Author Topic: A knot that can be tied while the line is taut.  (Read 13657 times)

blooop

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A knot that can be tied while the line is taut.
« on: March 07, 2013, 12:46:13 PM »
Hey, sorry in advance if this is not the correct place to ask this question but I don't really know enough about knots to research the right knot for this application. 

This is a diagram of the setup http://imgur.com/fNR371w.   

I need a knot at point 2 so that the wire in between 1 and 2 stays taut.

Thanks

roo

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Re: A knot that can be tied while the line is taut.
« Reply #1 on: March 07, 2013, 04:10:59 PM »
Is it OK for end 2 to go around, say the left side of the enclosure to meet back up with end 1?

Can you say what this setup is and what it's supposed to do?  Are beveled c-washers OK to use? ;)
« Last Edit: March 07, 2013, 04:23:25 PM by roo »
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knot4u

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Re: A knot that can be tied while the line is taut.
« Reply #2 on: March 07, 2013, 04:24:45 PM »
Welcome. This is absolutely the right place to ask. That's an interesting problem. I'll wait for more info per Roo's questions.
« Last Edit: March 07, 2013, 04:27:05 PM by knot4u »

blooop

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Re: A knot that can be tied while the line is taut.
« Reply #3 on: March 07, 2013, 06:43:10 PM »
Thanks for replying!

No, it's not ok for 2 to meet back up with 1.    I drew this diagram is a simplified representation of the basic problem.  In reality I have 8 wires that are used to control a robotic tentacle. 

Here is a picture of the current solution for holding the wires. 
http://i.imgur.com/cygirwt.jpg

At the moment I am using a metal cylinder (black) with two screw to hold the wire at point 2.  This damages the wire and slips over time.  At the other end of the wire (point 1) I tied a knot so that it can't slip through the 1mm hole. 

I'm not exactly sure what a beveled c-washer is used for, but you can assume that even the smallest knot is big enough for it not to slip through. 

roo

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Re: A knot that can be tied while the line is taut.
« Reply #4 on: March 07, 2013, 07:37:38 PM »
I'm not exactly sure what a beveled c-washer is used for, but you can assume that even the smallest knot is big enough for it not to slip through.
Imagine two wedges laying on top of each other.  As you slide them together, they rise.

So you could tie a stopper knot using a needle to roll it up close to the hole, and then you could slip some custom slotted wedges under the knot to raise it up and create tension.

A hex headed fastener with a hole drilled down the axis could do the same thing (in a tapped hole).
« Last Edit: March 07, 2013, 07:47:08 PM by roo »
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Dan_Lehman

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Re: A knot that can be tied while the line is taut.
« Reply #5 on: March 07, 2013, 07:59:57 PM »
Given the fineness of your environment --the small material
and close tolerances, i.e.--, I can't imagine a knotted solution
to be adequate to your needs.  Your use of those clamps looks
excellent, and I will suggest that you simply try to use them
better --to wit:

1) tension the line and set the clamps tight,
esp. the away screw (i.e., the one nearer the end);

2) bring the line back over the clamp body,
past the away screw --perhaps make a turn around it--,
and then
2b) loosen the near screw enough to turn the line
around its shaft,
then tighten it down on this turn!?
(Well, clearly I'm thinking that the screw head of this
bolt is of greater diameter than the screw body.)

I'd think that this would suffice to preclude slippage,
while allowing fine adjustment; maybe it allows the
screw tightness to be relaxed enough to avoid damage
to the line?  (They look to be fairly kind clamps in this
regard; or could that be enhanced by some padding?)


One can muse about securing the lines to each other
or some part of the device (white plastic "X"s or the
center steel pole ...), but knots are prone to slippage
and yield under stress beyond what I'd think you get
in those clamps, and the risk of crimping the line by
knotting probably is as much a concern as whatever
damage the clamps do.

Another thought : can the ends of the lines simply be
brought back to turn around themselves between
clamp and abutting surface, as a lock against slippage?
Yes, that would entail inserting the 1mm diameter'd
material with effect on tension, et cetera (possibly
anticipated by lesser tightness in setting the clamps)!?

Admittedly, both of these wrap-the-cable-around-clamp
solutions risk bending the line over the clamp corners.

Maybe the simplest knotting solution is to turn the
lines around the white plastic *peninsulas* and then
tuck it beneath this turn (perhaps with a 2nd wrap &
tuck), sort of sheet bend, blackwell-hitch-like locking!?
(One need be chary of slippage from lack of sure nip
of a semi-flexible cord turning hard out of the hole
and over a flat surface (with wrapped tail to nip); a clamp
could be the finish, now needing less pressure for effect.)


--dl*
====
« Last Edit: March 07, 2013, 08:01:50 PM by Dan_Lehman »

knot4u

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Re: A knot that can be tied while the line is taut.
« Reply #6 on: March 07, 2013, 08:09:56 PM »
I'm not exactly sure what a beveled c-washer is used for, but you can assume that even the smallest knot is big enough for it not to slip through.
Imagine two wedges laying on top of each other.  As you slide them together, they rise.

So you could tie a stopper knot using a needle to roll it up close to the hole, and then you could slip some custom slotted wedges under the knot to raise it up and create tension.

A hex headed fastener with a hole drilled down the axis could do the same thing (in a tapped hole).

I am not understanding your description based on my understanding of a C-washer:
http://www.leansupermarket.com/servlet/the-80/C-Washer-changeover-setup/Detail


blooop

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Re: A knot that can be tied while the line is taut.
« Reply #7 on: March 07, 2013, 08:15:09 PM »
So you could tie a stopper knot using a needle to roll it up close to the hole...

http://en.wikipedia.org/wiki/Stopper_(knot

Which stopper knot would you recommend?

roo

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Re: A knot that can be tied while the line is taut.
« Reply #8 on: March 07, 2013, 08:34:37 PM »

I am not understanding your description based on my understanding of a C-washer:
http://www.leansupermarket.com/servlet/the-80/C-Washer-changeover-setup/Detail
See how it has a slot?  That slot would allow it to go around the line.  In this case, such a slot would have to be very narrow (probably custom).  The only other modification it would need is a cut or bevel to make the structure a wedge instead of a constant thickness. 

Also, it need not be circular in shape.
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roo

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Re: A knot that can be tied while the line is taut.
« Reply #9 on: March 07, 2013, 08:38:01 PM »
So you could tie a stopper knot using a needle to roll it up close to the hole...

http://en.wikipedia.org/wiki/Stopper_(knot

Which stopper knot would you recommend?
A simple overhand stopper would probably be the easiest to roll into position with the aid of a needle in the center of the knot. 

With this small stuff, I doubt you'll be trying to undo it anyway.
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blooop

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Re: A knot that can be tied while the line is taut.
« Reply #10 on: March 07, 2013, 08:41:04 PM »
Given the fineness of your environment --the small material and close tolerances, i.e.--, I can't imagine a knotted solution to be adequate to your needs.  Your use of those clamps looks excellent, and I will suggest that you simply try to use them better --to wit:

I am using metal part of block connectors at the moment.  http://i.imgur.com/vqu2z6k.jpg  They are very good because the screw diameter is large and they have a metal leaf that protects the wire from the turning screw face.

1.  I am already tensioning them to the point where it cuts right through the wire, and also the screw rips through the bottom of the clamp.
2.  Good idea, and although the screw head is larger than the shaft, there is too much space between the head and the clamp, so I can't clamp the wire in that gap. 

Maybe the simplest knotting solution is to turn the lines around the white plastic *peninsulas* and then tuck it beneath this turn (perhaps with a 2nd wrap & tuck), sort of sheet bend, blackwell-hitch-like locking!? (One need be chary of slippage from lack of sure nip of a semi-flexible cord turning hard out of the hole and over a flat surface (with wrapped tail to nip); a clamp could be the finish, now needing less pressure for effect.)

I like the sound of this but without the clamps.   I've looked up the blackwall hitch but am not exactly sure how it applies.

Here is a diagram of what I think you have suggested:  http://i.imgur.com/3RrSmYq.png

What would be a good knot to tie up the loose end to minimise slippage over time?

blooop

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Re: A knot that can be tied while the line is taut.
« Reply #11 on: March 07, 2013, 08:46:34 PM »
I've just realized that the fact that the underside is sloped may effect things.  This is what it looks like: http://i.imgur.com/IubQhF0.png

I also didn't mention before that I would like to move away from the clamps as they add weight, which affects the performance of the arm badly. 

roo

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Re: A knot that can be tied while the line is taut.
« Reply #12 on: March 07, 2013, 08:51:48 PM »
I've just realized that the fact that the underside is sloped may effect things.  This is what it looks like: http://i.imgur.com/IubQhF0.png
If that central compression rod was threaded, you could put a nut under that bracket to push it and induce tension in the lines with no additional hardware.

It may or may not be feasible for all I know.
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blooop

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Re: A knot that can be tied while the line is taut.
« Reply #13 on: March 07, 2013, 08:54:17 PM »
The central rod is carbon fibre.  The plastic crosses are all super-glued to the rod so its not possible to move them. 

alpineer

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Re: A knot that can be tied while the line is taut.
« Reply #14 on: March 07, 2013, 09:03:52 PM »
Stop!

Modify your (HDPE?) cruciforms with threaded holes to accept machine bolts spanning a slotted space which accepts the wire cable. The machine bolts will indirectly pinch the wire cable via the HDPE, and thus avoid cable abrasion. If you find it necessary to apply more pressure to stay the cable, use a nut on the end of the machine bolt. This will remove the stress from  the HDPE threads.