Let's define our terms

[Mowerr]

Well, stepSon got an engineering masters degree, always figured should take some blame for that. He and his class/teacher re-affirmed many things that were questioned in early years here and elsewheres that i offered.
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As i chased and studied these things trying to feel them out and find the math that described; i found structural engineering/geometry/architecture inescapable. A tree is a large standing architecture, we take away some support and fold rest, sometimes making temp support structures of rope etc. to suit.
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i have worked and stretched brain to this, having to watch it like any other machine and back off and let it cool down at some points as you say. A different kind of climbing, but still you are your own coach etc. to meter what can take at a time and grow, not crush. But, now see these things echoed and re-affirmed in everything around; wondering how could have missed!
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To make it worse, "The Tao of Physics" was very formative for me, from my philosophy studies ( after some time in seminary, many parallels between Judeo/Chrisitan and Zen Sanskirt traditioons, but latter more towards understanding forces)way before all this. But still many problems that have sweated and turned over in over in head were resolved by slowing down and chasing yin-yang of the forces; where is that equal/opposite and how does it show up?
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i hated all that cosine/sine stuff in high school, even tho very good at math (teachers stopped my explanations, thru chalk at board and left classroom etc.). But now simply see cosine as the support column, and sine as anything else/it's non. It really helps to know these 2 'simple' things, and how they function in ALL of this! Like an electrical circuit, the direction of flow thru the parts can make all the difference. Many comparisons with electrical, hydraulic etc. forces. Part of believing can l-earn like this comes from most all electrical books at some point lend electrical force as water pressure etc. so have feel for electricity as force, from easier to visualize and feel water force as model. i carry many such comparative models in head to analyze and align with.
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Using own bod and trusting it , to read and learn forces for more of a body knowledge of this' knowing' that started to feel out in gymnastics to torque self etc. as needed for different effects; has been very helpful and constant companion. Kinda parallel to oriental mysticism of physical exercises to know and understand world after know self kind of 'body knowing'/achieved instinct (maybe). Working with trees has allowed me to see forces magnified like under a microscope; but also pushes you to that thin line between can and can't; and the large lessons of subject and self that allow you to push thru, that then can focus on as defining attributes.
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time fer work(was taught not really a 4 letter word)

I'd like to meet u sometime

 

[*useless info*]

ok!
Sorry for delay; deep in drawing think tank mode; but don't worry only publish half of it seems!
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Numbers allow us to weigh and measure etc. to help decode the world around us to better process and understand things. So, becomes the language of many things.
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The 2nd best selling MILLENNIUMS old text in the world of all time and likewise core of human thought and development stands as: "Euclid's Elements" (of Math, Geometry, Logic etc.)
>>#1 strategy of digestion and sorting; lists as:

"The technique of abstraction, based on ignoring physical considerations which are seen as merely incidental. Whether it was a rope, a piece of wood or any other physical object was irrelevant. It was all about properties of 'straight lines' connecting at angles, nothing more. These lines are simply mental constructs and the only entity necessary to the solution of the problem. The process of abstraction is about getting rid of all the nonessential elements and considering only what is fundamental."

i find the 'Pure Inline' mantra here too.
Seems like they were talking about us!
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Similarly; minimal device (or turns of rope) constructs give fewest points to evaluate and decipher to the tone of this abstraction premise.

 

[Bart_]

Hey Tree Spyder,
If you want to really mess with your combined mental models for systems consider the case of a rope like double braid and/or triple whatever like tachyon with its extra core and vary the load, pulley diameter (or rope diameter they're relative) like a pinto on a normal rope etc and then vary the pulley groove shape - now pick out the individual stress and strain on each fiber in the rope - the ones touching the pulley - ah it even changes as to where on the pulley you are - inner braid or twisted bundle core or even laminar core. I'll bet you a beer you'll feel like your head is going to explode before you can nail it down. Don't forget tightness/hand of the rope in question too. And fiber type. Dynema, vectran take a set, other fibers less so. Linearity shminearity! There might be something close to solutions to this hiding in the rope manufacturer's skunk works. Maybe the closest they ever got was finite element models. Don't forget the Poisson ratio.

Oh yeah, wash rinse repeat for a rigging ring aka a stuck pulley... or partially stuck..

 

[*useless info*]

These OSHA drawings shows some of my imagery/definition of Barber Chair; Especially Top-Middle ( i beleive these were dated 70's-ish ; now even this is old)

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Except would add the head clearance being impeded pushes back some and can get this folded back kill man standing behind/kickback action(and some from downward pressure on single spike), reminiscent of ol'barber chairs kind of action; but with seriousness of likewise breech side of rocket launcher; to the rear is still on the loaded axis!
(maintain same loaded axis released imagery working with loaded line, don't want to be on the loaded axis; anyone can become a bloody grease spot in a second!)
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i think Barber Chair mostly conjured by early close of face
>>ANY face close INSTANTLY reduces loading and gives more support in combined leveraged pulse backwards thru system AGAINST loading
>>Normal/later close of face guarantees tearoff by CoG great leverage, close across moving fibers, high speed (E=MCsquared is VELOCITY squared)
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An early close face IMMEDIATELY pulses back more support thru system , like ANY close
>>but breaks rest of rules, so as to not overload as fuse to positive tearoff/shearpin disengagement action against the sudden pulse of support
A>Early close leaves CoG with very limited leverage
B>Early close leaves tree still at slow speed
C>Early close leaves fiber angle more an unyielding column of tree over 'fa ce brace' than tree across
('face brace' stump block support of face that hinge folds into)
So, anyway has the same shift in gears that regular felling has enough to blow thru!
>>forces same hinge strength then greater strength at close, but with less loading against to nullify
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If hard compressed part of hinge and CoG weight/angle/length are the SAME forward positions;
the same forward resistance is mechanically forced from any hinge pattern(cut at same speed/not trying to trick) as a response. *
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So, early close of face, especially full across without relief to either side(as in Step-Dutchman) forces a column of downward force (overhead column fibers/not layed across), without enough leverage or speed to throw thru MECHANICALLY POSITIVELY/ CLEANLY ;like shear pin disengaging PTO drive from jammed parasite. It overloads and blows the mechanical fuse.
Early close doesn't have this shearpin safety
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A no face can give this in right conditions, perhaps easier to visualize. Kerf face could give just enough speed to make fierce column downward but not enough to throw across . Noobie HORIZONTAL bypass of cuts in rear of face, makes face within face and inner face controls mostly, as it closes early..
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The barber chair disaster happens like much else here, because we mechanically command it to; or perhaps simply don't insure and forge against it's perhaps constant risk! The machine logic code given, and Nature faithfully performs. Just remove some support to empower/start, rather than plug in.
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* We can spoof more needed support with wedge/rope (possibly vertical hinge bypass cut) FORWARDS ; then the spoofed need 'resolved'. for stronger hinge by spoofing greater need for greater hinge strength response back.








i make BIG distinction between HORIZONTAL bypass in face as across fiber close/up fiber column. vs. VERTICAL (slanted) cut bypassing as more between fibers and a close ACROSS fiber more properly. In general look for clean meeting joints of well machined face, perhaps sniped corners. Specifically NOT full face early impedance to folding/rolling forward of overwhelming and yet building more force!.

 

[Dave tettleton]

Can't resist the temptation stir the pot. We can add two more meanings to barber chair. Big horizontal limb, wood prone to shear stress failure, version one the branch "barbers" on the outboard section before the top cut finishes, version two the inboard section "barbers" with the outboard section staying intact before the top cut is finished. Then to mess it up more, what to call it when the wood is near 45 degrees, not vertical and not horizontal? You'd have to start thinking too hard about what a guy really means every time you heard the term.

Seems the term barber chair might get overused describing too many shear failures/splits.

I am thinking the term was made up when actual barber chairs were raised and lowered by mechanical scissoring pieces of metal before hydraulics or air. Am thinking it's the scissoring action that it's named after. Could be totally wrong tho