Author Topic: The symmetric Sheet bend  (Read 30299 times)

Benboncan

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Re: The symmetric Sheet bend
« Reply #15 on: December 17, 2011, 05:53:11 PM »

Quote
It will almost never work for a flexible rope
I agree with this, it is useless in rope.
I wasn't suggesting it's use for anything else other than monostrand high tensile wire where it excels, it is of very limited use in mild steel wire even.
« Last Edit: December 17, 2011, 09:17:28 PM by Benboncan »

TMCD

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Re: The symmetric Sheet bend
« Reply #16 on: December 17, 2011, 05:59:31 PM »
I'm surprised that you would think this bend to be considered safe. They claim you should never use the square knot as a bend but I'd much rather use it than this mess.

In my failed attempts to secure it, hauling on the SE's by my three year old rendered it useless. You seem to have actually been able to secure it because you've been able to somehow roll the orange half hitch on top of the white half hitch and give it a VERY false since of security. I simply can't get that to happen in the various materials I've fiddled around with.

Speaking of bends, ABOK 1451 is a damn good looking bend and unties beautifully yet gets no praise around here. Ashley seems to like it.

xarax

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Re: The symmetric Sheet bend
« Reply #17 on: December 17, 2011, 07:37:21 PM »
I'm surprised that you would think this bend to be considered safe.

   I do not think, I know, and I can prove it experimentally  !   However, although I am disappointed for not been able to convey to you what I mean by those looong boooring posts, I understand you. Simple things are not easy, they are often more difficult and subtle than we think... I myself was amazed by how surprising safe and strong is this bend ( for ropes of the same diameter and similar material, as it happens with ABoK#1406.)
   It happens, even to knot tyers with great experience, to confuse matters, because, after a certain point, they tend to think of knots in terms of other knots, and lose the ability and will to think of knots as rope mechanisms, as structures made of simple knot elements. It is the economy of thought that drives them to this slippery road, where, when they meet a new - to them - thing, they run the danger of seeing past it.
   My dear TMCD, this bend has nothing to do with the reef family of knots in general, and the square knot in particular ! I had tried to explain it in looong previous posts...Ths bend is not working because of the friction forces around an embrace of two rope strands, that effectively blocks their motion relatively to each other and secures the tails. This bend is working because the tails are resisting to shear forces that try to bend them, as they are squeezed in between  segments of the two bights.

They claim you should never use the square knot as a bend, but I'd much rather use it than this mess.

   They are right. You are wrong.  :) This bend has nothing to do with the square knot, it is not a "mess", it is a marvellous rope mechanism that you have not understood yet, so you can not tie it...but I am sure you will, eventually, if you tie it correctly an adequate number of times.

you've been able to somehow roll the orange half hitch on top of the white half hitch

  Yes, because I tie it carefuly, knowing what I am doing and why am I doing it so, and I place the tails in the correct positions...You obviously do not follow neither my explanation of the working of this bend, nor my picture of the tightened knot, so it is expcted you will fail to tie it. I did not say that it could be easy, did I ? On the contrary, have stressed many times that it is a difficult knot to tie, because oftentimes the less is also the most difficult. However, do not confuse difficulty with insecurity ! There are many things and practices we use everyday that are difficult , but they are safe, if constructed and executed correctly. Do you think that an airplane is an easy thing to make or drive ?   Does it gives you a FALSE sense of insecurity ?  :)   
   It is amusing that I have compared this bend with  - and only with - the Whatknot (ABoK#1406) almost a dozen of times at those posts, but nobody has ever told a word about their relation ! I guess that people feel shy and uneasy to criticize anything that is in the ABoK, but enjoy  and feel proud to criticizing anything that is not !  :) However, everything that was said about this bend could have been also said for the ABoK#1406 and the ABoK#1875 as well.

   There are hundreds of good bends out there...That does not mean we will stop examining bends and their mechanisms ! I myself have written many things about the ABoK#1451 and its close relatives in this forum ( search the previous threads). I am not impressed by any interlocked overhand knot - based bend, ( with the notable exception of  this rope-made hinge, the Zeppelin bend ), probably because it is expected that, by using the amount of curvature those bends use, we will succeed to secure the tails. I am impressed by the simpler bends, like the ABoK#1406 and the Double Harness bend, because there is something unexpected, almost miraculous, in their efficacy. And the most amazing bend for me is this symmetric sheet bend, a beautiful little knotting jewel...that enlarges, by its mere existence, our view of what really is a knot .
« Last Edit: December 17, 2011, 08:44:06 PM by xarax »
This is not a knot.

roo

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Re: The symmetric Sheet bend
« Reply #18 on: December 17, 2011, 07:59:57 PM »
It may be topologically simple, but it's not simple to learn if you know what I mean.
Xarax won't like me saying this, but it's easy to make from a Thief Knot by shifting the ends, since the bend is just a deformed Thief Knot.  But this bend has bigger security and stability problems that have no cure.
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xarax

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Re: The symmetric Sheet bend
« Reply #19 on: December 17, 2011, 08:19:35 PM »
it's easy to make from a Thief Knot by shifting the ends

   True. This can be said also for the Sheet bend, and the evil impostor of this bend described in a previous post (Reply#14), In such a simple thing, even a miniscule change makes a big difference. In fact, this "shift of the ends" of the Thief knot produces an altogether new knot - that has no relation whatsoever with the parent knot, as I have tried to explain many times. The "new" knot works entirely diferently, and, if tied properly, of course, this bend is much, much safer than the Thief knot.   With yet another "shift", one gets the evil impostor, which, with ropes, do not work at all ! So, can we say that the symmetric sheet bend is a knot that is just a deformed unknot, as the evil impostor essentially is ?  :)

this bend has bigger security and stability problems that have no cure.
[this] bend is just a deformed Thief Knot.

   True. There is no cure for ignorance. If one does not understand this knot, he can not tie it. And if one believes that this knot is a deformed Thief knot, I am afraid that he has not understood a thing !  :) This phrase, "this bend is just a deformed Thief knot", (sic), made me lough loudly :)  !   Thank you, roo.
   
   True : A straight line is just a deformed knot, and a knot is just a deformed straight line. :) :) :)
« Last Edit: December 17, 2011, 08:46:27 PM by xarax »
This is not a knot.

roo

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Re: The symmetric Sheet bend
« Reply #20 on: December 17, 2011, 10:11:39 PM »
This can be said also for the Sheet bend,
False.  That would involve re-tucking.
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xarax

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Re: The symmetric Sheet bend
« Reply #21 on: December 17, 2011, 10:24:14 PM »
False.  That would involve re-tucking.
  No, It is true, because the false of a false is true... :) To  say that "the symmetric sheet bend is a deformed thief knot" was as false a statement as it could be...In fact, it was not even wrong, and I doubt that it was even a statement... :)
This is not a knot.

SS369

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Re: The symmetric Sheet bend
« Reply #22 on: December 18, 2011, 12:04:59 AM »
I have tried this simple bend in every cord and rope I have that I use for tying and evaluating new to me knots (3mm - 13mm).  It works every time I tie it and it is secure.

The way I tie it seems to make it form easier.

See if this works to make it easier for those who may be having a challenge.

Tie a sheet bend, one that has the WE's on the same side, and snug up it a bit. Then take the non-crossed bight's Working End and cross it over it's own Standing Part and insert it down through the opening between the SP and the other's bight. Pull slowly and final tighten.

In firm rope or cord like Titan 5.5 it holds, does not slip at all using my suspended weight and after setting the knot tight I can not shake it loose. It unties easily either by working the bights back and forth or if the tails are long enough, just yanking them.

*I would not and do not recommend this bend for any life endangering activities!*

SS
« Last Edit: December 18, 2011, 04:59:49 PM by SS369 »

roo

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Re: The symmetric Sheet bend
« Reply #23 on: December 18, 2011, 01:26:43 AM »
I have tried this simple bend in every cord and rope I have that I use for tying and evaluating new to me knots (3mm - 13mm).  It works every time I tie it and it is secure.

The way I tie it seems to make it form easier.

See if this works to make it easier for those who may be having a challenge.

Tie a sheet bend, one that has the WE's on the same side, and snug up it a bit. Then take the non-crossed bight's Working End and cross it over it's own Standing Part and insert it down through the opening between the SP and the other's bight. Pull slowly and final tighten.

In firm rope or cord like Titan 5.5 it holds, does not slip at all using my suspended weight and after setting the knot tight I can not shake it loose. It unties easily either by working the bights back and forth or if the tails are long enough, just yanking them.

SS
Holding under a static load or only when the knot is very tight is a very poor standard of security.  You seem to admit that any force on the free end makes this bend subject to catastrophic failure.

Describing this bend as secure is a good way to get someone killed, especially when bringing up climbing rope and talking about suspending human weight.
« Last Edit: December 18, 2011, 01:27:31 AM by roo »
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xarax

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Re: The symmetric Sheet bend
« Reply #24 on: December 18, 2011, 01:31:49 AM »
   Thank you SS369,
 
   This is a (rare) case where a video would be of some help, I think, because the exact way one makes those moves you mention, every little detail of the whole knot-tying gesture, matters a lot - given the simple and fragile nature of this bend.
   Try to tie it by manipulating the ends of a Thief knot - as roo seems to suggest - and see if it would be easy to you. I myself I am not accustomed to tie the sheet bend quickly, so I start from the beginning, I form one carefully sized bight, I keep the tail and the standing end of this bight crossed, perpendicular to each other,  between my thumb and index fingers, and then I work the working end of the other rope with my other hand through and around this bight, as tightly as I can. Much more naive a tying method than yours, of course...
    In fact, there is a number of different sets of knot elements  we can see functioning in this bend, the pair of the opposed half hitches being only one, the most obvious of them. I see this bend as a more economical, shortened Zeppelin bend, where some parts of the paths the working ends follow, in the Zeppelin bend, are now missing. However, the working ends make a similar journey through and around the knot s nub as in the Zeppelin bend, they just follow shorter paths ! The pair of the tails play here the same role as in the Zeppelin bend : together, they serve as the pivot of a rope-made hinge. ( In the case of the Zeppelin bend, we can actually watch this hinge mechanism more clearly, as we can make the two links of a lose knot revolve around the axially placed pivot ). That is why I say that this bend is similar to the ABoK#1406 and to the Zeppelin bend more than to the Sheet bend or the Thief knot. It is the resistance of this pivot to shear forces, that prevents the whole structure from falling apart. In the Thief knot, we have rope strands that embrace each other, and, as the bights get smaller and smaller, the friction forces get larger and larger, to the point the rope strands can not move relatively to each other any more. We do not have strands at right angles to each other, like we have at the symmetric Sheet bend. In the case of the ordinary Lapp knot and the Sheet bend, we have a mixed situation, something in between the Zeppelin bend and the Thief knot.
   Now, in this bend, as each tail is squeezed in between two rope strands, one from each link, they are safely secured in their position. Moreover, I think that a most beneficial thing is the particular way each tail meets the rope strand of its own bight - they are perpendicular to each other, so they bite hard the one the other, and the "dents" that are formed on their surface are deep and very effective in blocking their motion and preventing them to slide through the knot s nub.
  I could have described this bend as a more secure Thief knot, because the way the tails bite each other do make this symmetric sheet bend a knot much more efficient than the Thief knot, and the slippage of the tails much more difficult. However, I have not made the mistake roo did, and confuse a topologically similar knot, that could serve as a parent knot in some tying methods, with the outcome of those tying methods. We can tie this bend starting from the Thief knot or from the Sheet bend,as you describe,  but the end result is an altogether different animal, indeed. I have called it "symmetric Sheet bend" because the two links resemble the one link of the Sheet bend, but I could very well have called it ABoK#1406 b - as the ABoK#1406 is its closest relative, in appearance as well as in function.
   
« Last Edit: December 18, 2011, 01:56:49 AM by xarax »
This is not a knot.

Dan_Lehman

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Re: The symmetric Sheet bend
« Reply #25 on: December 18, 2011, 04:44:16 PM »
It is the resistance of this pivot to shear forces, that ...

Is no more "shear" than that of most(?) other knots,
such as Ashley's bend #1452 (or #1408).  Making
a big thing of this is misleading.  Tails are nipped, hardly
a unique quality; they have axial forces on them as well.

Quote
I have tried this simple bend in every cord and rope I have
that I use for tying and evaluating new to me knots (3mm - 13mm).
It works every time I tie it and it is secure.

That's a promising but strictly unhelpful comment --in that
we don't know what, exactly ... .  I'd guess that you have
paracord, which some have claimed won't cooperate?  (I
guess that I, too, have some, SOMEwhere, but haven't
yet found where.)  For getting close to that, I tried some
hollow-braid binding cord as is common w/commercial-fishing
gear, and it holds there as well.  It does take careful setting.
And after a fairly good stress w/the pulley (of a sling joined
by the knot), it did succumb to a tug on the tails to capsize
into the opposed-halfhitches form, from which it was then
loosened further.  That might be a reason to use this knot,
but I suspect most folks will prefer the carrick bend here.

A main challenge in tying the knot is getting the turn open
enough to correctly position the nipped tail, but open only
minimally, as best possible, to that the nipping doesn't
severely fold the tail into this turn --tricky balancing act,
as tightening the turn much will threaten to mis-position
the tail.


--dl*
====
« Last Edit: December 21, 2011, 06:33:50 AM by Dan_Lehman »

SS369

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Re: The symmetric Sheet bend
« Reply #26 on: December 18, 2011, 04:57:49 PM »
Quote
Holding under a static load or only when the knot is very tight is a very poor standard of security.  You seem to admit that any force on the free end makes this bend subject to catastrophic failure.

Describing this bend as secure is a good way to get someone killed, especially when bringing up climbing rope and talking about suspending human weight.

Hello roo. Your statement holds true for so many knots, bends and whatevers. A proper knot, for the most part, is one that is dressed to the point it needs to be. Some knots don't need much dressing to hold and some need quite a bit of fairing.

Do you use knots that are knot fully tightened regularly?

I have not suggested this exploration to be used in any manner, I have just iterated the materials I use for my own tying and evaluating.

Regardless of what you are driving at, I found this knot to be secure during the loading and during the flogging of it unloaded. It will stay tied under tension even using 1/16 inch aircraft cable.

I have not said that "any force on the free end makes this bend subject to catastrophic failure."
I did say, "It unties easily either by working the bights back and forth or if the tails are long enough, just yanking them." And this is a property of a good knot, the ease of untying."

Not all knots are best suited to all tasks and it behooves the tyer to be smart and pick wisely.

Under tension it is my belief that it would take a deliberate act to cause it to come undone. My impromptu test did include some tugging and bouncing which took it out of the realm of mere "static load".

No, I would not use it for life endangering activities. For those events I use other more proven affairs.

But that does not interfere with my desire to explore more  possibilities.

Did you find anything good about this knot?

SS
« Last Edit: December 18, 2011, 05:01:15 PM by SS369 »

SS369

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Re: The symmetric Sheet bend
« Reply #27 on: December 18, 2011, 05:23:34 PM »
Quote
I have tried this simple bend in every cord and rope I have
that I use for tying and evaluating new to me knots (3mm - 13mm).
It works every time I tie it and it is secure.

Quote
That's a promising but strictly unhelpful comment --in that
we don't know what, exactly ... .  I'd guess that you have
paracord, which some have claimed won't cooperate?  (I
guess that I, too, have some, SOMEwhere, but haven't
yet found where.)  For getting close to that, I tried some
hollow-braid binding cord as is common w/commercial-fishing
gear, and it holds there as well.  It does take careful setting.

--dl*
====

Hello Dan.

To list the sizes, materials and construction  of each of the various cords and ropes I have at my disposal is a task that I feel unnecessary without a direct question concerning it, but, I will for you.

Yes, I do have paracord. I have Lacrosse cross-lacing cord, accessory cord, prusiking cord and climbing ropes of many brands. Cheapo poly-something or other from the big box store, hollow braid as well. I have manila rope, sisal, hemp and cotton multipurpose (mostly #72). Even some macrame of varying diameters of some synthetic shiny fibers. And the list continues....

If you want more specified data, please ask. Perhaps in pm as to not dilute the thread any more.

The point is not what I have, but that I use a fairly varied small collection to tie and evaluate some of the knots I encounter here.  And that is what the "unhelpful" statement was saying.

Someone offers a tangle that looks interesting, I tie it generally using a select few of the materials available to me. If it has promise I take it to my ad hoc test facility. ;-)

SS

DerekSmith

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Re: The symmetric Sheet bend
« Reply #28 on: December 18, 2011, 07:10:39 PM »

snip...

 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).

snip...

Hi Xarax,

I would be happy to comment on this knot as it is truly an excellent example of cogging dynamics, and I agree with you that a simple knot is an ideal starting point to examine the machinations of a knot's workings.

However, This is the 'Practical Knots' board, and this is never going to be a 'Practical Knot' and I believe we have a duty not to promote it as such.

While I must agree with you that this exact form of dressing is strong and stable under load, it only takes a tiny tug on one of the ends to convert it into one of the two other massively cogging forms.

Even though it is one of the few knots which 'dresses itself' to the extent that it won't eat any of the tails as it is loaded, it is none the less only safe as a 'cerebral exercise'.  To suggest to anyone with less understanding of a knot's functionality than you have Xarax, is I believe, foolhardy and irresponsible.

To that end, if the topic finds itself over in 'cerebrionics' then I will be happy to fawn over it.

Derek

DerekSmith

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Re: The symmetric Sheet bend
« Reply #29 on: December 18, 2011, 07:14:36 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

The interesting usage brought to us by Benboncan has illustrated an important point reagrding 'cogging'


Knots which require a rotational element of cogging will probably lock up when made of wire because it flatly refuses to 'rotate' like cordage will.

Derek