Author Topic: The symmetric Sheet bend  (Read 30523 times)

xarax

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Re: The symmetric Sheet bend
« Reply #45 on: December 21, 2011, 07:18:06 AM »
  The bend slows your fall by NOT holding, but rather slipping with some friction...   
   I may like to use this bend in an application where I intentionally want the bend to slip, but never in an application where I want the bend to hold securely.

   The bend will hold very well, I am afraid, and you will break your spinal chord !  :) This bend does not slip, because it is based upon a mechansm that uses shear forces ; the tails are squeezed hard by segments of rope perpendicular to them, segments that bite the tails hard, and do not let them slip.
   Before you jumb, spend some time, please, to read my previous, extensive posts, and try to see if I have any point that you just ddnt get. Also, I would be glad if you actually make some tests ( = experiments)  before you put your theory and your back on the line, like the ones I have made...because we all want you in one piece here !  :) :)

P.S. As I have said many times, I do not recomend this bend to people that had never understood or tied it correctly, and so they believe it slips. Moreover, I now tend to believe that this simple bend is like a simple mathematical theorem : one should  use it only iff he has understood its logic, but also one could  use it only iff he has appreciated its beauty.
   
« Last Edit: December 21, 2011, 07:37:35 AM by xarax »
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Dan_Lehman

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Re: The symmetric Sheet bend
« Reply #46 on: December 21, 2011, 07:53:58 AM »
It is the resistance of this pivot to shear forces, that ...
...Is no more "shear" than that of most(?) other knots,

   I use this opportunity to show another interesting bend (see the attached picture),
that can be used when we want to connect  two pieces of rope in a way that will allow
us to disconnect them easily, and then repeat the same cycle many times.

Yes, joining eyes with such inter-reeving is a nice solution;
I've played around with this in the same way --i.e., using
the eyeknots' tails--, and by using a separate rope for the
reeving.  (IIRC, someone published something like this in KM
many moons ago, and that inspired my search, later.)

BUT, trying this with some shopping-bag poly cord (the cheap
things put in clothing-store shopping bags, braided), I've had
the joint pull apart on me enough to lead me to want some
more reeving for any serious work.  --making a "square" pass
with each tail (i.e., a turn around the other eye's legs) and
re-tucking should suffice, and double the diameters in compression.

Quote
Now, this bend works exactly in the same way as the Zeppelin bend, ...

Actually, if the zeppelin is left a bit loose, there will be more
tension on the tails than in knots where those surrounding
bights/turns are interlocked (compressing the tails within);
this is readily seen in the sheet bend as it shifts under load
(i.e., the "same-side" (tails/SParts) version; the opposite-side
version remains more *square*, and seems less secure).

 - - - - - - -
Quote
I do not consider the Thief Knot "easy-to-tie" for the inexperienced knot tyer.
No, it takes some care in formation, unlike the lookalike
squaREef knot ; its "slippery nature" should be pretty quickly
apparent, upon trying to set the knot!

Quote
Those with experience are also likely aware that it is unwise to use a "binding knot" as a bend.

The thief isn't a binder, for sure.

Quote
Thus, we have the "Reef Knot" or "Thief Knot" and not the "Reef Bend" or "Thief Bend".
Hardly.  We have "fisherman's knot" and that's one of the most
common end-2-end knots around.  Let's not pretend that Ashley's
wish for "bend" use was or is as he desired.  --or that the supposed
dangers of the reef are a fact : that knot was for decades part
of some marine requirements, though I've heard rumor that it was
observed for a test and ignored in practice.  I've not heard actual
reports of its supposed dangers (unlike, e.g., many reports of the
problem of bowlines loosening & failing).

Quote
Let's set aside rope size and type for a moment.
I don't know how you can dismiss the security issue of the bend falling to pieces
if either or both of the free ends are so much as touched.
The free ends get snagged, stepped on, and dragged on terrain in real life

Or, let's not : it might be in some case of hawser-joining that
such an easily untied and material-efficient joint is desired,
for some momentary use (hence the desire to un-tie).  All
this fear of "falling to pieces ..." on mischief done behind one's
back, so to speak, is pretty much beside the point in such a
case (beyond SS369's rejoinder about how much more durable
his knots are than yours --maybe it's a question of the tyer?).
Now, I doubt that the carrick bend will lose ground to this.

Also, note that this knot is --as is the thief and it's more secure
cousin, the fig.8-- *ambidextrous* (er, both-handed) : for
laid rope, this means that there is a form-wise asymmetry to
the knot; a weaker & stronger side, likely --from the one SPart
turning with, and the other against, the lay of the rope.
(In braided rope we may not care.)

Finally, as for jumping 5 stories and expecting some frictional
magic out of a slipping knot, well, you must be working with
some strange physics on that.


--dl*
====
« Last Edit: December 23, 2011, 01:32:28 AM by Dan_Lehman »

xarax

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Re: The symmetric Sheet bend
« Reply #47 on: December 21, 2011, 08:44:42 AM »
double the diameters in compression.

  You mean, in resisting shear forces, double the rope-made pivot s diameter, double the number of diameters...So, I think that those kinds of bends should be tied only on relatively stiff, relatively incompressible material....Perhaps that is a part of the problem some people have when they try to tie the symmetric sheet bend ? ( I have not tried it with laid rope, to see if there are any noticable differences between S and Z ropes...I do not doubt that there will  be some differences indeed, but I can not even imagine if it woiuld be beneficial for this bend to have its tails resist to the further twisting - induced by the "cogging" effects -, or not !  :))

« Last Edit: December 21, 2011, 08:47:18 AM by xarax »
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SS369

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Re: The symmetric Sheet bend
« Reply #48 on: December 21, 2011, 03:54:54 PM »
Quote
I can think of a practical use for this bend.  Imagine you have two ropes.  You want to jump down 5 stories into water.  You want to slow your fall.  You also want to bring at least one rope down into the water with you.

Here's a solution.  You anchor one rope at the top where you are.  You tie this bend in the OP to join the ropes.  You tie the bend such that once tension hits this bend during your fall, the bend will operate to slow your fall.  The bend slows your fall by NOT holding, but rather slipping with some friction.  The bend comes apart as you near the water, and the lower rope comes down into the water with you.

This experiment could go horribly wrong if the bend actually holds!  So, unfortunately, this bend may also be a bad choice for what it does best.

(That's an idea for a new thread:  What are practical applications in which one would intentionally want a knot to slip?)

SS369, may I suggest you experiment with this rope in more types of rope?  Maybe try less expensive ropes that are more likely to be used in everyday tasks outside of climbing.  It seems like you're playing a little bit of the devil's advocate here.  That's useful to have another perspective, but it also makes you sound like you're a bit too far out there.

BOTTOM LINE:  I may like to use this bend in an application where I intentionally want the bend to slip, but never in an application where I want the bend to hold securely.


Quote
  SS369, may I suggest you experiment with this rope in more types of rope?  Maybe try less expensive ropes that are more likely to be used in everyday tasks outside of climbing.  It seems like you're playing a little bit of the devil's advocate here.  That's useful to have another perspective, but it also makes you sound like you're a bit too far out there.

Hello knot4u, I enjoyed your little story, but it is not anywhere near the case in my experience with this bend.

In my first post in this thread I wrote that I have tried this affair in cords and ropes from 3mm - 13mm diameters. I failed to mention the material and compositions, sorry. The ropes are varied in that regard, laid, double braided and kernmantle in cotton, poly( different mixes), nylon, etc. Since that writing I have tried repeatedly using more "exotic" materials such as stainless steel 1/16 inch aircraft twisted cable, 1/2 inch (twisted) manila, leather lace, tarred netting cord, hemp craft cord, 550 paracord, 1.4mm venetian blind cord, 10 lbs. monofilament fishing line and 1/4 inch chain. To date the only lines that gave me trouble tying were the chain and monofilament and that was in the tying.
Once tensioned they all held except for the mono and cheap cotton #72 twisted utility line that broke when I stressed it. I did not tension to breakage the leather or the hemp craft cord. The others I didn't bother to try breaking either.

I suspect that you are having a tough time tying this correctly and I don't recommend that you use this to ensure your safety when you "jump down 5 stories into water". You may do well to just jump with both pieces of rope however inexpensive they are.

Seriously now, I am not advocating the use of this exploratory bend for anything at all. I have only evaluated it for myself and found it to be as I have written. I am surprised that some have found it to be otherwise. I find it to hold well under tension and interesting that the simplicity of it works.

I suggest that the "average person" read the thread (including the opinions of the safety or lack of it), tie the bend, evaluate it for what it may be worth to them and do with it as They choose. I am under the impression that some people, members included, are here to learn things (and read some interesting ditties), discuss things and have a good time. I hope you are.

Bring to the thread your experience with this and other knots. Be sure to include a situation that you would like a bend to slip and perhaps we can help figure out what may be the best for that application.

As for being a devil's advocate, nah, not truly.

Sincerely.

SS

roo

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Re: The symmetric Sheet bend
« Reply #49 on: December 21, 2011, 05:26:06 PM »
I just now tied it again in 8mm rope( not all that exotic), tightened it up with a yank on both standing parts and then I kicked it and rolled it under my foot. It did not come undone.

So just touching, as you've indicated you can do causing it to explode, does not work for me. Perhaps I am naive in the magic arts.

As for anyone tightening "my bend" for me (!?). I think not.
I didn't ask you to step on the knot or kick it. Step on a free end while pulling!  You keep avoiding this obvious mode of catastrophic failure, and pretending it's a non-issue, as shown by your last line that indicates your willful blindness to this issue.
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roo

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Re: The symmetric Sheet bend
« Reply #50 on: December 21, 2011, 05:35:49 PM »
  All this fear of "falling to pieces ..." on mischief done behind one's
back, so to speak, is pretty much beside the point in such a
case
That "mischief" might just be someone trying to help.  And the complete degradation of the bend due to mild forces on the free ends need not happen "behind one's back" unless you think every snag, dragging, footstep and whip of a free end around an object occurs behind your back.  It's not a minor point, or beside the point.  It's the pin of this grenade.

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xarax

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Re: The symmetric Sheet bend
« Reply #51 on: December 21, 2011, 05:52:47 PM »
   I have tried repeatedly using more "exotic" materials such as stainless steel 1/16 inch aircraft twisted cable

  I believe that, if this bend will ever be used for a practical purpose, it would be most probably used on wire ropes - or on very thick, large diameter solid or double braided ropes. However, I myself have nor the tools and instruments, neither the knowledge and experience to perform tests with such "exotic" - but ordinary, every day life s nevertheless - materials. I am sure that the evil impostor of this bend, the "fig. 8 knot for cables and wires" (1) is, and would be very easily proven to be, inferior, by far, to the symmetric sheet bend... So, if the former is well known and utilized by the industry, why would the later remain totally ignored ?
  Now, the point made by Dan Lehman about this bend being (very ?) sensitive to the helicity/handedness of the laid ropes ( S or Z ), would also apply to the wire ropes.  I fact, with common two layer stranded wire ropes, the situation is even more complicated, as we have ordinary lay ropes and lang lay ropes...I have no clue how exactly, and how much, the particular helicity/handedness of a laid rope would influence the security and strength of a symmetric sheet bend tied on it, so the question about the two layer stranded wire ropes is rocket science for me... :)

1) http://igkt.net/sm/index.php?topic=3716.msg21487#msg21487     
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Dan_Lehman

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Re: The symmetric Sheet bend
« Reply #52 on: December 21, 2011, 06:05:57 PM »
  All this fear of "falling to pieces ..." on mischief done behind one's
back, so to speak, is pretty much beside the point in such a
case
That "mischief" might just be someone trying to help.
And the complete degradation of the bend due to mild forces
on the free ends need not happen "behind one's back" unless you
think every snag, dragging, footstep and whip of a free end around
an object occurs behind your back.
It's not a minor point, or beside the point.  It's the pin of this grenade.

I think you need to get out of your armchair and see some
real rope at work.  The scenario I hypothesized has to do with
stout rope in use, which doesn't brook of any "mild forces"
interruption.  E.g., I just pulley loaded (hmmm, 100# force?)
 [per Roo's note of omission : 1/4" ropes, laid + braided]
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.

Now, what I mused I think would see a carrick bend put in,
and the OP knot has an uphill battle to supplant that; but it
might, per some users.

--dl*
====
« Last Edit: December 23, 2011, 01:40:06 AM by Dan_Lehman »

xarax

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Re: The symmetric Sheet bend
« Reply #53 on: December 21, 2011, 06:06:03 PM »
It's the pin of this grenade.

 :) I like this metaphor. Actually, I think that, if this bend is really very easily untied - when one pulls the free end of one link towards the standing end of the other -, then this is a property of great practical importance ! A bend that can be untied easily, even while it is heavily loaded, is a very useful bend indeed. Roo, you are trying to persuade the members of this forum that this might be a practical bend after all, while I proposed to move the thread to our new 'Knotting concepts and explorations' forum !  :) I can even imagine some hunting and military applications based on this property (traps, etc.), so even TMCD would be satisfied. Brrr.... :)
« Last Edit: December 21, 2011, 06:33:00 PM by xarax »
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roo

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Re: The symmetric Sheet bend
« Reply #54 on: December 21, 2011, 06:29:46 PM »
I think you need to get out of your armchair and see some
real rope at work.
Here we go again.  Nobody in this forum does real rope work, except Dan. ::)

Quote
The scenario I hypothesized has to do with
stout rope in use, which doesn't brook of any "mild forces"
interruption.  E.g., I just pulley loaded (hmmm, 100# force?)
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? 

Either way, 100 lbs of intial load might be a great deal of initial strain for a tiny rope, or a negligible inital strain on a large rope.  I find that I can easily destroy the form of the bend with forces on the free end in the high ounces to low pounds range after a typical setting load in small rope.   I estimate it's closer to the ounces range.
« Last Edit: December 21, 2011, 06:34:08 PM by roo »
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DerekSmith

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Re: The symmetric Sheet bend
« Reply #55 on: December 21, 2011, 06:34:28 PM »
I can think of a practical use for this bend.  Imagine you have two ropes.  You want to jump down 5 stories into water.  You want to slow your fall.  You also want to bring at least one rope down into the water with you.

Here's a solution.  You anchor one rope at the top where you are.  You tie this bend in the OP to join the ropes.  You tie the bend such that once tension hits this bend during your fall, the bend will operate to slow your fall.  The bend slows your fall by NOT holding, but rather slipping with some friction.  The bend comes apart as you near the water, and the lower rope comes down into the water with you.

This experiment could go horribly wrong if the bend actually holds!  So, unfortunately, this bend may also be a bad choice for what it does best.

(That's an idea for a new thread:  What are practical applications in which one would intentionally want a knot to slip?)

SS369, may I suggest you experiment with this rope in more types of rope?  Maybe try less expensive ropes that are more likely to be used in everyday tasks outside of climbing.  It seems like you're playing a little bit of the devil's advocate here.  That's useful to have another perspective, but it also makes you sound like you're a bit too far out there.

BOTTOM LINE:  I may like to use this bend in an application where I intentionally want the bend to slip, but never in an application where I want the bend to hold securely.

Hi K4u,

The point with this knot is that it does NOT slip - it is completely secure in the form presented in the op.

However, it is one of three configurations this knot can be dressed into, the other two both cog easily.

And this is another point - they do not slip, they cog, and with this knot it is rotational cogging as well as linear cogging.  Two things lead from this - first - both sides of the knot run (cog) through simultaneously, so if one end runs out first, the whole knot falls apart, irrespective of how long your descender cord is.  The second issue is that rotational cogging does as its name implies, it rotates the cordage, i.e. it twists it.  If this twisting gets too extreme the cord will twist up and lock its progress through the knot, effectively blocking your descent...

If the cordage was long enough to reach the ground, I would use a knot I would be prepared to put my life on - Carrick bend etc.  The point being made repeatedly is that this knot is dangerous.  I have to fully agree with Roo, there are so many ways this knot could be converted into a cogging form, it should never be contemplated  for anything other than a thought exercise on 'how knots work.

Derek

xarax

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Re: The symmetric Sheet bend
« Reply #56 on: December 21, 2011, 07:27:25 PM »
three configurations this knot can be dressed into.
  there are so many ways this knot could be converted into a cogging form

  Actually, there are many more incorrect ways one can dress this knot, but I will not enumerate them here. That is why the knot is difficult to tie, because the possible errors are many ! However, there is ONE way that is 100% correct, is nt it that so ?  :) ONE correct way that can lead to one secure knot - i.e., a knot that that does not slip-  is enough for me.  :) 
« Last Edit: December 21, 2011, 09:28:09 PM by xarax »
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SS369

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Re: The symmetric Sheet bend
« Reply #57 on: December 21, 2011, 07:32:42 PM »
I just now tied it again in 8mm rope( not all that exotic), tightened it up with a yank on both standing parts and then I kicked it and rolled it under my foot. It did not come undone.

So just touching, as you've indicated you can do causing it to explode, does not work for me. Perhaps I am naive in the magic arts.

As for anyone tightening "my bend" for me (!?). I think not.
I didn't ask you to step on the knot or kick it. Step on a free end while pulling!  You keep avoiding this obvious mode of catastrophic failure, and pretending it's a non-issue, as shown by your last line that indicates your willful blindness to this issue.

roo

Willful blindness is a bit dramatic in this particular post, don't you think? You're being a bit specious with me considering I do not give advise to use this bend. I believe you are making a exceedingly large issue of it by your continuing to pound away at the keys on it. It has been said already.

I have written that I loaded this bend with my own weight(175 lbs.), bounced on it using a foot loop affair and it held. The tails were approx. 3 inches long. I noticed no slippage and it certainly did not come undone. I believe this test, simple as it is, imparts more force on the rope than the method you've espoused here a few times (rods, foot and knees).

I have just now repeated the simple foot loop test and while suspended I gave one tail (longer now so I could wrap it around my hand) a tug and I stayed above ground.

I think that there a few bends and a few "secure" knots as well that fit your grenade pin pulling metaphor.

I kicked and rolled of my own volition. Sort of didn't think I needed clearance on that.

I like the fact that it can be spilled relatively with some ease when its load is released, just the same as the bell ringer loop can once you're done with, let's say, a truckers hitch use. Both hold while under loading.

I'll reiterate my experience. It holds loaded in the ropes and cords I used to evaluate it. It held in cords I would not use it with. I would not be using it for life endangering/rescue work! And it is an exploratory knot for the use of discussion.

As for using rope for real work (though that statement was aimed at Dan), I do use rope for work perhaps a bit more than most here. Yes, a presumption, but I feel justified.

As for my willful blindness, I generally do not have others doing my rope work or tie the knots I will be using unless I feel confident they know how and have shown me so. Occasionally I even teach someone a knot or two.

Would you feel much better if this thread was moved to the Explorations Board?

SS

SS369

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Re: The symmetric Sheet bend
« Reply #58 on: December 21, 2011, 07:42:18 PM »
And is this knot so difficult to tie??

If you can tie a sheet bend, do so relatively loose . Then take the wend of the uncrossed bight and insert it into the opening between the uncrossed bight's sp and the crossed bight where they are close, then grab the two sp's, nothing else, and give them a yank.

It is no more difficult than the sheet bend.

SS

Hrungnir

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Re: The symmetric Sheet bend
« Reply #59 on: December 21, 2011, 09:51:56 PM »
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.
I'm able to make the knot hold in 2mm polyester with this tying method. I'm not able to make the knot slip one bit by using arm power.

By pulling the working ends, I will hear a "click" and the knot capsizes into a form where I can pull the knot apart by pulling the standing parts.

As for a pin of the grenade, I would rather use a slipped sheet bend. If I have bulky working ends (example: tied stopper knots), then the knot can't be pulled totally apart. The sheet bend is also tried and tested for different sized diameters, different types of materials, one tuck simpler to tie, harder to tie wrong and the "pin of the grenade" is optional.

Quote
I would not be using it for life endangering/rescue work!
If you would not be using the knot for life endangering work, you should probably not use it where there's something of value involved either. Why risking damage on your car because of a failing knot, when you can use a perfectly safe knot instead?
« Last Edit: December 21, 2011, 10:00:28 PM by Hrungnir »