Author Topic: The symmetric Sheet bend  (Read 30244 times)

xarax

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The symmetric Sheet bend
« on: December 14, 2011, 07:17:16 PM »
   This is the simplest symmetric  bend I know - simpler even than the What knot (ABoK#1406), or the Double Harness bend. I believe that, if set, dressed and tightened carefully and properly, it is a safe bend with most materials. It would be interesting to compare its propertes with those of the more often cited relative, the What knot .
 
P.S. This bend was devised by Desmond Mandeville, and was named by him as " Tumbling Thief knot ".
See :
http://igkt.net/sm/index.php?topic=3716.msg27342#msg27342
http://www.surreyknots.org.uk/65-tumbling-thief-knot.htm
http://www.igktnab.org/km/KM10.pdf
 
 
         
     
« Last Edit: September 16, 2013, 07:06:19 PM by xarax »
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roo

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Re: The symmetric Sheet bend
« Reply #1 on: December 14, 2011, 07:59:18 PM »
I believe that, if set, dressed and tightened carefully and properly, it is a safe bend with most materials.
Any looseness allows the knot to fall into a form that readily rolls apart.  The same thing occurs if either of the free ends gets snagged.  Far from being safe, this bend based on the Thief Knot is not even remotely secure.
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xarax

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Re: The symmetric Sheet bend
« Reply #2 on: December 14, 2011, 10:06:17 PM »
  Thank you roo,

Any looseness allows the knot to fall into a form that readily rolls apart.

  The same can be said for the What knot (ABoK#1406). and, to a lesser degree, for the Sheet bend. This does not mean they are note secure bends...The great advantage of this bend is its outmost simplicity, and the minimum amount of rope bends.

this bend based on the Thief Knot

   Obviously  :), this bend is based on the Sheet bend...It is just as its name implies, a symmetric Sheet bend. I do not see any relation with the Thief Knot, figuratively or functionally. If we want to look for some bend that functions with a similar way outside the Sheet bend and the What knot, we might think of the Zeppelin bend. The tails of the Zeppelin bend work like the pivot of a hinge, they are loaded with shear more than with tension or compression forces.

Far from being safe, this bend ...rl] is not even remotely secure.

  I have tested this bend with many climbing ropes, and I have found that, on the contrary, this bend is very secure and very strong as well. I understand that, on a superficial examination, this bend does not look secure, because the public equates knot security with complex, tangled structures, and does not believe that so simple a form can be safe. Most known bends are based on interlocked overhand knots, so the fashion pays little attention to simpler bends - like the Double Harness bend, for example. I believe that knot tyers can go further than this...If you want a symmetric bend with a minimum amount of curves, this is the simplest bend you can find and use... provided, as I have stressed in my introduction, that it is "set, dressed and tightened carefully and properly". So, I can say that this bend is depending upon the properties of the knot tyer more than the properties of the rope itself :) That should be a blessing for the knot tyer that knows what he is doing and why he is doing this, is nt it that so ?
   I advice the members of this forum to study this simple bend, and try to explain its mechanism. We often believe we understand knotting, but our theories, or mental models, are not very satisfactory, and their shortcomings reveal themselves when they are confronted with simpler rather than more complex knot structures. When we attempt to explain a complex knot, we can hide our head under the sand easily, with a lot of blah blah. With a simpler knot like this symmetric Sheet bend, we have to understand more, to be able to analyze the less. Less is more difficult  :),  but not less safe or less secure!
« Last Edit: December 14, 2011, 10:15:55 PM by xarax »
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roo

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Re: The symmetric Sheet bend
« Reply #3 on: December 15, 2011, 12:03:53 AM »
  I have tested this bend with many climbing ropes, and I have found that, on the contrary, this bend is very secure and very strong as well.
You must not have a very high standard for security. 

I noticed that you've glossed over my comment about what happens when either of the free ends are snagged.  Have you tried this, Xarax?  If so, what happened?
« Last Edit: December 15, 2011, 12:04:27 AM by roo »
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xarax

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Re: The symmetric Sheet bend
« Reply #4 on: December 15, 2011, 12:37:01 AM »
I noticed that you've glossed over my comment ...

   I do not "gloss over comments" by anybody... :) I reply extensively and exhaustively in all comments made by everybody in this forum, (which is a rare thing nowadays... :)), to the point that my replies are often so long, repetitive and sooo boring...

What happens when either of the free ends are snagged.  Have you tried this, Xarax?  If so, what happened?

  I will answer to this question, even if it is evidently a rhetoric one.  It happens exactly the same thing as it happend with the WhatKnot (ABoK#1406) !  Is this a rhetoric enough answer ? :)
   Many bends are distorted when their free ends are forced to do something they are not planned to do... That is why they call them "free ends" in the first place !  :) It is expected that such a simple construction will be destroyed if its free ends change their position into the minimal knot nub that holds them fast. A simple knot form is more sensitive to even small changes than a more complex one. If the bend is held under constant tension, which is often the case in many applications, and if the ends are left "free", there will be no problem of safety or security in this bend.
   As I have said, we have to compare apples with apples, and this bend with the Sheet bend or the Whatknot (ABoK#(1406). Horses for courses.( My reply had touched a number of other points that I believe are also worth noticing   :)).
   It would also be interesting to try this bend with steel cables, or even electric wires. Besides having one only curve per link, it consumes a minimum amount of rope, a property that might be helpful in some applications.
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Hrungnir

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Re: The symmetric Sheet bend
« Reply #5 on: December 15, 2011, 12:10:55 PM »
   This is the simplest symmetric  bend I know - simpler even than the What knot (ABoK#1406), or the Double Harness bend. I believe that, if set, dressed and tightened carefully and properly, it is a safe bend with most materials. It would be interesting to compare its propertes with those of the more often cited relative, the What knot .     
I can't get this knot to hold at all in thin polyesterline (2mm). I'm able to pull the knot apart in one motion, even with super long tails. 

It's better in thicker polyester, but it's still suspect. It slips and stops when the the three-braided structure of the rope is messed up. You need to be careful not to tie this knot wrong, and when you tighten the knot you must pay attention so it doesn't form an unwanted structure.

The structure is very simple yes, just two half hitches. But you are also very close to a fisherman's knot.

xarax

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Re: The symmetric Sheet bend
« Reply #6 on: December 15, 2011, 02:57:10 PM »
   Thank you Hrungrir,

I can't get this knot to hold at all in thin polyesterline (2mm). I'm able to pull the knot apart in one motion, even with super long tails.  It's better in thicker polyester

  I believe that the problem with the small diameter cord you use, is that you can not manipulate carefully the strands in their correct position relatively to each other, because fingers can not handle such small diameter objects with the precision required here. So, I guess that the root of the problem is not the material, but the scale. I use kermantle climbing ropes 9 - 12.5 mm thick, that I can handle easily ( and I can see what exactly am I doing, without glasses :) ! )
  Now, pay some attention to this, please. This is not a bend that works like most of the others we know, where some bight shrinks, and nips a strand that goes through it, and, beyond a certain point, the friction forces prevent the slippage of this strand and secure the tail completely. The mechanism of this bend is depending upon shear more, rather than friction forces. So, if this bend is not set correctly at the first place, and taut in this place right from the beginning, it will not hold better at any time after this - because the pulling of the standing parts do not shrink any bight, to make the friction forces around a strand sufficiently strong to secure the tails. Pulling the standing parts further will make no difference, and an initialy incorrectly set bend - where the shear forces do not act properly as they should - will not hold at any time afterwards, however super long are the tails !  :) I believe that this peculiar property is the most interesting thing, because this bend, as I said, "is depending upon the properties of the knot tyer more than the upon the properties of the rope itself ". Read my lips : this bend works "if set, dressed and tightened carefully and properly". Try larger diameter ropes, and make sure you put the tails in the correct position relatively to each other, so that shear forces would have the chance to act, right from the beginning. Less is more difficult !  :) ( A fair price to pay). That is the nice thing with this bend : if one does not understand it somewhat, he can not tie it at all ! In other words, a blessing from the Knotworld for the knot tier.
   Try it with larger diameter ropes, make it hold before the final tightening, and you will see what I mean.

The structure is ... close to a fisherman's knot.

   No, not at all. The fisherman knot works in another interesting way : the volume of a stopper can not penetrate through a small diameter bight, because it is larger, bulkier than the diameter of this bight. The two overhand knots serve as two simple stoppers, and, as the tail of the one link goes through the nub of the other, they can not penetrate through each other. The stoppers are depending upon their internal friction forces to remain bulky and not degenerate into a straight line, which could  easily pass though. So, a fisherman knot will work, (although not with the same efficiency, of course) even if it is incorrectly tied, and we have only the tail of the one overhand knot going through the nub of the other. The fisherman knot is a superb bend, one of the best we have, just one click below the Zeppelin bend. However, it consumes a lot of rope, in a degree that we can say it is not economical... On the contrary, the symmetric sheet bend is the most economical symmetric bend there is and could be. However, it should only be compared to the ABoK#1406 and the Sheet bend, not to more complex, overhand knot based bends, like the fisherman s knot. Most of the bends based upon interlocking overhand knots work in this easy way we are accustomed to, where you set the bend and you just pull the standing ends until some bights get small enough, and the friction forces upon the penetrating the bights tails get larger and larger, and, eventually, the tails are secured. In short, set it and forget it...With this bend, you have to tighten it first, make sure the tails are at the right place relatively to each other, only then forget it. Something similar happens to the closest relative of this bend, the ABoK#1406, and also, to a lesser degree, to the Sheet bend.
« Last Edit: December 15, 2011, 03:10:08 PM by xarax »
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Hrungnir

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Re: The symmetric Sheet bend
« Reply #7 on: December 15, 2011, 07:33:42 PM »
Did you get your bend to hold when using two ropes of either different materials or of different diameters?


The structure is ... close to a fisherman's knot.
   No, not at all. The fisherman knot works in another interesting way :
That's not what I wrote at all. Re read the sentence from my previous post. What I meant is: you are only one step away from the fisherman's kot.

Have you seen the Double Harness Bend? http://www.Layhands.com/Knots/Knots_Bends.htm#DoubleHarnessBend

xarax

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Re: The symmetric Sheet bend
« Reply #8 on: December 15, 2011, 08:36:47 PM »
Did you get your bend to hold when using two ropes of either different materials or of different diameters?

  The material does not seem to matter. I have tried it with using many pairs of two different climbing ropes, which have different sheaths ( nylon, polyester, polypropylene, or a combination of them), and also different cores. However, their properties are more or less similar ( similar stiffness, for example ).
   I have not tried it with ropes of different diameters, because I think that its mechanism clearly dictates ropes of the same diameter. The same can be said about the ABoK#1406 - but not for the Sheet bend. Anyway, I see no purpose of wasting the advantages of a symmetric bend, by using it with ropes of different diameters.

Re read the sentence from my previous post. What I meant is: you are only one step away from the fisherman's kot.

   Ok. You wrote ;"you are also very close to a fisherman's knot."(sic), and I have misinterpreted it. Anyway, as I said, the fisherman s knot consumes a lot more rope than the symmetric sheet bend.
    In this sense, you are also one step away from the Zeppelin bend, which functions in a similar way, using the resistance of the rope to shear forces. The fisherman s knot works in an entirely different way, as I have tried to describe/explain in my previous post. 

Have you seen the Double Harness Bend? http://www.Layhands.com/Knots/Knots_Bends.htm#DoubleHarnessBend

  Do you mean if I have ever seen a Double Harness bend ?  :) It was in the ABoK, the last time I remember... I guess you have seen my post about it, at (1). I believe that the "short" Double Harness bend is, in a sense, even "simpler" a knot than the "long" one, but I can not explain this in a satisfactory way. As it is shorter, it is more compact, and looks more efficient. However, although it is a neat small bend, it can not be compared with the symmetric sheet bend in terms of economy and effective use of a minimum amount of material.

1.   http://igkt.net/sm/index.php?topic=2851
« Last Edit: December 15, 2011, 09:01:48 PM by xarax »
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Dan_Lehman

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Re: The symmetric Sheet bend
« Reply #9 on: December 17, 2011, 12:02:43 AM »
  I have tested this bend with many climbing ropes, and I have found that,
on the contrary, this bend is very secure and very strong as well.

!?  How on earth did you find it to be "very strong"?
--or secure, for that matter.  What were these tests
you claim?  --more than some suspended chair, I hope!

My surmise is that when push comes to shove, this knot
will show shortcomings for its brevity --esp. if the joined
ends are not equal in nature.  (The careful setting you
suggest implies some uniformity of behavior of the ends
upon loading, which might not be the case, for differences
of surface condition (friction) and elasticity & compression.)
I suspect the one end that might straighten more than
its opposite to lose necessary friction to stay tied.

Quote
If you want a symmetric bend with a minimum amount of curves,
this is the simplest bend you can find and use...

Actually, the squaREef knot is the minimal end-2-end joint
(and a good deal more use-tested than this).  It also has
an arguably better claim for being some symmetric sheet bend
--in that the original arose from bending a line to a clew,
essentially setting the nature of the bend as a hitch
where if symmetry were to be achieved it would be in
making the hitching line reflective of the clew.

As for material efficiency, I doubt that this knot has much if
any advantage in reality, esp. concerning its nature and one's
natural inclination to leave longer tails than one might endure
with something else, such as the dbl. harness bend .
There is a measure of consumed material in which one can
mark exit points of each part and then measure the material
consumed, and put it divided by rope diameter.  But this strict
measure omits consideration for material needed to effect (tie)
the knot, and of what might be desired as a safely long tail.
Even with the strict measure, though, I think that the above
knots will prove close.

Which is not to take away from the fascinating working/existence
of this simple knot --a late discovery for me (one that IGKT's late
Desmond Mandeville presented among his "trambles" through
the knotting universe, well prior my awakening to it).
--that subtlety of positioning the tails just so and TA-DA,
a joint is formed!!   :D  And it's one that "forcibly unties", per the
forces Roo notes --haul on the ends.


--dl*
====

knot4u

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Re: The symmetric Sheet bend
« Reply #10 on: December 17, 2011, 02:58:44 AM »
It doesn't hold for me in bootlaces and paracord.  Also, for such a simply bend, it's rather easy to tie it wrongly.  It may be topologically simple, but it's not simple to learn if you know what I mean.

xarax

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Re: The symmetric Sheet bend
« Reply #11 on: December 17, 2011, 04:22:15 AM »
   Thank you Dan Lehman,

  Which is not to take away from the fascinating working/existence
of this simple knot --a late discovery for me.
--that subtlety of positioning the tails just so and TA-DA,
a joint is formed!!   :D 

  I start from your last remark - which should have been the first, if your heart were as young as your brain. I am only an amateur neοphyte to the field of knotting, and it is natural for such a person to feel this awe for something that is so wonderful - almost marvelous - as a simple knot. However, when a veteran like you is also able to still feel the same thing, after all those years and all the unavoidable wear time imposes on things, this proves something about him, Ι believe, that should not go unnoticed. So, I take the liberty to repeat my call/request : Publish whatever you have in your notebooks, in an ordered and systematic way, if possible.

!?  How on earth did you find it to be "very strong"?--or secure, for that matter.  What were these tests you claim?  --more than some suspended chair, I hope!

 :) No, I have made some small steps beyond that stage, and I am performing more elaborate destructive tests, which I am going to publish in due time. I use a simple hydraulic truck jack, I measure the breaking forces, and I plan to test all the known bends, on a (cheap) 1/2 inch - 12.5 mm nylon rope.

if the joined ends are not equal in nature...this knot will show shortcomings for its brevity.

 I have not tested this bend s strength for pairs of different diameter or composition. As I have said, this is a minimal symmetric bend, and is expected to perform only with two ropes of the same diameter and of similar resistance to shear forces. I have seen that the surface friction characteristics, as well as their elasticity would not matter a lot - provided that are similar, as it happens with the most of the common materials. This is a knot that works using shear more than friction forces.

the square knot is the minimal end-2-end joint (and a good deal more use-tested than this).  It also has an arguably better claim for being some symmetric sheet bend

  Absolutely not ! The square knot works is using friction forces more than shear forces, as most bends do - with the exception of the ABoK#1406 and the Sheet bend. It is not the way we use the bend that relates it with the Sheet bend, but the way it works. And it works just like the ABoK#1406 and the Sheet bend, obviously. It would be nice if Derek Smith would join this discussion, with his explanation of the elementary knot mechanisms in general, and of the Sheet bend in particular. Given long enough tails, if we pull the standing ends of the  square knot, it will eventually lock, sooner or later. That is not the case for this bend, the ABoK#1406 and, to a lesser degree, for the Lapp and the Sheet bend(s).

Even with the strict measure, though, I think that the above knots will prove close.

  No, because the percentage of the difference, or the ratio of the required lengths, is relatively large and significant, given the small number that represents the length in the case of the symmetric sheet bend. However, I have referred to this property only in passing... It is the beauty of the minimal structure that is worth admiring here, not the economy of the material. I am glad you are still able to appreciate it, whatever excuses you use to "gloss over" this feeling... :) Knotting is more a mental game than a material necessity, and if we lose admiration and passion, we lose the better part of it - AND the desire to explore it further.
« Last Edit: December 17, 2011, 04:25:00 AM by xarax »
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xarax

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Re: The symmetric Sheet bend
« Reply #12 on: December 17, 2011, 04:37:25 AM »
It doesn't hold for me in bootlaces .

   It will hold only with material able to resist shear forces, and of circular cross section. That is expected because of the particular way it works, not because of its simplicity. The same will happen with the ABoK#1406, I guess.

Also, for such a simply bend, it's rather easy to tie it wrongly.

  Actually, I think that it is easier to do fatal mistakes in simpler things rather than in complex ones. If a thing is depending upon only a few elements and a few relations between thiose elements, even a small mistake is able to decompose the whole structure entirely.

it's not simple to learn, if you know what I mean.

   I may add that it is a difficult bend, a bend for the knot tyer, not the knot user, if you know what I mean. "If one does not understand it somewhat, he can not tie it at all ... It is  depending upon the properties of the knot tyer more than the properties of the rope itself ".
  Less is more difficult !  :)
« Last Edit: December 17, 2011, 04:56:04 AM by xarax »
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Benboncan

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Re: The symmetric Sheet bend
« Reply #13 on: December 17, 2011, 12:02:17 PM »
This bend is used extensively and successfully in high tensile wire fencing. Though this version is like a collapsed form of it. In fencing terms it is called a "figure 8 knot"  I have also heard "figure 8 splice" used, but never bend for some reason.

http://www.agf.gov.bc.ca/resmgmt/publist/300Series/307131-1.pdf


xarax

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Re: The symmetric Sheet bend
« Reply #14 on: December 17, 2011, 05:01:34 PM »
   The so-called "fig.8 bend for cables and wires " (DANGER) shown at (1) has no relation whatsoever with the symmetric sheet bend discussed in this thread. It works only because of the friction forces along the two end line segments of the tails. It does not use the resistance of the material to shear forces, utilised at the two crossings of each symmetric sheet bend tail - where the tail is squeezed in between two rope segments, the  strand of its own bight  and the strand of the other tail s bight.  In the former crossing, the two strands are perpendicular the one to the other, they bite each other, while at the second they move along a (short) segment of an helix, they embrace each other. The "fig.8 cable and wire bend" (DANGER) will almost never work for a flexible rope. In fact, it is the evil impostor of the bend we are discussing here. The symmetric sheet bend should always be accompanied by the skull and bones sign Ashley uses for ABoK#1406, but this "fig. 8 cable and wire bend" (DANGER) should be accompanied with something like the cross sign of a graveyard.  ABoK#49 and ABoK1875 show (a part of) the same mechanism of the symmetric sheet bend that is used by simple hitches. However, the whole mechanism of the symmetric sheet bend is more complex/subtle than this, as I have tried to explain by the reference to each tail resisting shear forces, induced on it by segments of its own and the other tail s bight.
   Although the evil impostor should never ever be thought of being used as a rope bend, the genuine symmetric sheet bend described in this thread will - most probably - work for cables and wires as well - and very effectively, I believe, ( I have not any knowledge and experience with cables and wires, so I could not test it with such materials - although I am very curious about the outcome of comparative tests, on cables and wires, between the genuine symmetric sheet bend and its evil impostor ).
 

  1)  http://www.agf.gov.bc.ca/resmgmt/publist/300Series/307131-1.pdf
   
 
« Last Edit: December 17, 2011, 06:26:00 PM by xarax »
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