What size of face cut?

[beastmaster]

I was wondering If there is a correlation between the size of your face cut and the force it puts on the tree when it comes off. Sometimes on a really dead tree I get nervous then I take a top or big chunk because it really shakes the sh_t out of the stick. If its narrow and comes off early does it push the stick back less the a 45deg or more cut would?

 

[wiltzzy]

face cut

beastmaster;
imho the size of the face cut [depth] is not as important as the amount of hinge wood that you have left when the break begins. I rely on @80% width face cut, a 5% or less side cut and a 10% hinge depending on relative fiber strength [deadwood or live tissue]. I seem to take the biggest rides with a narrow depth face and an early release. what say you all? Artistree

 

[True Blue Sam]

Ditto on enough hinge wood. I get called on some bad trees, sometimes just a shell, and you really have to size it up to place your hinge in the optimum spot for control. A natural flat face in the direction you want it to go is a blessing with a hollow tree.

 

[BarkBuster20]

Well as a rule of thumb i will do the face cut about 1/4 of the diameter of the tree at about 45 degree's of an angle and ill leave a hinge between a half inch to 3-4 inches depending on the size of the tree.

 

[Ekka]

Rule of thumb is 70 degree opening.

 

[outofmytree]

There is a correlation between the angle of the scarf and the distance the piece you are removing moves away from the stick. The higher the cut, or if you prefer the closer the angle gets to 90 degrees, the closer the piece lands to the stick.

I once blocked down a yard full of cocos palms and varied the angle to see just how much difference this makes. It was a very rough experiment but there was no doubt that the rule is correct.

My experience with sticks jumping back when taking out the top seems to relate more to the flexibility of the wood and how much pre-loading is applied. Whenever the top moves at a modest speed the resulting force is much less violent than when you set it up so that the top is ripped off at high speed.

 

[joesawer]

The face cut and hinge have everything to do with it.
As the top starts to tip over, it pushes the trunk back a little. Then as it moves forward it starts pulling on the hinge once the face closes. It pulls on it until it breaks. When the hinge breaks is when you get the sudden reaction.
The farther the top rotates the more momentem it gains, combined with a heavy hinge it can give a very strong whiplash.

 

[pdqdl]

I was wondering If there is a correlation between the size of your face cut and the force it puts on the tree when it comes off. Sometimes on a really dead tree I get nervous then I take a top or big chunk because it really shakes the sh_t out of the stick. If its narrow and comes off early does it push the stick back less the a 45deg or more cut would?

Correlation to force against the tree? Well, sort of, but not really. It does in small ways.

How wide open the face cut is made is will determine when the falling log/branch separates from the tree.

How much it shakes the tree is more determined by how much rotational inertia the branch has, how stable the spar is to oscillations, and what is the relative weight of the two separate parts of the tree.

When a tall section is cut away from a trunk, it pushes sideways against the spar as it is accelerated away from the tree. A short section of the same weight will not be accelerated as far to the side, so it will shake the tree less.

If you can cut a section away from the trunk and reduce the time that the removed section is pushing sideways on the spar, you will get shaken less. Salami cuts are very good for that, but you loose control of the top. Narrow face cuts, perhaps with a Humbolt-style face will cause the branch to separate from the spar sooner, thereby shaking the tree less. What really counts is how much rotation occurs before separation, and how much energy is transferred to the tree.

Also a factor: the speed of the release from the tree. A tall heavy dead section will have a lot of inertia during rotation, and will release and fall quickly. The same branch with all the leaves still attached has a lot more wind resistance, and rotates slower and releases from the tree slower. Less shaking.

Oops. Now you have to stop that falling section on the end of your bull rope. Lots more factors to weigh in here, mostly a reverse of all of the momentum incurred from cutting the section off. If the falling section is stopped in resonance with the oscillating spar, you get shaken off the tree. If it bangs back into the side of the tree as it is rebounding back from the push of the cut, it can stop the movement cold, leaving you with a big thump and not much motion.

Nobody ever talks about harmonic resonance in tree work here at AS, but it becomes terribly important on tall spars with no branches left on the tree to provide damping of motion.

 

[TheTreeSpyder]

i try to go about 1/3rd, then nip from sides; leaving stability, but as little wood to come thru to seperate as possible. We can always slow down cut, by backing foo the gas, but there is a ceiling on how fast saw will go, so remove some of the competition (fibers), to have more control.

Then, try to get a feel for when to get a quick release that the top's weight carries it away by it's forward force flow, without kicking back or pulling across spar as much. So if it is relatively soft lean towards target, but fairly straight up, i'll try to undermine the cg and get it to pivot forward, then quick release at/before about 1o'clock 30degrees. The reduced wood fiber, and the fast 020/200 can together give more control to orchestrate this IMLHO. the earlier launch allows the equal/opposit force to push more downaqrds the spar, instead of across...

Waiting too long for release can give a push back, or even later a pull forward at seperation i think.

On smaller/ higher tops if you do get some twang, try moving opposite of it, like throw bodyWeight forward as spar pushes back, and throw self backward as spar twangs forward. So that, you are dampening, not accelerating these forces. Similarily, when rigging out small tops, i might fall purposefully back into slacked lanyard (tightening it) with impact of body wieght backwards, jsut as top hits rope hard. You will be increasing the force on the spar, but lessening the leverge by ballasting the forward pull of the rig.

So, to me the answer is kinda setting it up right as you ask; but then a timing and body english to maximize etc.

 

[gitrdun_climbr]

I agree with 'face cut has everything to do with it'. On the ground when felling a spar I put as wide a face cut as I can so the hinge controls the wood till it hits the ground...some more fiberous trees will never break the hinge this way. At 100' in the air on a wobbly, stripped spar I bring that face cut down to the 50-60 degree range depending. This breaks the hinge most closely between the pushing and pulling stages putting the least amount of force on your spar. On dead trees, this could be the difference between life and death...it's good you're asking these questions. Degrees will also vary on how high up you are and whether or not you're trying land it flat to salvage a log.

Harmonic resonance really should be talked about. Here in PNW we find ourselves standing on 120' sticks with no brush or tops and that thing gets shakier than a whore in church!

Wonder if any of you purposely leave some brush on in those situations? Wonder how much dampening is lost by these guys running around selling 'wind thinning'.

 

[Hddnis]

I often leave three or four levels of branches at the top of tall evergreens to control shaking. It seems to act as a sail, also no doubt the mass comes into play. I'll clean out the branches on the side I'm dropping the top towards. This gives it a clear shot and keeps the rigging running smooth.

I vary my face cuts based on diameter and species of wood. I want a good clean break and sometimes I can get that with just a small notch. Set up on the hinge varies based on if gravity is doing the work of pulling the piece vs. ropes or wedges. I don't like it when a lot of force is required to break the hinge and so I set up to minimize that.

Another thing I've seen is a spar breaking where big branches have been removed. Because of this I often leave about a bit of the branch sticking out, 2-6" at the most. This retains strength over cutting the branches off flush with the main stem.


Mr. HE