Author Topic: Looking for a one way adjustable/slipping stopper knot - if that even exists  (Read 8105 times)

mx066

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Dear all,

I'm looking for a knot but I'm not sure that kind even exists.

First of all I'm working with suture that is relatively small (braided type, between USP 2/0 and 3/0, i.e. between 8 and 12 milliinch in diameter). I have a kind of ring with an inner hole that is 1.5 - 2.5x the diameter the suture, sliding on the suture.

What I need is to stop that ring in one direction. I'm trying to do that with knot made with a second, independent piece of suture, a little bit like a bobber stopper knot would do (http://www.netknots.com/fishing_knots/bobber-stopper-knot/). The problem is that I need to be able to slide that stopper knot in one direction (relatively easily, i.e. with less than 1lbs force) and it must hold compression of the ring in the other direction (approx 2lbs force).

Unfortunately all the ones I've encountered, like the rolling hitch or the prusik, work in tension and not in compression. I currently have a workaround by using a common surgery knot, the roeder knot, but that requires a loop. Therefore I have suture running in the ring and out of the ring, which is not ideal.

I'm not sure where to start and doesn't even know if that's possible.

Any ideas ?
Thanks a lot !
Martin

roo

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Dear all,

I'm looking for a knot but I'm not sure that kind even exists.

First of all I'm working with suture that is relatively small (braided type, between USP 2/0 and 3/0, i.e. between 8 and 12 milliinch in diameter). I have a kind of ring with an inner hole that is 1.5 - 2.5x the diameter the suture, sliding on the suture.

What I need is to stop that ring in one direction. I'm trying to do that with knot made with a second, independent piece of suture, a little bit like a bobber stopper knot would do (http://www.netknots.com/fishing_knots/bobber-stopper-knot/). The problem is that I need to be able to slide that stopper knot in one direction (relatively easily, i.e. with less than 1lbs force) and it must hold compression of the ring in the other direction (approx 2lbs force).

Unfortunately all the ones I've encountered, like the rolling hitch or the prusik, work in tension and not in compression. I currently have a workaround by using a common surgery knot, the roeder knot, but that requires a loop. Therefore I have suture running in the ring and out of the ring, which is not ideal.

I'm not sure where to start and doesn't even know if that's possible.

Any ideas ?
Thanks a lot !
Martin
A secondary line may not be needed.  An overhand knot can be rolled into place by placing a needle into the largest opening of the loose knot.  Once the knot is where you want it, you pull the other end to tighten the knot and pull out the needle.

You can try rolling or translating a loose overhand knot with your finger to get the feel of it.
« Last Edit: April 04, 2014, 04:37:26 PM by roo »
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xarax

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   Try to use the Blackwall hitch, tied within a bight or ring ( i.e., not within a hook, as it is shown usually ). It forms a very simple one-way rope mechanism, because, when loaded, only the one leg can be pulled.
This is not a knot.

mx066

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Thanks for your answers !

I'll try to make a drawing of my situation later today. The problem is that I need the knot to be secured before adjusting it. The suture is intended to be dropped with the ring and the knot, and then afterward or even a couple of days later, we could come with a knot pusher and adjust it. That's why I'm looking for something that can be tightened beforehand and once in place adjusted several times.


SS369

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Hello mx.

I believe a graphic will help immensely.

The differential of moving force (1lbs. versus 2 pounds) may be a sticking point (no pun intended). The sliding stopper you gave the link to seems to serve the purpose you seek, sans different force needs, but let's see what the set up looks like.

SS

Edit: Adding this link to a previous thread with germane information. http://igkt.net/sm/index.php?topic=3659.0
« Last Edit: April 07, 2014, 08:07:17 PM by SS369 »

mx066

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Hi SS369,

It took a while, but here's a drawing of the setup. I hope that helps.

Thanks

SS369

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Hello mx066.

I still feel that the original sliding stopper you linked to is the type of knot that will do the task.
The real challenge is how to qualify it to a predetermined sliding value consistently. If you are indeed limited to exactly the forces you mentioned, then I believe there will be a need for some serious testing, and possibly a mix of materials.
I'm fairly sure that the suture manufacturers have the necessary facilities to do this, if not, there are independent labs for this type of thing.

It may be that the "washer" could contain the one-way locking and the knot just hold it there. An angled hole or a flexible constriction around the suture.  (?)

SS

roo

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Hi SS369,

It took a while, but here's a drawing of the setup. I hope that helps.

Thanks
Maybe you could have a V-shaped notch on the periphery of your washer.  That way, as you tighten things, you could wedge the line in the notch, and then for extra friction, you'd wind the excess line under the washer (maybe the edges would bend outward for easy winding).

If it works, it could be undone and re-tightened repeatedly.
« Last Edit: April 17, 2014, 04:40:58 PM by roo »
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Dan_Lehman

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I can't conceive of any knot mechanics that would
directly solve this problem --that pressure on the
hoped-for stopper would be like that on the adjustment
and simply push the knot, overcoming any resistance.
(One would need a friction hitch on the opposite side
of the pressured washer to resist --in tension-- the
load one direction and be adjustably pushed in the
opposite by the washer,
but this requires (a) fine enough yet capable line
to run through the washer from hitch to stopper, and
(b) room on this opposite/hitch side for that knot.)

--dl*
====

TheTreeSpyder

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Reverse Paradigm(edit: i guess same as dLehman):   

Friction Hitch above ring, ring pulls down on line to friction hitch to stop.

Push up on ring, that pushes into friction hitch coils to adjust/comb  friction hitch up the main support line(host to friction hitch).

Added Option: preset another small ring above friction hitch to adjust/comb friction hitch down the main support line.
« Last Edit: April 20, 2014, 06:25:45 PM by TheTreeSpyder »

Dan_Lehman

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...
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