Author Topic: define (Read 5186 times)

KC · « **on:** January 24, 2016, 11:59:19 AM »

Basics

SS369 · « **Reply #1 on:** January 24, 2016, 08:40:51 PM »

Hi KC.

I am not of the opinion that the overhand stopper presents the best option. I don't like the "cork" action. Any knot pulled into the hole will add stresses and stands a chance (however remotely, thinking soft-ish media) of pulling through.
I personally like and use a stopper of the type that presents more surface area around the hole, for example the Ashley/Oysterman stopper (ABoK #526).

Also, your graphic of force on a loaded line doesn't seem to be quite accurate to me.
Yes, in a straight line load, all the fibers could be equally loaded, depending on the construction of the rope. If core and sheath construction, there will be differences.

Around a curved surface, the tighter radius inner fibers will still be loaded, albeit compressed, while the outer will be more in tensile stress.
The center fibers will be splitting the load between.
Just my opinion.

Thank you for the good graphics.

SS

KC · « **Reply #2 on:** January 25, 2016, 12:27:43 AM »

On the curve, i guess i'm dramatizing a sharp curve imagery of loading.
- i see some of your point here perhaps in less dramatic bends until you say compressed are working on target load.
.
In (mentally) defining the family of rope, web, chain, cable, fishline etc.
i find they all are max strength only at inline between the equal/opposites pulls;
and that they only really work in the tension/ not compression direction?
(can't use a rope for table leg/ compression unless frozen theory)
Can't use rope as a crowbar either unless frozen.
-so been defining this as a inline axis and only tension direction on that axis only device family of tools (in my head)
(and thus why i'm bouncing it around here to test and get different views, thanx)
.
Must there not be a twilight of not stretched nor compressed fibers ;
in between the day/night of compressed/stretched fibers?
.

.
stopper- here i can agree more, but then trying to start with basics.
As far as stress to the lacing i can concede as can compromise and complicate things.
But, then; in my actual use, these were emergency stops mostly at that point, and if anything was going to be pulled that hard in regular/predictable use would increase frictions (make Anchor or Halyard hitch instead of Simple Turn before stoppers) and and/or seize down; because it would be best if no stopper was pulled into the machinery so!.
But then perhaps that is max in my range of A)tasks and B) professional climbing/rigging lines 3/4" and under.
And too, why i'm here seeing if all this floats..
All in all dLehman's lesson to me on fig.8 was correct, and ovewrhand is a better basic stopper especially for beginning tyers.
But, i certainly will be adding Oysterman for comprehensiveness thanx!
.
i started drawing ropes again suddenly at beginning of year, things i fought before in the artwork, seemed to just flow;
kinda spooky though, cuz making a knot site of these things has been a bucket list item..
.

KC · « **Reply #3 on:** February 19, 2016, 11:00:53 AM »

Quote from: SS369 on January 24, 2016, 08:40:51 PM

Around a curved surface, the tighter radius inner fibers will still be loaded, albeit compressed, while the outer will be more in tensile stress.
The center fibers will be splitting the load between.
Just my opinion.
SS

.
i keep coming back to this.
i think the proper model would be, that only stretched fibers carry load.
Any compressed or neutral fibers wouldn't be giving support.
.
The rope fibers would be said to be leveraged, fewer working to carry same load; increasing load on those working fibers.
.
Flat rope/webbing on same bend would nullify (d)effect by not having any real 'dimension' on the same bend; so no multiplier.
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On a smaller pulley, the outer/working fibers are the turn force then, and would calculate leverage over axle frictions from that point, not outer sheave.
Smaller diameter line not giving same efficiency therefore, and perhaps some slip if way too small to bed in sheave.
.
(some rope materials, like cable; take soft bight only, and specific shape sheave to support 'belly' of line in sheave, or fibers break)
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BUT, this isn't exact for kernmantle as stated. i always imagine kern as line and rest as window dressing afterwards/ after force model.

Dan_Lehman · « **Reply #4 on:** February 21, 2016, 07:15:57 PM »

Quote from: KC on January 25, 2016, 12:27:43 AM

On the curve, i guess i'm dramatizing a sharp curve imagery of loading.
- i see some of your point here perhaps in less dramatic bends until you say compressed are working on target load.

I'm unaware of anyone having used some clever force-modeling
program to try to illustrate what happens to cordage when bent
around a diameter,
but in my observations I note two things that run contrary
to the simplistic image cited :
1) fibres aren't strictly parallel to / aligned with the axis of
loading --except in the core of (rather specialized) parallel-fibre
kernmantle--; and
2) the breakage in a curved segment occurs on the concave
--i.e., inner, "compressed fibres"-- side of the cordage
(again, to the best of my observations, made of 3-strand rope
with 1-2 strand/s broken).

--dl*
====

KC · « **Reply #5 on:** February 23, 2016, 03:31:20 AM »

As rope threads thru or spirals on itself it is hard to tell everything.
But, geometrically by position the inner is compressed, outer stretched.
And seeing as webbing of same strength material, would have no real dimension on the curve, would have highest relative strength.
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i guess i'm not sketching so much any neutral /non-load bearing parts, that would just be spacers in this i'd think like kernMantle or a neutral core.
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3strand has it's own construction, was really aiming at general braids; but by position on curve will be compressed/stretched similar.
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Compression, drum damage etc. very real in lines, especially if deformed to flattening.
Compression damage / breakdown is a rope wear sign, as is friction glazing/fusing.
i'm not sure being crushed guarantees is load bearing in what i'd think is a tension only device; i think more in terms of rope becoming hard as rock and forcing remaining members to stretch over longer/harder distance.
Especially would note elastic nylon chain would have the elasticity on tension, not so much on compression side would go more to brittle fracturing of chain.

KC · « **Reply #6 on:** February 27, 2016, 11:32:13 AM »

This isn't a rope post, in the rope as a tool sense..
.
But rather a reminder of what can be done with the simplest of gear in a rope thread;
necessity being a real Mother, can birth many things!
Also, what secrets might be easily lost in time, but yet simply lay before us we don't see!
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This is 1 theory of pyramid building; simple tools applied for smallest effort leveraged to largest output (then drowned in effort multiplier).
i especially like how the weight of the load could be used to lift the ramp at each end of the cycle/return if can go a little past saw horse;
such self-working attributes allowing a much bigger scaling of whole scenario i'd think.
Loosing the knack to see and figure these things out is a loss of heritage(and awareness etc.) to the humane race;
things others have paid(some with thier lives) to lear nand tried to hand down; getting lost.
.

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Machines of rope, few pulleys etc. can do big things as well;
and then fold away into no real weight nor space,
like it was nothing and as if they were never even really there!
Rope/pulleys just need other (many times existing) objects for anchors and scaffolding.