need a lot of work most of the time.

  10. #40
    Whatever work is done by the c/b to the shaving, happens within a very small distance. Less than 0.5 mm ?

    David

  11. #41
    Quote Originally Posted by david charlesworth View Post
    Kees,

    I think this demonstrates an advantage for the new improved L-N chipbreaker. Also used by Veritas, IBC & Woodriver/Quangsheng.

    David
    They all look to me like they were designed by people who had no idea how to use a double iron plane. Maybe they could design an "improved" boomerang and sell it to tourists.

  12. #42
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    Quote Originally Posted by david charlesworth View Post
    First question. I thought the cap iron effect did not require a small mouth, at all.

    2nd. Why not reduce the steepest part of the cap iron to a mere 0.2 or 0.3 mm. A tiny bevel. Everything above this could be a lesser angle, assisting escape.

    David Charlesworth
    Are you trolling the forum now? :-)

    Seriously, your second question has been a topic of debate at least since I pointed out in one of my very first posts that the Kato-Kawai video shows the shavings deflecting within the first ~0.15 mm (and probably long before that - there is no such thing as a "new forum debate"). It was not favorably received.

    FWIW I think that 0.25 mm is plenty, and 0.5 is overkill. It appears that Kees has landed on the same solution.

    w.r.t. the first question I can only speak to why I've explored how small I can make the mouth while also using a close-set cap iron: I like to experiment, and one thing I like to experiment with is combinations of tearout control measures. The goal in this case is to see if adding a tight mouth enables me to (further) lower the cutting angle and thereby get a glassier surface. That's it, really. As with most experiments it's probably pointless, though I was pleasantly surprised at how low I could go with a properly shaped cap iron (<10 mils in some cases).
    Last edited by Patrick Chase; 03-02-2016 at 7:32 PM.

  13. #43
    Patrick,

    I see no Norse supernatural being under the bridge!

    I appreciate you comments about experiments. My own experience suggests tight mouth is the least effective method for reducing tearout. One of my planes has a 0.004" mouth. It works very well, but when faced with really nasty wood there is plenty of tearout.

    Did I imagine that people were saying that c/b setting was good when the shavings went straight up?

    Can anyone please direct me to the Kato Kawai video, preferably with subtitles, I can't find it anywhere.

    best wishes,
    David

  14. #44
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    Quote Originally Posted by david charlesworth View Post
    Patrick,

    I see no Norse supernatural being under the bridge!

    I appreciate you comments about experiments. My own experience suggests tight mouth is the least effective method for reducing tearout. One of my planes has a 0.004" mouth. It works very well, but when faced with really nasty wood there is plenty of tearout.

    Did I imagine that people were saying that c/b setting was good when the shavings went straight up?

    Can anyone please direct me to the Kato Kawai video, preferably with subtitles, I can't find it anywhere.

    best wishes,
    David
    Video here: https://www.youtube.com/watch?v=pdk4uRYioZg. There used to be a version with English translations on Vimeo and linked from David Weaver's article at The Other Site, but it seems to be gone now (broken link). IMO it's pretty easy to interpret the raw video, particularly because they present a dimensioned drawing of each configuration before they show how it works. The trick is to use the dimension they give you (cap iron setback) to estimate everything else.

    Based on the mechanics I suspect that close-set mouths may provide "tearout limitation" rather than "tearout prevention". If you think about what's happening when you plane with a tight mouth, you're relying on the sole to physically constrain the wood fibers so that they can't lift up ahead of the cut. The issue there is that you can't have a zero-width mouth, so it isn't possible to prevent them from lifting up at all. Unfortunately we don't have an equivalent of Kato-Kawai video with various mouth configurations so this is guesswork. I'm neglecting two big variables that I know of: The stiffness of the fibers themselves, which may prevent tearout beyond the mouth's edge. Also, the compressibility of the wood, which may allow tearout to propagate under the sole a little bit.

    IMO a straight shaving merely indicates that the shaving has been "broken" (converted to type 2). It doesn't indicate whether it was broken close enough to the cut to prevent tearout. In my experience you can get micro-tearout (fuzzy surface) as in the 0.3 mm case from the video and still have a type 2 shaving.
    Last edited by Patrick Chase; 03-03-2016 at 11:05 AM.

  15. #45
    Thanks very much.

    David

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