searching for a self-tightening, locking knot for this application -attached img

[knothor]

Hello guys, this is my first post here please bear with me. I've been a fan of knotting for quite some time but never had the need to try more exotic knots. Now this need might have come and I need to be able to make a knot that allows me to tighten it by pulling one end of the rope and it should lock at the tightened position and not give back. I need this to tension a braided fishing line that is looped in a figure-8 pattern until the ends are close to each other. The attached picture would better explain my situation.

I actually need advice of a good way to do this too. I can use the bolts as pins to wrap a knot around. I am sure you will see more options than I do when looking at it.
I stumbled upon this knot called "Self-Locking Weston knot" that is used in surgery (http://www.youtube.com/watch?v=q_mLKmvoayI) but i've read that it is not a strong one.

Looking forward to read your suggestions.

[xarax]

   Your line seems a very slippery one - if the arthroscopic knots are not secure enough for your application, nothing will be, I am afraid... Regarding strength ( and not security / slippage ), the differences between various knots are not so great.
   The "Weston knot" ( ABoK#1991) is a very secure knot, because, even if it will capsize for a second time, it will settle in another also very stable form. Read about various arthroscopic knots at :
   http://igkt.net/sm/index.php?topic=4107.0
   
   A fine article on surgical knots :

   Locking, Jamming, and Ratchet Mechanisms of Sliding Surgical Knots Topologically Revisited
   J. Joris Hage, Lydia P. E. van der Steen     
   Journal of the American College of Surgeons
   Volume 205, Issue 5 , Pages 717-723, November 2007
   http://link.springer.com/article/10.1007/s00268-008-9904-2/fulltext.html
   ( You can download it for free from other sites ).

[roo]

Hello guys, this is my first post here please bear with me. I've been a fan of knotting for quite some time but never had the need to try more exotic knots. Now this need might have come and I need to be able to make a knot that allows me to tighten it by pulling one end of the rope and it should lock at the tightened position and not give back. I need this to tension a braided fishing line that is looped in a figure-8 pattern until the ends are close to each other. The attached picture would better explain my situation.

I actually need advice of a good way to do this too. I can use the bolts as pins to wrap a knot around. I am sure you will see more options than I do when looking at it.
I stumbled upon this knot called "Self-Locking Weston knot" that is used in surgery (http://www.youtube.com/watch?v=q_mLKmvoayI) but i've read that it is not a strong one.

Looking forward to read your suggestions.

Can you explain what is going on in your picture?  In the meantime, you can look over some options to see what best suits your needs:

http://notableknotindex.webs.com/Versatackle.html

http://notableknotindex.webs.com/slippery8.html

[Z]

I'd try these knots in this order:

1. Versatackle
2. Slippery 8
3. Arbor Knot

[knothor]

@roo: it's kind of hard to explain. This contraption is a double parallelogram whose main function is to ensure linear movement of the ends. Attached is an example of what this can be used for.

Basically the braided Spectra fishing line I'm using replaces a spur gear and thus avoiding any backlash. It can be taught as a lifting platform. I am trying to lift a weight of several kgs and I must tension the fishing line so that the joint moves symmetrically and smooth.

I will have another tensioning system in place but first I must close the loop as tight as possible so that the other tensioning mechanism can be used. That's why I need a knot that can pre-tension the loop and self locking to avoid any amount of give that would render the other tensioning useless.

I'm sorry if that's not clear enough. If needed I will explain further.

@Z: Versatackle looks interesting but to a untrained eye I can't really tell if this is the best. The amount of Spectra line that goes into that figure-8 loop is quite high (~3.5m) so I kind of have one shot otherwise I'd have to cut it and use another one. I don't think i'd be able to get a knot that can also easily untie as well as be self-tightening and locking. I am thinking that I somehow need to end up with an end that I can pull away while the loop tightens and locks, that's why the Weston Knot seemed a good choice.

BTW I am using braided (8 strands) Spectra 0.7mm that can withstand ~40kg (90pounds). I can't figure if the multiple figure-8 loops enhance in any way the tension this can withstand before breaking but I guess the few kg i'll have to lift will not exceed the rated values even in acceleration/deceleration.

Thanks.

[Z]

If I may summarize the requirements, it looks like you need a mid-air binder for tiny cordage (Spectra 0.7 mm, 8 braided strands). The working room between the ends appears to be about 2 cm apart.

[knothor]

Did a quick search on google for "mid-air binder" got to IGKT forums straight from the first page. Yes, basically the knot should not depend on the surface to be tightened but the surface is there if needed.

The distance between the loop ends is 2.3cm. I also thought of using the bolt in the immediate vicinity somehow but i don't know if that would help in any way. It might damage the spectra as the knot will be on the bolt's threads I guess.

[alpineer]

Hi knothor,
This type of knot is not likely to offer a satisfactory solution to your problem. I do though see a solution involving a permanent and strong knot, such as is used by fishermen to attach their lines, if you're able to modify the apparatus. You require a means of applying constant tension on your braided line with the ability to adjust the tension. Once tension has been adjusted it needs to be maintained by some type of spring loaded mechanism, as Spectra will creep over time when under constant tension. The tension adjustment mechanism and the tension maintaining mechanism could be, but don't have to be incorporated as one mechanism.

[knothor]

Hi alpineer thanks for your input. I was thinking of having this system to maintain good tension:

1) make a knot that will not give back after being made. If there is a chance that the knot tightens the loop the better;
2) there is a separate tensioning system embedded in the design, it's simple but effective: there is a tensioning block that goes over all the loops and presses them in the groove with a screw. I think the groove can be seen in the picture i took.

So far the Weston Knot, the slippery 8 and the Versatackle seem to be my best choices. Aren't they permanent?

Are you suggesting some other type of knot?

[alpineer]

Hi alpineer thanks for your input. I was thinking of having this system to maintain good tension:

1) make a knot that will not give back after being made. If there is a chance that the knot tightens the loop the better;
2) there is a separate tensioning system embedded in the design, it's simple but effective: there is a tensioning block that goes over all the loops and presses them in the groove with a screw. I think the groove can be seen in the picture i took.

So far the Weston Knot, the slippery 8 and the Versatackle seem to be my best choices. Aren't they permanent?

Are you suggesting some other type of knot?

  Yes, I did notice the groove with the hole passing through it but didn't quite make the connection, even though it's exactly the type of beautifully simple but effective mechanism that I was alluding to. I love it! Tell me, is there a means for maintaining tension within the system, should tension bleeding require frequent re-adjustment of the block screw? I'm thinking of a very stiff wave washer or coil spring at the head of the block adjusting screw.
 
  I have no experience using arthroscopic knots, so can't advise on how they might perform in your application. My concern is that this type of knot may bleed tension - over time - more than other knots. The proof, however, is most certainly in the doing. A backup knot(s) may be all that is required if material slippage is found to be a problem.
There may be benefits with this type knot if it can be cinched down progressively when required to give adjustment range back to the block tensioner. Of course, you can increase range by adding block tensioners at up to three more positions. Have you considered binding posts as a method for securing the ends?

Please do keep us informed of your progress.       
 

[knothor]

Spring Loading has been on my mind for some time but i must admit I am trying to avoid that as much as I can. But because it's a cheap and effective (moreover is tried and true) I might fall back to it. I will first run it without any such mechanism just to learn how the spectra behaves.

You kind of lost me in the lingo there, as far as i understand, backup knots are made after the main tensioning/locking permanent knot... so if this main knot slips a lot, the tension in the system would decrease to an unusable state with or without the backup knot. I am interested in a way to make for example another main knot just before the current one, thereby tensioning the loop again. But I don't think that is possible with a permanent knot.

Another idea would be to have one pin very close to the knot around which I can coil the loosen string should the tensioning block reach the botton of the groove. It would function like this: take out the block to offer enough slack in the loop to have it ran around the pin and then tension again. This procedure could go forever (or until the spectra breaks) and it seems such a simple solution. Even the first knot could be made to go around the pin, thus making it not a "mid-air binder".

What do you think? -of course I don't have such pin in my current design but heck a screw with a plastic sleeve would work until I redo the part-

[alpineer]

I will first run it without any such mechanism just to learn how the spectra behaves.

Exactly. There's no point in engineering something into a system if it isn't necessary. And you won't know that until you see how it behaves without it.

You kind of lost me in the lingo there, as far as i understand, backup knots are made after the main tensioning/locking permanent knot... so if this main knot slips a lot, the tension in the system would decrease to an unusable state with or without the backup knot. I am interested in a way to make for example another main knot just before the current one, thereby tensioning the loop again. But I don't think that is possible with a permanent knot.

A backup knot, for your application, is a knot which is tied directly on top of the main/first knot in order to keep the main knot from slipping any material. You can add them in series - one on top of the other - if more than one is required to mitigate slippage.

Another idea would be to have one pin very close to the knot around which I can coil the loosen string should the tensioning block reach the botton of the groove. It would function like this: take out the block to offer enough slack in the loop to have it ran around the pin and then tension again. This procedure could go forever (or until the spectra breaks) and it seems such a simple solution. Even the first knot could be made to go around the pin, thus making it not a "mid-air binder".

What do you think? -of course I don't have such pin in my current design but heck a screw with a plastic sleeve would work until I redo the part-

The idea of a binding post(s) was to create friction to help secure the loop and reduce the tension on the main knot.

[knothor]

Now that I understand what are they for I completely agree with backup knots. I will certainly include them.

I was explaining my idea of a post to spool around the creeped spectra line over time independently of your suggestion. For some reason I completely filtered that out from your message maybe because I didn't completely understand it. Are you saying that the main knot should be done over/around a post in the first place?

In order to take some tension off the main knot I could think of taking the loose ends and turn each of them around the post, thus making it easier to tie the knot. Is this in line with what you are saying? If not could you please explain more so I can visualize and get the right info into my thick skull.

Thank you.

[Z]

If you have a post on which you can start and end this cordage system, then your problem becomes trivial. However, I don't see such an option in the pics.

[alpineer]

  Are you saying that the main knot should be done over/around a post in the first place?
   
  In order to take some tension off the main knot I could think of taking the loose ends and turn each of them around the post, thus making it easier to tie the knot. Is this in line with what you are saying? If not could you please explain more so I can visualize and get the right info into my thick skull.

Imagine a separate binding post for each end to wrap around. Each end would take several wraps around its binding post, after which the ends could be tied together. This method isolates the knot from the higher forces that would otherwise be placed directly on the knot, and conversely isolates the remainder of the system from the strength weakening effects of the knot and allow the system to utilize more of the line's full strength because only the un-knotted line sees full tension.