Truck Pull

[murphy4trees]

If what stumper says is true... and it makes good sense the way he explained it.... There must be an optimal range of hinge thickness.... my guess is it would be about 10% of DBH... How about that .... now we know why.... I'd still like to sees ome experimentation in this area.. not sure how to set up a test..

 

[Stumper]

Daniel, Optimum hinge thickness as a percentage of trunk diameter-thought provoking. However, I think that we will find that optimum hinge thickness will remain under 2.5" without much regard for diameter or species.-The reason being the tendency of thick wood to begin rupturing wih a minimal bend. I posted above that I advocate hinges 1.5-2" thick. That is true but incomplete-I frequently use thinner hinges. I Usually use a 1.5+" hinge simply because I prefer to set my saw down and iniate movement with myself away from the stump. 1.5-2 inch hinges usually hold a balanced tree of moderate size until pressure is added to a tag line or a wedge is started (but moderate pressure will move them). If I'm just cutting 'till it goes or using a wedge but no pull line then I may cut the hinge down to .75 inch or even less. Hinges must not be made TOO thin. Paper thin/veneer thin hinges can collapse under the weight of the tree and relinquish all control. The question then becomes "How thick must a hinge be to withstand the pressures on it and not rupture until it is committed to its line of fall?" The answer is: "Not Very!" Compressive strengths of various woods vary widely but even relatively soft woods have longitudal compressive strengths in the thousands of pounds per suare inch range. (For example: Juniper can be compressed from the side with your thumbnail but longitudally it withstands about 6000 lbs per square inch of crush.) Big trees become somewhat self regulating since a one inch hinge in a 36"diameter tree still has thirty six square inches to resist crushing. In fact if total hinge collapse were a risk factor then wide, thin hinges would still beat thicker centerpunched hinges due to greater total area-In actual fact it is a non-issue so long as we don't foul up and cut our hinge down to nothing. Large diameter trees help us in another way also. If the trunk settles back,closing the kerf, a large tree will actually stress the hinge less than a skinny tree because the movement at the hinge will be less-the trunk moves fewer degrees in closing the kerf due to the greater depth of cut.
Most of us have seen trees that started moving and followed the face with 3 inches of hinge still left but in most cases thinner is going to be needed unless a great deal of pressure is being placed on the tree in the direction of fall. Thin hinges hold the trunk on the stump longer. Thin hinges resist barber-chairing. Thin hinges are GOOD.:angel:

 

[ptar]

Nick typed:

Multiply this force by the height of the tie-in point (47 ft). The groundman created 4,258 ft-lbs. of force at the notch.
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To be accurate, this not a force but a bending moment.

"The groundman created a moment of 4,258 ft-lbs. at the notch."

 

[TheTreeSpyder]

i guess that upgrades my terminology of "first flexxing of hinge"!

But i think that none the less an important moment. The changing form standing to moving. i think that all the line pull before is pretty much a waste, save to stand ready to force the hinge stronger at that point in time. If no stall, i think line pulls after this moment weaken/speed hinge movement/support. i think this is a way that wedgeing to same direction can be more helpful, as it pushes to this moment, then stops (for tree lifts off wedge and push stops).

Of course at the notch (face) i think is actually at hinge. Within hinge i think that the support of the tensioned fibers x leveraged distance from pivot will equal the leveraged force of tree and your line pull. That is the tensioned/stretched/pulling fiber area of hinge matching the loading. But then the compressed portion of hinge(across the sea of Stumper's neutral fibers), acting as central pivot balancer for the leveraged load (tree and line pull) vs. the support (stretched fibers in hinge) to inherit the down pulls of each, but not side pulls of each(?); given any lean.

So if we said by way of example that all pulls were down, not forward or to the left etc.; it could be said that the hinge loading was 3x of that of the {existing tree leverage + line pull leverage}. For the strethed hinge fibers would have to match the loading to stand still under load, there must be this balance, movement comes at the upsetting of this balance, as tree will seek to be lazy and find another balanced, resting point. The compressed part of hinge would bear the weight of both legs of pull to it (load and support) like it was a pulley in the center of 2 balanced pulls. But....

Enter next variable... Due to the fact, that the CG of the tree, and the line pull having more leveraged distance to the compressed pivot of fiber than the counterbalancing/equivalent support (pull of tensioned fibers); the stretched fibers must have many times more pull to make up for less leverraged distance across stump than to height of line and CG. So, i think that places many more X the force in hinge; the hinge not getting enough credit, as the matching proposed previously is only an approximation of 1/2 of the compressed region of hinge's work it does.

So the compressed portion still has 2x the downward pulls of leverage from lean and line, the stretched fibers have to have more power of resistance to balance against lean and line making compressed patchof fibers inherit the downpulls of both. :: Due to less leveraed multiplier on support side of equality than the load side, the stretched fibers must make up for the loss of the multiplier in higher pulling power than load side i would think.

We ask much from this wooden machine! So much that the hinge is a single use machine (generally) that is used till shorn and discarded giving all it could to the point of it's own demise.

Or something like that
(work in progress)
:alien: