Author Topic: The symmetric Sheet bend  (Read 30527 times)

xarax

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Re: The symmetric Sheet bend
« Reply #75 on: December 22, 2011, 02:19:35 AM »
   The second, less obvious security problem arises from slack shaking that causes looseness

   Could you plese elaborate on this a little more ? ( - because I think I do not understand this statement ). You mean the removal of slack during the dressing and tightening phase, or the possible generation of slack in a taut knot ? You mean the slack of the ends, or of the bights ? Is there such a "slack shaking" if the bend is kept tightened under constant load ?
« Last Edit: December 22, 2011, 02:21:09 AM by xarax »
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Mike in MD

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Re: The symmetric Sheet bend
« Reply #76 on: December 22, 2011, 07:47:35 PM »
Hi Xarax,

I just noticed that if you start out with my "small fancy bend" and pull out each working end one "step" (I don't know the technical term for a rope crossing), then it becomes a stable version of your symmetric sheet bend.  But if the WEs are shifted to a different orientation, then it unravels like a thief.

Mike

xarax

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Re: The symmetric Sheet bend
« Reply #77 on: December 23, 2011, 12:09:15 AM »
  Thank you Mike,

...if you start out with my "small fancy bend" and pull out each working end one "step" then it becomes a stable version of your symmetric sheet bend.

  Right. (I had not noticed that....) So, this points to yet another, (somehow indirect...) way to tie this bend !  :)
   What a difference a tuck can make !  :)
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xarax

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Re: The symmetric Sheet bend
« Reply #78 on: December 23, 2011, 02:50:12 AM »
  Ashley shows a number of "Single Carrick" mats, as he calls them, but not the mat upon which the symmetric sheet bend is based ... and I really wonder why. His ABoK#1440 mat is only a tuck different - in fact, it is quite easy to confuse those two ( I myself have confused them in my previous post, which I have edited now). Based upon this superficial resemblance, I call the mat that leads to the symmetric sheet bend "ABoK#1440 b".
   Now, I have discovered that we can tie the symmetric sheet bend starting from this mat, the ABoK#1440 b, - and not tying the Thief knot or the Sheet bend first, and only afterwards, by slight modifications of those bends, arrive at the symmetric sheet bend. I have tried this approach because I think we do not pay due respect to this genuine, elementary bend, if we tie it by first tying some other knot- similarly looking  but in fact do different, as the Thief knot or the Sheet bend. ( And because I was not able to follow the SS369 clever method... :)) So, I tied the ABoK#1440 b mat with kermantle ropes (as shown in the picture - notice that the openings are about one rope diameter wide), I closed my eyes, and then I start pulling the standing ends, slowly. Abra Cadabra ! The mat closed into a perfectly symmetric symmetric sheet bend, without consuming much of its tails. Some other time I had to hold the tails in place, by my thumb and index fingers, while I was holding the standing ends by my other fingers. I have discovered that the kermantle material has a kind of "memory', and if one keep tying and untying the bend with the same ends of the same ropes, these ends 'remember' , in some sense, the final form they had in the previous tying. So, it is easy to tie the bend again and again, starting from the ABoK#1440 b mat, and just pulling the standing ends, without even holding the tails in place.
   I take the liberty to ask the other members of the forum to try the same procedure, with the materials they use. I have no doubt that the method will not work with softer materials, and it will confront the peculiarities of the twisted strands of the laid rope. However, it would be interesting if it works with other materials than stiff kernantle- and I guess/hope it will work also for wire rope. 
   
 
« Last Edit: December 23, 2011, 05:41:54 PM by xarax »
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SS369

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Re: The symmetric Sheet bend
« Reply #79 on: December 23, 2011, 04:18:17 PM »
As far as the OP knot is concerned, to me at least, it does not matter what knot you tie to get to the end result because with other knots you will encounter equivalent tying along the way. I have tied it as the Carrick mat and as an additionally tucked Sheet bend, both end up as the same pre-tightened configuration. Also, I do not feel there is a need to tighten slowly by pulling the SP's, in fact I have repetitively consistent results in the "exotic" and not at all exotic cords and ropes by just yanking them swiftly apart.

And this does work with wire rope (1/16 inch) as I have indicated in a previous post and remains steadfastly intact under tension.

SS

Edited due to someone-who-sleeps-while-I-don't-s  edit. ;-)
« Last Edit: December 23, 2011, 11:08:48 PM by SS369 »

xarax

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Re: The symmetric Sheet bend
« Reply #80 on: December 23, 2011, 05:57:44 PM »
the Ashley drawing is not the same as what is being tied in the photograph.

  My dear SS369, we live in different continents, so I am sleeping while you are not !  :) The picture of the mat of the symmetric sheet bend I posted was correct - but it is based upon the mat I now call "ABoK#1440 b" - and not on the original ABoK#1440 ( as you rightly spotted ) ( I have edited my previous post, and, because I lost the original text somewhere, I had to re-write it from the beginning...Sorry, have another look at it, please)
   My point is that we can start from the "ABoK#1440 b" Single Garrick mat, and tie the symmetric sheet bend easily, without having to hold the tails not to slip while we pull the standing ends, iff we tie it with the same ropes and the same ends again and again, in a stiff material. It seems that some stiff materials "remember" the form they had in their previous loading -may be because they are temporarily deformed in some way -  and so they are easily, almost automatically driven to the same form they had taken previously. Had you noticed anything like this, with the plethora of materials you use ?

P.S. The ABoK#1440 "Single Carrick" mat is one tuck different from the symmetric sheet bend s mat, the "ABoK#1440 b"- so it is no wonder that it leads to the Sheet bend - which is one tuck different from its symmetric cousin.
« Last Edit: December 23, 2011, 06:23:37 PM by xarax »
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Dan_Lehman

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Re: The symmetric Sheet bend
« Reply #81 on: December 23, 2011, 07:34:46 PM »
Quote
E.g., I just pulley loaded (hmmm, 100# force?)
 [ in roughly 1/4" (6mm) laid + braided cords ]
a round sling joined with this knot & the zeppelin; now, I've
tied 25# barbell wgt. to the tail of the upper cord --which I
took to be the more vulnerable one--, and even with a small
drop of this load, the crusty old knotted rope holds; a few
more, bigger drops, and now the half-hitch form is pulled
out of position.  Going to the other tail seems more resistant,
but I don't want to attribute that to orientation vs. the ropes.
Note that in these tests only the tied-above SPart is under
tension, the lower SPart is free, and its tail is loaded, or
only the other rope's tail (& SPart) is.
So what size is this rope that endured a 100 lb initial loading
(if I'm deciphering you correctly)?  Do you really think that is
representative of common human strength setting of a bend
in either medium or larger-size rope? 

Touche' .  Trying the knot in 3/4" laid ropes (PP + Poly-Dac),
the exercise shows Roo's point --manual setting doesn't make
much difference to these particular not-so-flexible ropes.  Now,
it might be that some setting assistance is available in a device.
Or, maybe some knot-holding device is used (tape, seizing).
Again, I'm reaching for some use in which the knot's appeal
is (a) efficiency of material, (b) simplicity of tying (yes, with
some learning of setting/dressing), (c) relative strength (this
remains to be seen; I think there are issues that affect ...),
and (d) ease of untying (by hauling on ends, to capsize-loosen).
And against the better-known carrick bend, I think there's
an uphill battle.

Re (c), two issues --perhaps at times connected-- are the
*ambidextrous* nature (both-handed; which the Fig.8 has, too)
of the knot, and the potential for *race conditions* to lead
to imbalance in loaded geometry --i.e., one SPart stays
more straight than the other, sharply bent (which might
result from differences in surface condition --slickness).
Whereas the carrick bend has the SParts staying more
each-to-its-own-side business & formation; capsizing from
the lattice form can be problematic in mixed cordage, but
once dressed, loading shouldn't introduce biases.


  - - - - - - -

But to the issue of practical knots, I defend this knot's
presence under that title in that it presents a possible
joint, with the brevity of the sheet bend, square knot,
& grass bend
, which can be used for small tasks of little
consequence (albeit perhaps w/no more to recommend
it than *variety* --but maybe the forcible loosening ).
One could see all this captured under a theoretical remark
put under the ...Explorations... heading, too.


--dl*
====
« Last Edit: December 24, 2011, 05:34:23 AM by Dan_Lehman »

SS369

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Re: The symmetric Sheet bend
« Reply #82 on: December 23, 2011, 11:02:38 PM »
After reading the latest installments here I went to the shed and got an old worn and hard bull rope of .75 inches. I tied it using the method I have described earlier, all in hand and yanked it tight as I could fast. I did not fiddle with slow dressing as I don't seem to need to do this with this knot (even with the smallest of cords).
If I can get through my soggy yard in the days to come I will tie this in a loop fashion around a tree and using my truck I will see if it turns loose under a load that I can not approximate by hand and leg.

SS

xarax

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Re: The symmetric Sheet bend
« Reply #83 on: December 25, 2011, 08:16:23 PM »
   This bight can serve as a  rope-made pin for the "grenade"  :), that, if pulled, can release the corresponding tail, and untie thebend - as mentioned in Reply#53 (1). I can not predict if there will ever be a practical use for this trigger...but many quick-release mechanisms are utilized for safety/security  purposes.

1. http://igkt.net/sm/index.php?topic=3716.msg21551#msg21551

« Last Edit: December 26, 2011, 09:30:52 PM by xarax »
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Mike in MD

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Re: The symmetric Sheet bend
« Reply #84 on: December 26, 2011, 05:40:20 PM »
The symmetric sheet bend would be more stable with a Zeppelin-type tuck, although this makes the bend less simple.  The tucks also make the SSB look more like my "small fancy bend".  :) 

Mike

xarax

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Re: The symmetric Sheet bend
« Reply #85 on: December 26, 2011, 06:20:59 PM »
The tucks also make the SSB look more like my "small fancy bend".  :) 

  Yes, because we get fig.8 shaped links, and the bend becomes an interlocked fig. 8 bend (1). One tuck more, in a one-tuck bend, is too much , I am afraid !  :) On such simple a thing, adding something, however small,, is equivalent of subtracting almost anything else...because this bend has not much more, than its outmost simplicity.

1)  http://igkt.net/sm/index.php?topic=3148.0 

« Last Edit: December 26, 2011, 06:32:38 PM by xarax »
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xarax

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Re: The symmetric Sheet bend
« Reply #86 on: December 26, 2011, 10:45:51 PM »
   I have tied the symmetric Sheet bend and the What knot - GrassBend (ABoK#1406-ABoK#1490) with various elastic and springy  cords. Big advantage for the WhatKnot-GrassBend ! While the elasticity of the material tends to push the tails of the symmetric Sheet bend in the wrong  place, and the knot to degenerate into its evil impostor, it helps the tails of the WhatKnot-GrassBend remain in the correct  place - and the knot to close into the secure form, and not degenerate into a loose Thief knot. ( The springy elastic material seems to be at least as helpfull - and perhaps even more... - for the GrassBend, as the - commonly used fot this bend - flat semiflexible material.)
   So, if you have an elastic, springy material, you better tie the closest relative of the symmetric Sheet bend, the WhatKnot -GrassBend (ABoK#1406 -ABoK#1490). 
« Last Edit: August 09, 2014, 12:08:38 PM by xarax »
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X1

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Re: The symmetric Sheet bend
« Reply #87 on: April 24, 2013, 10:15:02 AM »
   The ingenious knot tyer Desmond Mandeville had found a way to arrive at the "Symmetric Sheet bend" ( which he had also met, and had named "Tumbling Thief" bend ) by a certain re-arrangement of a Carrick mat. See the attached picture. I have copied this image from the chapter " Trambles ", written by Geoffrey Budworth,  at : History and Science of Knots, World Scientific, 1996, p. 306
   In the same book, p. 316, one can find many references to Desmond Mandeville s work, some of which was published in Knotting Matters.
« Last Edit: April 24, 2013, 02:17:00 PM by X1 »

X1

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Re: The symmetric Sheet bend
« Reply #88 on: April 24, 2013, 02:16:34 PM »
I think that the method  "sheet bend adding a tuck'" is much easier

   There are many ways a knot can be tied, and the "Symmetric Sheet bend" / "Tumbling Thief bend", although the most simple symmetric bend possible, is no exception. The series of moves shown by Desmond Mandeville is not supposed to be an "easy" tying method, of course - it is a manipulation and transformation of one particular Carrick mat ( the a ) to another ( the e ). D. Mandeville had built a whole "mini-universe" of known and unknown bends, by performing similar manipulations / transformations. To be able to explore the hidden relations between apparently different knots, and arrive at any one of them starting from any other, by a series of similar "moves", seems fascinating to me. In a sense, all the thousands of practical knots are but a limited number of them, plus a certain sequence of such "operations". That is all what science is about, an effort to "reduce" the apparent multiplicity / infinity of phenomena to a small / limited number of simple "elements" - to "make everything as simple as possible, but not simpler". :)
« Last Edit: April 24, 2013, 02:30:54 PM by X1 »

xarax

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Re: The symmetric Sheet bend
« Reply #89 on: June 03, 2014, 06:27:47 PM »
   Two pictures of a Tumbling Thief knot, after hard loading : I use to haul a horizontal line taut by a Trucker s hitch, then step and jump on it, and then I repeat the procedure a number of times, until the nub of a bend in the middle of it becomes rock-solid... It seems that the more the bend is tensioned, the less vulnerable to any accidental release and "insecure" it looks ( even to people that do not understand how the friction between two adjacent lines is greatly enhanced by their local saddle-shaped deformations ), while the easiness of its untying remains exactly the same.   
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