Why 1/3 notch depth?

For me the 1/3 guideline always mostly meant hinge fibers then start further than 1/3 back , and their tensioned backfield even further back, more into 1/2 way range for hinge of most width.
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Most width affording more side to side control, and a thinner/ more flexible hinge. Especially in the tension backfield vs. compressed pivot to CoG side of front fibers.
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Bluff hinge foward on hard forward lean, back on soft or back lean. On pure round each is probably at a loss of side to side control and further back makes CoG more towards target, but lose wedge leverage as lift or even safety backstop in trade/as stated. Each time chasing the CoG with compressed part of hinge as pivot. Stump is finite playground to align these choices on, capitalizing on the pluses as cap the losses that occur in trade, or even capitialize on losses and or their byproduct(s).
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If using shallow face in large tree would precut to triangle or strip back so final backcut is not too slow. May center punch face too, which also affords e-apportioning those fibers to sides for more steering control.
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Always favor Tapered Hinge as built in self adjusting ballast against side force until tearoff. Simply exemplifying the side control to a single 'off side'(Dent). Side force ballasted out of formulae allowing remaining forward force to more deftly carry the whole package home to target. Tapered vs Standard both fold at same forward resistance to same load, only Tapered reapportions to greater resistnce against cross axis pull of side lean. Even Tapered pointing downward against side load to mostly horizontal path on long horizontal limb can work this way. Dent's lil'drawings persist to be true, even at these angles.
southsoundtree said:
It seems BCs happen when internal stress overcomes internal strength.
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i characterize as massive internal competing forces overflowing their container, over ruling the constitution of the spar. Massive train force lunging forward vs. a full stop pushing back, giving split decision of BC of neither winning nor losing the fight. Usually more from full across Dutching/early close I think. Because a step on 1side to close offers the other side as potential path of relief. Slow fall can allow force to build to this too, rather than more flowing forward fall. Velocity gives squared increase in E=MCsquared, carrying the tree more cleanly, deftly .

evo said:
My point is stick to the rules until you know different. Look at the fibers, look at the tapered hinges.
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(y)Most best is L-earning to forensically read own stumps/hinges well enough to reverse engineer to consistent model of what is going on . What made what part go well or not, well enough to l-earn a ton from even other folk's hinges. i even remembering old hinges to gain unharvested lessons and confirmations as figured things out. Then even carrying same examination aloft to work more horizontally in tree, to then carry those lessons even more confidently back down to the base of the tree, as Dent showed them originally.
 
So today I cut an open faced notch that was 70% deep. It was on a small 40 ft tall codom and I felled it against the lean so the brush would be facing up. After felling the ‘front’ stem, we used a Maasdam to offset the lean and eventually pull the second part on over.

I thought to myself: “I should take a picture and post it on that 1/3 rule thread!” Instead, I kept working. The hinge was slightly less than 80% and 1 in. thick. The back cut was only 2 in. deep. With a few clicks on the puller, it layed exactly where it was aimed.

The original post was questioning the dated 1/3 rule. Using solid technique and modern ‘rules of thumb’ has served me well. Today reminded me there are many ‘updates’ needed across the industry. I’m thankful for posts like this that encourage readers to seek out the ‘updates.’
 
Mark Chisholm, very intrigued with the cylinder diagram. Are there any numbers to quantify the stresses, as caused by dried inner wood shrinkage? This would allow the effect to be combined/superimposed to the simpler calculations of geometry, weight, lean etc causing stresses.



I think it would be an excellent idea to add the knowledge you alluded to to the current discussion. I think the whole point is there's a vacuum waiting for this knowledge to be published. Positive contribution for everybody's benefit. :)
 
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Somewhere else -cough sorry- where there's a parallel discussion I discussed the concept of the shear failure initiating, as some believe, at the plane between compression and tension fibers.

This might be shown to be false by viewing videos of barber chairs where the split initiates at the depth of the back cut (or maybe even above the bar i.e. not at the edge) - which is not the previously mentioned plane location because that plane is somewhere within the remaining "hinge" wood.

Can anyone find a video where it doesn't start to split at the edge of the back cut?
 
Bart_ said:
Somewhere else -cough sorry- where there's a parallel discussion I discussed the concept of the shear failure initiating, as some believe, at the plane between compression and tension fibers.

This might be shown to be false by viewing videos of barber chairs where the split initiates at the depth of the back cut (or maybe even above the bar i.e. not at the edge) - which is not the previously mentioned plane location because that plane is somewhere within the remaining "hinge" wood.

Can anyone find a video where it doesn't start to split at the edge of the back cut?
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NO... Don't even bother to look. using a standard back cut, BARBER CHAIR ALWAYS STARTS AT THE EDGE OF THE BACK CUT...

any suggestion that it starts in the plane between compression and tension is incorrect 100% of the time.
 
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If gravity is acting upon an asymmetrical tree, the plane of tension/compression will move as the back cut is being made.
 
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Very emphatic answer Daniel, I was really asking a polite leading question to foster classroom participation. :)

Upon further pondering, it occurred to me that from the world of mech eng the edge of the back cut is what is referred to as a stress riser. Ie there used to be a reasonable stress distribution prior to the back cut, across the log. As the back cut progresses the load is concentrated in lesser area and the portion of log above the back cut, that used to be in tension, goes to zero tension and abruptly transitions to maximum tension at the edge of the back cut. Abrupt rise in stress = likely shear failure location. Bending beam stress is highest at the surface (new "surface" is the edge of the back cut). If you transform the trunk lean torque to be about the post-barberchair high attachment point, it is conceptually putting the failure location in pull-apart tensile stress in the radial direction. To ruminate on, for the sake of understanding.
 
I have really been enjoying this thread. The bottom line is debate is an essential part of science moving forward. If we can’t debate and share ideas then there will be no advancements. This thread is a wealth of knowledge on tree felling and I have gleaned A LOT!

However, I was too impatient for @Daniel to answer his own question on this thread so I went to YouTube to find his answer. He answers his question about why a tree barber chairs in this video at 6:15.

Daniel Intentional Barber Chair

In my opinion Daniel your explanation in this video is nothing new that hasn’t already been discussed in this thread. But I do have a question for anyone still following it.

In my experience, I sometimes find that Spruce trees and Fir trees will have sap wood “peel away” as the hing closes before the tree hits the ground. Unfortunately, I don’t have a picture to share. Wouldn’t this suggest that at least on certain tree species the sap wood does hold stronger than heartwood? This peeling effect I’ve even seen pull hard enough to change the lay ever so slightly.
 
HigherGroundArborist said:
In my experience, I sometimes find that Spruce trees and Fir trees will have sap wood “peel away” as the hing closes before the tree hits the ground. Unfortunately, I don’t have a picture to share. Wouldn’t this suggest that at least on certain tree species the sap wood does hold stronger than heartwood? This peeling effect I’ve even seen pull hard enough to change the lay ever so slightly.
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Great question.. seems logical right.. I had it happen on a small cherry top maybe 20 years ago... back cut was a little high (2") and there was enough twist in the grain for the stringy fibers in the sapwood to tear past the notch, twisting with the grain right down under the notch into the trunk below. That top held on that side and by the time of separation had pulled hard to that side, well off the lay.... That was a real eye-opener..

I've learned so much from these kinds of mistakes.. first thing was to be more careful with the back cut. Keeping it level or within 1/2" especially of the tree has a twist in the grain. sometimes its the easy trees that we let our guard down on.. second thing was the awareness that this tendency is going to be species-dependent..

And yes, I've seen plenty of spruce and hemlock have fibers on the side of the hinge hang on with the potential to swing the fall off the lay... That's why we make wing cuts under the sides of the hinge. A wide open face also helps, because the tree gains enough momentum before the face closes that a little tug to the side from some little bit of fibers on the side of the tree isn't going to be able to pull it off the lay.. (see below video)


And I thought the exact same as you for a few years.. the fact that the sapwood fibers hold on and will tear down the trunk, rather than sever shows that the fibers in sapwood must be stronger (that is they are more resistant to failure) than the fibers in heartwood.. It's only logical, right?

Until it occurred to me that the sapwoods are the only ones that CAN rip down the trunk... because they have somewhere to go.. heartwood can't, not because of a differential in fiber strength, but for the only one reason.. POSITION... sapwood rips down the trunk because that's where it is, on the side of the trunk. It's so simple yet somehow it's easily misunderstood.... there's a lot of that simple misunderstanding of the many distinctions involved in cutting trees... The idea that a barber chair is caused by the same sheer force that splits large horizontal limbs is another example of a commonly held fallacy, as is the idea that its cutting speed to form the hinge, not hinge placement determined by the depth of the notch that creates the tendency for barber chair.

I appreciate your patience with the answer to the question on the effect of notch depth. I'm thinking about doing a video about it. Didn't want to keep you waiting on this one.

 
Cross post from the other side of the tracks. Warning: in the monotone voice of the teacher taking attendance in the movie Ferris Bueller's Day Off.

Bit of spare time. Found it.
edit - oops, that was the wrong one, though worth a watch for the basics. This was the video:
Nope. Third time's the charm:
 
did you watch the third one???

He suggests cutting the notch on front leaners only 1/6th diameter, the using a plunge cut... that's only necessary when there is so much front lean that the bar might get pinched just making the notch, which is the exception rather than the rule.. The plunge cut avoids the BC, but we are still nowhere nearer to answering the question as Terry doesn't address it....


SO....
HOW DOES A SHALLOW FACE INCREASE BARBER CHAIR POTENTIAL?

any other input????
 
Bart_ said:
Very emphatic answer Daniel, I was really asking a polite leading question to foster classroom participation. :)
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It's emphatic because it's true. I've been pulling trees with equipment for years and like to leave fat hinges, especially when the tree has side weight over the house etc.. So many times seen and I've seen and heard the tree starting to snap crackle and pop as it starts to barber chair. ANd beyond personal experience, there is just the common sense of understanding what is going on with the wood fibers. You don't need a lot of impressive vocabulary and a bunch of diagrams to know that the tree HAS TO SPLIT at the end of the back cut... Same for the effect of notch depth... you only need to see a shallow notch tree split out and BC once to understand the very real consequences of the shallow notch.

People that think otherwise must not have seen it...
 
At 63 I continue to be a clear fell faller in Australia (Native Harvest) and I think experienced enough to add to this thread. Most of my work is in steep rocky terrain felling the split prone “mountain” and “alpine ash” (E. regnans and Delegatensis). The trees are all 50 – 60m tall and the “alpine ash” develops heavy leans downhill and into the side gullies. As a result every tree has the potential to “barber’s chair”.

I pour just under 20L of bar oil through my 661each week with no bucking or limbing. Eight thousand ton of wood on trucks is a big month whilst I am the only hand faller on the crew it is a credit to the logging team to snig, bark, process and load the trucks. On a country or world stage I don’t consider myself any better than any other production faller. Arboriculture stands to benefit from the production logging rather than reinvent the lessons learnt in blood. It is with some bemusement I observe the devising of odd felling methods and “trick shots” when the focus ought to be a pursuit of core skills and safety.

The above is not meant to be a “pissing” contest however I would be the first to want to know the background of a person making comment so it is only fair I give that. I also have a major in biomechanics and have applied those principles to my almost completed book.

I find that practitioners can be lost in technical explanations that at times smack of intellectual snobbery. For this reason I prefer to speak to practitioners in lay talk that we can all understand. I propose to discuss only the accepted general principles of tree falling relating to the thread. Extremes and variations will invariably produce difference and argument.

I would like to discuss three items,

Why the 1/3 scarf? The primary purpose of the felling cuts is to maximize the directional control of the tree. The accepted scarf is aimed between ¼ and 1/3 in depth. At 1/3 depth the front of the hinge is approximately 95% of the diameter of the tree. As a result the directional control is almost maximized when we consider that the hinge is behind this and thus wider.

Strength of the fibers across the hinge This varies between species, their age and across the hinge itself. In our Australian hardwoods the strongest fibers to hold and control the direction of fall are either side of the hinge. These two extremities must remain intact. For this reason the recent and novel introduction of “wing cuts” here by arborists has increased the loss of directional control and mirth from commercial hardwood fallers.

The customizing of the arborist tree felling training likely has poor “Google” influence as some key elements are in conflict with long standing cornerstones for commercial fallers. We are very public on forums now and ought to consider how we influence folk and our displays of professionalism. Many soft wood trees retain reasonable hinge quality across its length. Applying one rule is doomed for reasonable conflict.

I don’t recall where in this thread but there was reference to the tension of the outside fibers of the trunk. This is strongly evident in the straight (vertical) E. regnans prior to falling. When placing the first cut of the scarf it releases the tension on that side allowing the top of the tree to tip gently away from the cut. As the 60m top moves away it bends and pulls further. The head pulling away from the cut exaggerates the release of tension. This clearly demonstrates the dangers of overcutting hinges or demanding “wing cuts” in hardwood trees. Control is reduced.

What causes “Barber’s Chair”?

The primary cause of “Barbers chair” is the uncut wood to the rear of the hinge. Leaving a “strong hinge” despite a “back release” can initiate a “Barbers chair”.

The natural tendency of the timber to split gives a predisposition for the trunk to split up and down the trunk. The balance between the strength of hinge and tendency of the trunk to split can result in either the hinge breaking or a split occurring up the trunk.

Height of the tree (leverage) and the natural lean of the tree. The faller needs to make a decision of the method used to fell the tree that ensures the wood behind the hinge is cut before it encourages the trunk to split.

Step. The greater the lean the more it is beneficial to lift up the back cut. Mark correctly discusses the concept of the hinge bending. If you consider the hinge to be a board. By clamping a board in two positions close together and then forcing the board to bend between them the length of that bend and thickness across the board resists breaking.

Great examples are shown in this thread and others in the break of the hinges. Where you identify very little step of the back cut, the rear of the hinge displays the typical tall “pulled wood” whilst the front margin of the hinge displays the classic crushed broken fibers under compression.

Raising the back cut up higher is similar to separating the two clamps on the figurative board further apart. Now the bending occurs over a longer length for the same width of board (hinge). It will now bend and break the hinge with little or no pulled wood to the rear of hinge. This demonstrates a reduction of exposure to “Barbers chair”.

Scarf. It is preferred to install a scarf with the standard depth however from the above points if the critical wood is severed behind the hinge and the step height of the back cut is sufficient “Barbers chair” will not occur. The argued depth of scarf is not so much a “smoking gun” for “Barbers chair” that some declare.

There will be times with very heavy leaners where placing a 1/3 scarf is very hazardous or not possible because the tree continues tip forward and “sit” onto the saw in the scarf. If the scarf is about 1/3 depth and its length is about 95% this has little value for the direction of fall for a heavy leaning hardwood tree when back released. When the tree is released it falls where it is leaning and the hinge competing with its desired direction with gravity will fail.

Over cutting either of the two scarf cuts also encourages “Barbers chair”. As the overcut closes the hinge thickness is artificially increased. The uncut hinge wood to the rear must pull vertically up to break. The momentum of the tree tipping forward can either break the hinge or initiate the trunk to split up. In our hardwoods this outcome is likely. Softwoods and smaller trees can react differently.

Sorry none of the pictures wanted to load.

Regards

Graeme McMahon
 
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