Beginner Question On Hinge Formation When Felling, etc.

[Robert11]

Hi,

Great Forum. Thanks all, for the thoughts on which Stihl saw I should probably get.

First, let me admit that I have never felled any tree, irrespective of size.
But, as I've posted, am looking into getting a Stihl small chainsaw for clearing brush, etc. All very light stuff.

Am a retired Engineer, with some structural work, and have been thinking about the following a bit.
Am curious, and would be interested in anyone(s) explaining the following for me:

Let's say you have a perfectly symmetrical tree, no branches, standing absolutely
straight up. A telephone pole analogy, perhaps.

O.K., the center of gravity (c.g.) obviously goes right thru the middle.

I have watched a zillion YouTube and other videos, and the all say, every single explanation, that the first
directional cut (wedge) should be made inward no more than about 25 % of the diameter.

That means, of course, that the c.g. is "still" behind what will become the hinge after a felling cut is made
from the back.

So, unless wedges are used, the natural tendency therefore would be for the the tree to tilt backwards, it seems to me.
Again, as the c.g. is toward the rear of the hinge (behind the hinge)
This doesn't sound so good.

What am I, obviously, missing ?
Whey shouldn't the first cut be made over 50% of the diameter, so the c.g. would tend to tilt
the tree forward, when the felling cut is made from the rear ?

Interesting to think about this, for me.

Any thoughts on ?

Bob

 

[JTM]

Well, I’m no expert but the center of gravity will not always be within the footprint of the stump. You’re felling a tree and not a perfectly centered telephone pole. If you make a such a deep undercut opposite the lean the tree will likely go over backwards and barber chair in the middle of making such a cut. The tree’s natural lean helps determine the direction of fall. Part of the reason for the shallow undercut is that is usually where the wood fibers are strongest. I hear there are some good good books on felling trees.

 

[ATH]

If you cut past the c.g. with the wedge, as soon as the back cut is deep enough to allow the tree to tip, it will.

That is often (but not always - especially in your telephone pole example) a problem because the tree will either barber chair, pull fibers out of the middle, it may start to fall with too thick of a hinge - which means it may not continue with enough momentum, the hinge may not be straight which will take the tree the wrong direction.

Additionally, I assume you have seen the recommendations for a hinge that is 90 degrees? That is so the hinge directs the tree all the way to the ground. That would be difficult (not impossible...just more work) to cut a 90 degree hinge past the center point of the tree.

Finally, a perfectly centered tree is rare, if non-existent. As JTM said, most have some lean and your best bet (especially as a beginner) is to fall with that lean. It is not difficult to use wedges. And remember, even if the c.g. is perfectly centered on the stump, there is a LOT of mass outside of that, so it doesn't take much to change the c.g. with a little tap of a wedge. Doing so, you have full control of the hinge size and shape, and when the tree starts to fall.

 

[old CB]

Bob, with an engineer's mind, has proposed a perfect pole scenario (like a utility pole). With just the face cut, you're right the c.g. is still centered in the pole. With no cut other than the face, you'll find that pole has no tendency to go anywhere. With a face cut and a back cut, as long as you've left a proper amount of holding wood (10% of the dia. is standard) that pole will still stand until wind or a wedge in the back cut convinces it to do otherwise.

When wrecking a tree (climb and remove the limbs on the way up, then drop the top out) it's surprisingly difficult to fell the remaining spar because the c.g. is centered. This on a conifer with a straight stem.

Get some experience with felling and you'll find the holding wood will keep a spar standing way past the point that you would expect it to.

Find a friend or a pro to help you get started, and soon it will all make sense. And Jeff Jepson's book, To Fell A Tree, is a very good primer, at reasonable cost.

 

[JTM]

Torque/leverage/angular moment - a puff of wind through to canopy will translate to a lot of force at the stump.

 

[BC WetCoast]

When I'm falling a stub (short stem with branches and top removed) I will make the undercut deep, often to the pith.

If you watch some of Reg Coates' videos, when he is blocking down conifers (often with 20' logs) he will make the undercut deep to ensure the log will tip with minimum effort on his part.

 

[Mustang71]

I've cut more than 50 percent on the first cut and when I made the back cut it pinches the saw because it tries to fall backwards. Now if it has a bit of lean and you cut in the direction of the lean it all goes much better. For a straight tree you will most likely need a wedge or rope on it to direct it to fall. I would start on smaller trees and get the hang of the notch and back cut. That way if you mess up you have a better chance of getting the tree down safely.

 

[Skeans]

A perfectly centered snag I’ll typically shoot for 65 to 75% of diameter so I’m not wedging as well as have a stuck no movement tree. A typical face the 1/4 of the way to me is to small you’re always fighting it with wedges, I’ll typically go a 1/3 to 1/2 on big fir and cedar, our alder we cut the face in till the top just slightly moves.

Sent from my iPhone using Tapatalk

 

[Marshy]

Welcome to the site @Robert11. Your thought process is correct when dealing with a near perfect cylinder and no lean. In the real world those trees are few and far between. As suggested, the book by Jeff Jepson - To Fell A Tree, is a good read for someone learning how to safely take a tree down for the first time. Another good read is from Douglas Dent - Professional Timber Falling but, it requires slightly more than a basic understanding of how to properly cut a tree. None the less, both are good in their own way.

Both books will teach you how to assess a trees weight and lean. Even if you have a perfectly straight tree, it's very unlikely the branches are perfectly distributed. The south side of the tree gets more sun to naturally the branches will be bigger, heavier, and grow out farther which has an affect on the CG. That's just the branches. You also look at the overall lean of the tree which there are two parts to. Some trees may have a sweeping belly in the center of the trunk but tip half is straight, or you could have a straight mid section but the top is leaning because nearby trees. All of those thing come into play when determining the trees natural fall direction. Once you can assess the natural direction you need to determine if you can use that to get the tree down or if you need to steer the tree slightly off from the natural lean. The book goes into detail on how to accomplish that.

In my opinion, the biggest risk for people cutting trees for the first time comes from the tree getting snagged into other trees and not making it to the ground. That can be a particularly dangerous situation if you do not know how to deal with it. Of course there are several other risks through the cutting process that are dangerous and are not to be ignored.

 

[Marine5068]

A perfectly centered snag I’ll typically shoot for 65 to 75% of diameter so I’m not wedging as well as have a stuck no movement tree. A typical face the 1/4 of the way to me is to small you’re always fighting it with wedges, I’ll typically go a 1/3 to 1/2 on big fir and cedar, our alder we cut the face in till the top just slightly moves.

Sent from my iPhone using Tapatalk

Wow. Those are some big mothers. I would think you'd need to be very experienced to fell trees that big.

 

[Marine5068]

Watch this video of an expert felling trees.
He's a fantastic teacher in my opinion.

 

[ropensaddle]

Wow. Those are some big mothers. I would think you'd need to be very experienced to fell trees that big.

The bigger they are the harder they fall

 

[Jackbnimble]

If you want the very best most accurate information, do NOT read this.

Once the fibers are cut out of the top of the wedge, the structure supporting the weight directly above it is compromised. Removing the wedge eliminates more potential support material and opens an area for the tree to fall over unhindered. Because the back-cut is made below the location of the top of the wedge cut, the unsupported fibers from the wedge crumble first, causing the upper portion of the tree to collapse in that direction.

 

[northmanlogging]

Perfect world...

In a perfect world 25% face will always sit back as soon as you cross cg, which will be long before overcoming fiber strength and the minimal effect of a shallow face.

Essentially use a wedge, and get it started as soon as there is room in the back cut. This counter acts the backwards gravity allowing the face to do its job

 

[CacaoBoy]

Because the back-cut is made below the location of the top of the wedge cut . . . .

A screenshot from that excellent video posted by Marine5068