# falling 101



## TheKid (Dec 13, 2007)

Am I correct in stating that a downsloping backcut is improper procedure when felling large trees (10"dbh and above)?


----------



## Canyonbc (Dec 13, 2007)

Ya i would say so.


----------



## joesawer (Dec 13, 2007)

TheKid said:


> Am I correct in stating that a downsloping backcut is improper procedure when felling large trees (10"dbh and above)?



Yep. That sloping back cut is some ignorant, amuter idea to prevent kick back or set back or something. They usually are not sure what they are trying to prevent or how it is actually supposed to prevent it.


----------



## turnkey4099 (Dec 13, 2007)

joesawer said:


> Yep. That sloping back cut is some ignorant, amuter idea to prevent kick back or set back or something. They usually are not sure what they are trying to prevent or how it is actually supposed to prevent it.



Back when I was young and stupid (young no longer applies) I thought a sloping back cut would give a wedge more effect. Then I got edumacated.

Harry K


----------



## Husky137 (Dec 13, 2007)

A sloping backcut on any tree is pointless. It also makes it more difficult to wedge the tree in the desired direction after the tree sits down on your bar.


----------



## teamtree (Dec 13, 2007)

not to mention making it more likely for the hinge wood to break and the tree fall backwards


----------



## diltree (Dec 13, 2007)

You also loose your ability to use a hinge to manipulate the direction of the fell.


----------



## (WLL) (Dec 13, 2007)

it think is makes a simple procedure more difficult but it has the same result. i am interested in what others have to say about this practice. i seldom see this method being used in commercial tree maintenance,and its most often homeowners i c doing it.for now its hard for me to say its wrong because just the other day i saw a near genius engineer doing it, i should of asked him why. maybe just more brains than common sense. i think this is a great post,and i agree it is poor practice for most trees, but i wonder if it has its place in arborculture.


----------



## Canyonbc (Dec 13, 2007)

My experince with SOME not All engineer is yes they are smart and normally very good at there specific field...but outside of that they are not. 

They think they are perfect and cant do wrong...can never seem to give one advice. 

I removed 3 Cottonwoods for a civil egineer last summer...man all day was he on my case about this and that...the first half an hour of his #####ing...i kind of lied told him my insurance doesnt allow homeowners do communicate with myself or workers for safety reasons. 

He did...but man o man was he a pain. 

Not saying all engineers are like this...i am making a generalization. 

Sorry not trying to change thread. 

Cut a 1/3 face level from the back...use a wedge...rope for extra security with a constant pull.


----------



## 2FatGuys (Dec 13, 2007)

Engineers can help to understand things though at times. I have used a sloping backcut a few times, for specific reasons. The few times were when it was going to take a lot of wedge to lift the tree over the face cut and would be difficult to get to the wedge location due to obstacles.

There are times when it may be easier to "push" the tree over with wedges than it is to "lift" it. I can get into the math side of it if necessary, but to simplify it, think of it this way: is it easier to make a standing log fall over by lifting from the bottom or pushing from the side?

However, the ONLY time this works is if the sloped back cut is beyond a 45 degree angle. It is VERY difficult to get the angled back cut to align correctly with the material removed from the face, hence the warnings about breaking the hinge. I have used this on a few VERY heavy trees when canopy weight and lean were against me. It helps the wedges to drive in, rather than just bounce under the excessive loading. It makes for an ugly stump to clean up. It isn't easy. And it has to be precise. Anything short of perfect looks like an amature job.

I KNOW I'll get some hefty rebuttal on this. Bring it on... But I know when and where it has helped. Not many times.. but enough to not discount the process.


----------



## (WLL) (Dec 13, 2007)

fecrousejr said:


> Engineers can help to understand things though at times. I have used a sloping backcut a few times, for specific reasons. The few times were when it was going to take a lot of wedge to lift the tree over the face cut and would be difficult to get to the wedge location due to obstacles. _*(wll) if you cant get to the wadge than how ya gonna cut the tree?*_
> There are times when it may be easier to "push" the tree over with wedges than it is to "lift" it. I can get into the math side of it if necessary, but to simplify it, think of it this way: is it easier to make a standing log fall over by lifting from the bottom or pushing from the side?
> 
> However, the ONLY time this works is if the sloped back cut is beyond a 45 degree angle. It is VERY difficult to get the angled back cut to align correctly with the material removed from the face, hence the warnings about breaking the hinge. I have used this on a few VERY heavy trees when canopy weight and lean were against me. It helps the wedges to drive in, rather than just bounce under the excessive loading. It makes for an ugly stump to clean up. It isn't easy. And it has to be precise. Anything short of perfect looks like an amature job. _*(wll) if the tree has a back lean over center than driving the wedge will put the back lean weight on the hinge(scarry)just put a rope high in the tree! a few mm of wedge will give you a few+ inches up top but should only be used on a good strait tree/spar. just put a rope on it. i use the wedge to keep the tree from rocking back*_
> I KNOW I'll get some hefty rebuttal on this. Bring it on... But I know when and where it has helped. Not many times.. but enough to not discount the process.


 look up i wrote after where it says (wll) i hope u can understand.


----------



## joesawer (Dec 13, 2007)

fecrousejr said:


> Engineers can help to understand things though at times. I have used a sloping backcut a few times, for specific reasons. The few times were when it was going to take a lot of wedge to lift the tree over the face cut and would be difficult to get to the wedge location due to obstacles.
> 
> There are times when it may be easier to "push" the tree over with wedges than it is to "lift" it. I can get into the math side of it if necessary, but to simplify it, think of it this way: is it easier to make a standing log fall over by lifting from the bottom or pushing from the side?
> 
> ...





The problem with angling your back cut over 45 degrees and then driving a wedge to push the tree over on one that is to heavy to lift is that the wood will split long before it will compress much. So a wedge can lift way more than it can push. A wedge will lift way more than most people will ever get the opportunity to use. To get the most out of it requires a steel wedge with shims and good technique. These can provide enough lift to make the wood in the stump buckle from compression. To help avoid this use more wedges to spread the pressure out over more area. 
If a plastic wedge is just bouncing when you hit it try adding more wedges, finer taper wedge, steel wedge (not the wood splitting type), cutting a wider kerf to help the wedge start moving. If you are doing tree work you are probably in over your head at this point and need to put a line in it and pull it over.


----------



## (WLL) (Dec 13, 2007)

*geee wizzz*

gee wizz this thred's going to chips,and im all outa wedges. so lets get back to the poor practice of why you should or should not use sloped back cuts.


----------



## (WLL) (Dec 13, 2007)

joesawer said:


> The problem with angling your back cut over 45 degrees and then driving a wedge to push the tree over on one that is to heavy to lift is that the wood will split long before it will compress much. So a wedge can lift way more than it can push. A wedge will lift way more than most people will ever get the opportunity to use. To get the most out of it requires a steel wedge with shims and good technique. These can provide enough lift to make the wood in the stump buckle from compression. To help avoid this use more wedges to spread the pressure out over more area.
> If a plastic wedge is just bouncing when you hit it try adding more wedges, finer taper wedge, steel wedge (not the wood splitting type), cutting a wider kerf to help the wedge start moving. If you are doing tree work you are probably in over your head at this point and need to put a line in it and pull it over.


O so your saying because a wedge can lift far more than it can push if you use a strong angle back cut you are now pushing with the lifting power of the wedge. does anyone understand this? i think i do.


----------



## joesawer (Dec 13, 2007)

(WLL) said:


> O so your saying because a wedge can lift far more than it can push if you use a strong angle back cut you are now pushing with the lifting power of the wedge. does anyone understand this? i think i do.



I am saying that if you drive a wedge into an angled back cut, a piece will split off the stump and you will loose all lift or push long before you will run out of lift from placing wedges in a proper back cut.


----------



## TheKid (Dec 13, 2007)

thanks all for helping settle a bet. thanks wll for trying to stay on target. I would love to hear more from others on this practice of the sloping backcut, which I've always been taught is wrong.


----------



## 2FatGuys (Dec 13, 2007)

Guys.. I'm not arguing, belittling or debating. If you re-read my post, I explain that there are very few times that I've used this technique. I would prefer to never use it also, but as I explained, there have been a few... VERY few.. times when it has been used for different reasons. I was in no way advocating that sloped cuts become routine. I was only trying to show that sometimes situations dictate that we do something out of the ordinary.

For the record, maybe due to significant review prior to cutting, I have never had the wedge split the stump prior to levering the tree to where I wanted it to go.


----------



## (WLL) (Dec 13, 2007)

(WLL) said:


> O so your saying because a wedge can lift far more than it can push if you use a strong angle back cut you are now pushing with the lifting power of the wedge. does anyone understand this? i think i do.


i may be on to something here. can some others that understand what i said above add or :help:? with a strong angle back cut you are now pushing the tree with the wedge. with a traditional horizontal back cut you are lifting the tree with the wedge. common:monkey:sense tells me that is correct


----------



## Burvol (Dec 13, 2007)

TheKid said:


> Am I correct in stating that a downsloping backcut is improper procedure when felling large trees (10"dbh and above)?



You're from Oregon? Never attempt retarted :censored:


----------



## Mitchell (Dec 13, 2007)

*sloping back*

Nevr seen anyone do that who falls for a paycheck. Not saying it might not have merrit; however I doubt it. On a large tree it would be a pain to line up the back cut. It would be a lot of extra cutting [away from the grain which would be slower going] when you might want the extra speed to nip a corner to pull it back into leed.


----------



## czar800 (Dec 14, 2007)

i may be on to something here. can some others that understand what i said above add or ? with a strong angle back cut you are now pushing the tree with the wedge. with a traditional horizontal back cut you are lifting the tree with the wedge. commonsense tells me that is correct

I am with you on that WLL, I have a feeling that just maybe my other post in the pic. forum got this started.. I pulled this tree with a over 14,000lb farm tractor. Yes it would have been harder to wedge in a desired direction.

I am new a so far i love this sit 

View attachment 61069


View attachment 61068


----------



## (WLL) (Dec 14, 2007)

czar800 said:


> i may be on to something here. can some others that understand what i said above add or ? with a strong angle back cut you are now pushing the tree with the wedge. with a traditional horizontal back cut you are lifting the tree with the wedge. commonsense tells me that is correct
> 
> I am with you on that WLL, I have a feeling that just maybe my other post in the pic. forum got this started.. I pulled this tree with a over 14,000lb farm tractor. Yes it would have been harder to wedge in a desired direction.
> 
> ...


 nice pic's looks like ya cut all the hing off too. good thing the tree wanted to go the same way you hoped she go:greenchainsaw:


----------



## czar800 (Dec 14, 2007)

WLL where at in pa are you from? I live in Ellwood City about 40 miles north of Pittsburgh.


----------



## (WLL) (Dec 14, 2007)

czar800 said:


> WLL where at in pa are you from? I live in Ellwood City about 40 miles north of Pittsburgh.


 bucks county


----------



## smokechase II (Dec 14, 2007)

*pushing*

Pushing a tree with an angled back-cut will be prone to breaking the hinge and ineffective due to its location. That is a very short lever arm and my experience is simply; lifting is effective.

With dead, (lightweight), smaller trees I like to cut as low as possible so I can stop cutting with the correct hinge then just push it over with my body.
My point here is if you're dropping a tree where the angled back-cut would work. Skip it and do the least amount of work.

{On most trees, cutting with a significant angle takes awhile. A cut angled at 45 degrees takes longer not just because of the amount of wood to be cut but at that angle the saw cuts poorly. Great chips at 0 degrees - with the grain, good chips cross cutting at 90 degrees, poor chips at 45.}

Possibly because of how ineffective an angled back-cut is in bigger timber, I've never heard a single experienced sawyer suggest that in the Pacific NW. Every single angled back-cut stump is peed on immediately and openly regarded with disdain.

**********************

Exceptions can exist. Let's say a cutter finds a tree that is already hung up. Of course, he found it this way. It wasn't his fault.
Cut a steep Humboldt and angle the back-cut down to match the angle of the Humboldt. The objective here is to either walk the tree down or have the jump help kick it free. 
That sort of angled back-cut, generally without the face - just two angled cuts meeting, has been referred to as a Texas B_____ cut here.
Caution on toes smashed, bars pinched and tops/limbs coming down to kill you.


----------



## BC WetCoast (Dec 15, 2007)

smokechase II said:


> P
> 
> Possibly because of how ineffective an angled back-cut is in bigger timber, I've never heard a single experienced sawyer suggest that in the Pacific NW. Every single angled back-cut stump is peed on immediately and openly regarded with disdain.
> 
> ...


----------



## (WLL) (Dec 15, 2007)

BC WetCoast said:


> smokechase II said:
> 
> 
> > P
> ...


----------



## moray (Dec 20, 2007)

fecrousejr said:


> There are times when it may be easier to "push" the tree over with wedges than it is to "lift" it. I can get into the math side of it if necessary, but to simplify it, think of it this way: is it easier to make a standing log fall over by lifting from the bottom or pushing from the side?



It seems most of the comments here had to do with the relative weakness of the stump when you try to wedge a steeply angled back cut. Can't argue with that. But the math should be identical. In both the flat and angled back cut, the wedge operation does exactly the same thing: it causes the tree to rotate around the hinge as the kerf opens up. The angled wedge should have a slight mathematical advantage in this regard, as it is slightly farther from the hinge than in the flat case, and thus would have a bit more mechanical advantage.


----------



## ropensaddle (Dec 20, 2007)

I don't normally cut angled but remember doing a slight
angle on a couple of occasions, once to miss a nail I
did not see until face had been cut and another because
I hit something in face witch caused saw to cut crooked
and did not want to climb the hill back to the truck so
cut angled. As a practice no a standard notch is the
one I use.


----------



## Cedarkerf (Dec 20, 2007)

moray said:


> It seems most of the comments here had to do with the relative weakness of the stump when you try to wedge a steeply angled back cut. Can't argue with that. But the math should be identical. In both the flat and angled back cut, the wedge operation does exactly the same thing: it causes the tree to rotate around the hinge as the kerf opens up. The angled wedge should have a slight mathematical advantage in this regard, as it is slightly farther from the hinge than in the flat case, and thus would have a bit more mechanical advantage.


Not buying that. By lifting the back straight up your moveing the leverage of the top. The angle cut your trying partially to push the tree over at the bottom. Its all about leverage over a long distance. Not pushing on the bottom.


----------



## teamtree (Dec 20, 2007)

*not sure about the math.....*

but go out and experiment and you will see a big difference. I bought a few acres sometime ago and spent the winter experimenting with different cutting styles. The idea that the wedge in the angled back cut should offer the same advantage as a flat back cut does not fly with my experience. You get more lift on a flat back cut. On the angled backcut you get more pressure to the outside rather than up. Regardless, I know of no experienced fellers who use a sloping back cut. That should tell you something. I bet if you did about 10 trees (5 & 5) you would see a difference as well. I can't explain the math or the geometry but I know what works.


----------



## Unknown Cutter (Dec 20, 2007)

the guys that are using the angled backcut are probably not leaving any holdingwood. they cut strait through the hinge. 
maybe it does help reduce kickback if your standard practice is questionable to start with


----------



## moray (Dec 20, 2007)

Cedarkerf said:


> Not buying that. By *lifting the back straight up *your moveing the leverage of the top. The angle cut your trying partially to *push the tree over* at the bottom. Its all about leverage over a long distance. Not pushing on the bottom.





teamtree said:


> but go out and experiment and you will see a big difference. I bought a few acres sometime ago and spent the winter experimenting with different cutting styles. The idea that the wedge in the angled back cut should offer the same advantage as a flat back cut does not fly with my experience. You get more lift on a flat back cut. On the angled backcut you get more pressure to the outside rather than up. Regardless, I know of no experienced fellers who use a sloping back cut. *That should tell you something*. I bet if you did about 10 trees (5 & 5) you would see a difference as well. I can't explain the math or the geometry but I know what works.



I'm glad to see this discussion showing some energy!

Let's distinguish between the math and the practice. In practice, wedging an angled cut won't work as well as a flat cut because of the nature of the wood, not because of the math. The thin lip of the cut where the wedge goes in is weak. It can and will bend. In the flat cut, the wood can only crush, not bend. The extra stiffness of the wood means less work is wasted on deforming the wood--the wedge is more efficient. So I agree with all the posters who state the wedge works better in the flat cut. 

However, that does not mean the math is different. The trouble with visualizing the whole process using words like "lifting" or "pushing" is that they imply two different processes are at work. But are they? Think of the spoked wheel used to steer a sailboat. I can make the wheel turn clockwise by pusing down on a spoke on the right side, or I can push up on a spoke on the left side. Are those different?

In the same way, it doesn't matter if the wedge is "lifting" or "pushing;" what matters is the wedge, whereever you place it, is causing the tree to rotate around the hinge. The resistance of the hinge to bending is the force that opposes you, and some of the weight of the tree if it is leaning toward the wedge. The very same forces oppose you whether you are wedging a sloping or a flat back cut, and the wedge in both scenarios wins the day in the same way, forcing the hinge to bend by opening up the kerf.


----------



## TexasTreemonkey (Dec 20, 2007)

Its kinda off topic but how do you get the tree to jump away from the stump?


----------



## juststumps (Dec 20, 2007)

moray said:


> It seems most of the comments here had to do with the relative weakness of the stump when you try to wedge a steeply angled back cut. Can't argue with that. But the math should be identical. In both the flat and angled back cut, the wedge operation does exactly the same thing: it causes the tree to rotate around the hinge as the kerf opens up. The angled wedge should have a slight mathematical advantage in this regard, as it is slightly farther from the hinge than in the flat case, and thus would have a bit more mechanical advantage.




the math isn't identical.......

lets say you have a 12 inch deep back cut,, you pound a 1 inch wedge in there... you have a 1 to 12 ratio

lets go with the 45 % back cut... to get to the same place at 45 % where the hinge is ,, is 17 inches !!!!!! now your down to a 1 to 17 ratio

on a flat cut your driving a force into the stump straight down,, and lifting the far end of the tree over your hinge....

on the angeled cut,, the driving force is pushing against the thin wood at the start of your cut... (some one posted this could break out ) and pushing into your hinge... instead of lifting it over....

on something with that small of a back cut,, it might not really matter,,,, but on bigger stuff,, it might...


----------



## (WLL) (Dec 20, 2007)

TexasTreemonkey said:


> Its kinda off topic but how do you get the tree to jump away from the stump?


well he%# thats easy, just use a jump cut. i have never made a tree jump off its stump without the help of blk powder


----------



## techdave (Dec 20, 2007)

*Look AT Physics of angled backcut+fibre considerations*

Hi guys, after reading all of this, and thinking about it (disclaimer-no beers were consumed in the analysis of this technique, so my creativity may be impaired), here are my observations. I AINT CALLING YOU DUMB if you use this method, just pointing out some reasons that just cuz it works for you dont make it right either. If it works for you and you are experienced with sloped backcuts, so be it. 


Sloping baccuts probably should NOT be used for at least three reasons that dont require mechanical analysis:

The greater tendency of wood to split as it is wedged closer to parallel to the grain. Cant wedge firewood apart at right angles to grain, can at parallel to grain, at 45 degrees likelihood of splitting is MUCH more than at right angles like in anormal backcut. Besides the oft mentioned worry about splitting the stump side of the backcut off the tree, might have to worry about the fibres at the hinge since he backcut does meet the hingewood, by definition. Propagation of a split at the hinge could cause a barberchair.

The complications that a sloped backcut causes if nipping corners or a similar correction to the initial hinge is needed. Much harder to meet cuts evenly without going into the hinge wood you want to leave intact.

The fact that wood is easier to compress under load if struck or loaded parallel to the grain than if it is loaded at right angle to the grain. Hammer onto the side of a 2x4 and then repeat at end, see which compresses easier. We want movement of the wedge, and the work expended to do so to actually move the tree, not to go for deforming it in the area of the cuts.


AND there are a few reasons to scorn sloped backcuts that are revealed when a diagram is drawn to analyze the physics involved.

First off, lets get out of the way the only advantage a sloped cut has:
In THEORY the force generated by trhe wedge is acting over a longer lever arm than for a right angled AKA regular backcut. True enough, draw it out and you will see. But skilled fallers who need to use a short backcut and still get a wedge in will bore the backcut to accomodate the wedge. or cut the backcut first and then the facecuts. OR If a longer backcut is needed the face is not cut as far in towards the center of the tree. (Why a longer backcut?? Longer backcut means less movement of top of tree for each inch of opening of the backcut, but also means less effort to drive the wedge each inch, and less stress on the fibers where the wedge is working.) 

So much for Fiber, what about forces?

The typical analysis of these forces and moments is based on the assumptions of classical physics. A frictionless pivot, or one whose friction is equal for all orientations of force and moment applied to it. A pivot whose integrity wil not be compromised for the range of forces and momentrs acting on it. And forces applied steadily and held constantly.


The pivot in this case is the hingewood, a non-linear and inelastic band of uncut fibres in the middle of the tree, not fricionless. But the fact the hinge doesnt behave like the ideal probably does not make a sloping backcut anyworse than the regular right-angled one.

The question of pivot integrity is a different kettle of fish. In an angled backcut a big portion of the force generated by the wedge is trying to push the tree forwards, a shear force on the hingewood that does not exist AT ALL in regular backcut. Probably wont matter for many to most situations, but in some thin hinge situations could be catastrophic extra load causing abrupt hinge failure before tree commits!!!!


Forces applied are not steady, nor held constant, and there is some friction-generated force on both sides of the backcut as the wedge is driven. These are abrupt shock loads, for an instant much bigger than the amount of force that actually does useful work moving the tree through measureable distances . These probably do not cause more probs in the sloped, unless the tree/cut is such that its near barberchairing Using SHIMS would usually greatly reduce this frictional problem in most types of timber.


Looks like long story short , most of the resons for not using a sloped have to do with the nature of wood fibres and grain and the stump and bole. But in at least one way the charaacteristics of the forces and moments involved in a sloping backcut may be less effective or more dangerous than in a regular horizontla one.

Thanks, Dave.


----------



## smokechase II (Dec 21, 2007)

*Texas Tree Monkey*

One trick that can be used to get a tree to jump off the stump is to use a conventional undercut that is wide. 50 degrees or so.

On the flat place a flat rock or whatever is handy that takes up 1/3rd to 1/2 of this gap in the widest part of the face. Then don't leave too much hinge, but leave some. Don't be cutting all the way through as it goes.

You want that hinge to provide some resistance when the top of the face connects to the rock insert, but weak enough that it will pop. You want the face a bit wide to make sure that you get momentum working to make it pop. But if you go with a really wide face, I.e. open face 70-90 degrees, the Pop and jump is too late.

This jump effect helps firefighters constructing helispots or fire lines move tree butts away from those projects. Breakage isn't an issue.

If one limits themselves to Humboldt or true Open Face technique, you'll never get to do this distance jumping.

I need to mention that this jump technique is somewhat limited to trees with height and/or weight that make their descent powerful. Also dead or brittle wood doesn't provide the pop needed.

***************************

A Block Notch with adequate snipe may accomplish the same jump.


----------



## moray (Dec 21, 2007)

juststumps said:


> the math isn't identical.......
> 
> you have a 1 to 12 ratio ...
> 
> ...



I think we are saying the same thing...almost. The "bit more mechanical advantage" that I alluded to you have shown precisely for the 45 degree case. When I say the math is the same, I mean the formula is the same, and nowhere does the formula include any reference to the orientation of the wedge or whether the back cut is flat or otherwise. I am trying to dispel any notion that wedging a flat cut has some sort of _mathematical _advantage over a sloped cut. When you figure the math, you and I both conclude there is more mechanical advantage in using the sloped cut, not the other way around. If you do a more complete anaysis that includes the properties of the wood (such as elasticity of end-grain vs face-grain, and the friction of each type of grain against the wedge, and the ultimate strength of the wood in both orientations), then things can get complicated. But the wedge doesn't know and doesn't care if it is "lifting" the tree or "pushing" it over.


----------



## teamtree (Dec 21, 2007)

I am not sure who is saying what but for those of you who think the math works out the same on a sloping back cut as a flat back cut when the wedge is inserted you are wrong. If you think of the tree as a bunch of pencils in a circle the example makes sense as you are applying a mostly up lifting pressure in a flat back cut. In a sloping cut you are applying pressure side to side and little to up lift. So the math, would come out more direct up lift with a 90 degree back cut than say a 45 degree. Simple math. 

At any rate, you are a fool if you think the sloping back cut is an appropriate procedure.


----------



## teamtree (Dec 21, 2007)

moray said:


> I think we are saying the same thing...almost. The "bit more mechanical advantage" that I alluded to you have shown precisely for the 45 degree case. When I say the math is the same, I mean the formula is the same, and nowhere does the formula include any reference to the orientation of the wedge or whether the back cut is flat or otherwise. I am trying to dispel any notion that wedging a flat cut has some sort of _mathematical _advantage over a sloped cut. When you figure the math, you and I both conclude there is more mechanical advantage in using the sloped cut, not the other way around. If you do a more complete anaysis that includes the properties of the wood (such as elasticity of end-grain vs face-grain, and the friction of each type of grain against the wedge, and the ultimate strength of the wood in both orientations), then things can get complicated. But the wedge doesn't know and doesn't care if it is "lifting" the tree or "pushing" it over.





bull####....you is a fool


----------



## GASoline71 (Dec 21, 2007)

moray said:


> I think we are saying the same thing...almost. The "bit more mechanical advantage" that I alluded to you have shown precisely for the 45 degree case. When I say the math is the same, I mean the formula is the same, and nowhere does the formula include any reference to the orientation of the wedge or whether the back cut is flat or otherwise. I am trying to dispel any notion that wedging a flat cut has some sort of _mathematical _advantage over a sloped cut. When you figure the math, you and I both conclude there is more mechanical advantage in using the sloped cut, not the other way around. If you do a more complete anaysis that includes the properties of the wood (such as elasticity of end-grain vs face-grain, and the friction of each type of grain against the wedge, and the ultimate strength of the wood in both orientations), then things can get complicated. But the wedge doesn't know and doesn't care if it is "lifting" the tree or "pushing" it over.



When "engineers" become fallers...

However... you will notice when the wedge does some weird stuff to the hinge when driving it into a sloped backcut.

Good luck... your gonna need it...

Gary


----------



## Unknown Cutter (Dec 21, 2007)

i have a question about sloped backcut for you math guys
it seems to me that if the backcut is angled up to the notch it would be more effective than if the cut angled down?
i dont use this cut but the discussion got me to wondering


----------



## (WLL) (Dec 21, 2007)

Unknown Cutter said:


> i have a question about sloped backcut for you math guys
> it seems to me that if the backcut is angled up to the notch it would be more effective than if the cut angled down?
> i dont use this cut but the discussion got me to wondering


dont matter to me if the glass is half empty or half full, aslong as its booze


----------



## moray (Dec 21, 2007)

techdave said:


> ...The typical analysis of these forces and moments is based on the assumptions of classical physics. A frictionless pivot, or one whose friction is equal for all orientations of force and moment applied to it. A pivot whose integrity wil not be compromised for the range of forces and momentrs acting on it. And forces applied steadily and held constantly...



Terrific discussion, techdave! It's great to see some really thoughtful analysis instead of the loud posturing so common around here. I'm working to extend some of your remarks, but I keep finding serious errors in my thinking. In the meantime, I wanted to publicly applaud your high-quality post.


----------



## moray (Dec 21, 2007)

Unknown Cutter said:


> i have a question about sloped backcut for you math guys
> it seems to me that if the backcut is angled up to the notch it would be more effective than if the cut angled down?
> i dont use this cut but the discussion got me to wondering



Unknown Cutter, if by effective you mean effective at pushing the tree over, then _mathematically _the angle of the back cut per se isn't an issue. But as others have pointed out, the greater the distance from the backcut opening to the hinge, the more effective the wedge, and that distance is greater the greater the angle of the backcut (for a cylindrical tree). But there are complicated practical issues for real trees, and techdave has done a great job at laying out a bunch of them.


----------



## TexasTreemonkey (Dec 21, 2007)

Lets just take a vote. I for one believe if there is not a foriegn obstacle (a fence) behind the stump and you can get a straight shot dont do an angled cut. period. 1 vote for straight.


----------



## juststumps (Dec 21, 2007)

moray said:


> I think we are saying the same thing...almost. The "bit more mechanical advantage" that I alluded to you have shown precisely for the 45 degree case. When I say the math is the same, I mean the formula is the same, and nowhere does the formula include any reference to the orientation of the wedge or whether the back cut is flat or otherwise. I am trying to dispel any notion that wedging a flat cut has some sort of _mathematical _advantage over a sloped cut. When you figure the math, you and I both conclude there is more mechanical advantage in using the sloped cut, not the other way around. If you do a more complete anaysis that includes the properties of the wood (such as elasticity of end-grain vs face-grain, and the friction of each type of grain against the wedge, and the ultimate strength of the wood in both orientations), then things can get complicated. But the wedge doesn't know and doesn't care if it is "lifting" the tree or "pushing" it over.



we are not saying the same thing.....the only mechanical advantage you are getting is in driving the wedge.....driving a 1" wedge into a 17" cut is easier than driving a 1" wedge into a 12" cut...
you would have to use a 1.5" wedge in the longer cut,, to get the same amount of work,, and then there goes you advantage...

i don't conclude at all... 

you might be mixing the properties of a lever up with those of an inclined plane

the wedge doesn"t care... its the hinge that does...


----------



## juststumps (Dec 21, 2007)

Unknown Cutter said:


> i have a question about sloped backcut for you math guys
> it seems to me that if the backcut is angled up to the notch it would be more effective than if the cut angled down?
> i dont use this cut but the discussion got me to wondering



only if you want to do it wrong,, and leave four foot tall stumps,, while having to fight the weight of your saw cutting up hill.....


----------



## juststumps (Dec 21, 2007)

moray said:


> Unknown Cutter, if by effective you mean effective at pushing the tree over, then _mathematically _the angle of the back cut per se isn't an issue. But as others have pointed out, the greater the distance from the backcut opening to the hinge, the more effective the wedge, and that distance is greater the greater the angle of the backcut (for a cylindrical tree). But there are complicated practical issues for real trees, and techdave has done a great job at laying out a bunch of them.



WRONG WRONG WRONG

you are really confusing the properties of levers and incline planes now...


----------



## techdave (Dec 22, 2007)

*Forces and backcuts...+thanks Moray*

HI moray, thanks for the compliment. Wish I could draw it and scan it!

Hi you all, the wedging creates forces acting on the stump and bole sides of the backcut. It also creates a moment aka torque on the stump and bole sides of the backcut.

The moment created is simply the force pushing apart the two sides of the backcut, times the distance from the place that force is applied to the hinge.

Orientation doesnt matter, as someone pointed out with their steering wheel analysis.

But FORCE, that is another matter. In a conventional (flat) backcut the forces generated as the wedge goes in are ONE a bigger one trying to move the two sides of the backcut apart. this is the useful effect we are movign the tip of the tree with to get it to go over in the desired direction. 

--- and TWO a lesser force from friction trying to push the stump over forwards, and by pushing the bottom of the bole forwrds cause rotation of the tree backwards. BUT neither of these things happen in a typcial cut, as the stump to be is too firmly rooted to rotate under the axe or hammer blows. And if the base dont move, and the hinge dont fail the only movement of the bole will be to roatate as the wedging TORQUE is trying to do. 

(IF IF IF the hinge were to suddenly fail during wedging the butt of the bole might mvoe forwards and cause the treeto fall backwards. this is similar to the effect people can get if they push too low on the tree with a loader or dozer.)

Back to force ONE above, if you diagram it out you will see the force from the wedge that is trying to open the sloped backcut has a large component pusing forwards on the bole of the tree trying to shear the hinge and move the bole off the stump. Possibly before the tree has committed to going the pro0per direction~!

BAsically as far as force and moment go, the angled backcut creates a greater rotational moment trying to tip the tree (acting on what could be a MUCH weaker aspect of the wood than in a conventional backcut), AND a MUCH higher shear force on the hinge, equal to the force pushing forwards on the base of the bole.

ALL of this, still dont see any good reason to slope backcut, and many reasons not to slope it.

All of this to reanalyze a cut most all of us agree is not a good idea!! DOH

ps to jump a tree off the stump, anything that breaks the hinge while the tree has got some of its rotation as forward velocity will cause the tree to jump forwards. 

If the hinge breaks to late, the center of mass of the tree is moving almost straight down, aka just before the tree hits the ground the hinge breaks.

A dutchman can be used intentionally for this purpose. A steeply sloped STOPE can help get the butt down on the ground quickly if the hinge has been broken somewhat early.


----------



## teamtree (Dec 22, 2007)

Well I apologize for my comments not having a scientific tone but I do have experience with both types of back cuts and to state it correctly, in my opinion, the sloping back cut does not provide an advantage in getting the tree to fall. I did not take notes of my experiements and maybe it was just luck. I know what works well and I have never had an experienced sawyer tell me to use a sloping back cut. I suppose if you are cutting some trees on a river bank or steep incline you may be able to use one. For that matter, you could use one on any tree. It is your choice and you are free to do what you want. 

I really wish I didn't read this thread to begin with because I doubt if the people who want a scientific explanation are worth their salt with a saw. Here is an idea, go get a government grant to figure out the forces and what not but at the end of the day, I doubt if you get all of us guys using a flat back cut to switch to a sloping back cut. 

Merry Christmas


----------



## ropensaddle (Dec 22, 2007)

The standard or common notch and back cut,the lumbermans notch and back cut and slight variations in notch width is all I use and a flat backcut is laid into them after kerfing for reference.


----------



## TheKid (Dec 22, 2007)

wow, this post has gathered steam! great! where's clearance? I don't know if this has been discussed yet, but the reason I was told not to execute the sloping back cut was that (esp if you cut the hinge accidentally) you effectively create a ramp for the butt to slide down the stump inspiring it to fall OPPOSITE the face cut.


----------



## moray (Dec 22, 2007)

*another thought*



techdave said:


> ...
> But FORCE, that is another matter. In a conventional (flat) backcut the forces generated as the wedge goes in are ONE a bigger one trying to move the two sides of the backcut apart. this is the useful effect we are movign the tip of the tree with to get it to go over in the desired direction.
> 
> --- and TWO a lesser force from friction trying to push the stump over forwards, and by pushing the bottom of the bole forwrds cause rotation of the tree backwards. BUT neither of these things happen in a typcial cut, as the stump to be is too firmly rooted to rotate under the axe or hammer blows. And if the base dont move, and the hinge dont fail the only movement of the bole will be to roatate as the wedging TORQUE is trying to do.
> ...




TD, in trying to extend what you have so clearly presented, I began to realize how complicated this whole thing gets when you leave the simple world of classical physics and start thinking about all the possible ways real wood is going to screw up the simple equations.

You rightly mention the friction between the wedge and the two faces of the kerf. We should add to your enumeration of the assumptions of the classical anaysis the assumption of a frictionless wedge. The frictional force on a real wedge is actually going to be enormous given the tremendous weight of the tree normal to the wedge, and we are certainly going to have to account for it in a more complete analysis. 

In the ideal case of a frictionless wedge, the only forces between the tree and the wedge will act perpendicular to the wedge faces.



techdave said:


> --- and TWO a lesser force from friction trying to push the stump over forwards, and by pushing the bottom of the bole forwrds cause rotation of the tree backwards. BUT neither of these things happen in a typcial cut, as the stump to be is too firmly rooted to rotate under the axe or hammer blows. And if the base dont move, and the hinge dont fail the only movement of the bole will be to roatate as the wedging TORQUE is trying to do.



The frictional forces of the real wedge act parallel to the wedge faces. For the upper face in the flat backcut the friction, as you drive in the wedge, acts to push the bole forward (as you noted). Isn't this just the "shear" force that everyone is so worried about that tends to break the hinge? Now it may be larger in a slanted backcut, but it seems it will be present in a flat backcut as well.

There seems to be universal agreement here that wedging a slanted backcut is much more likely to break the hinge, and maybe this is true, but I think someone needs to show that it is.

Here is a contrary thought that shows why I retain a bit of skepticism about this claim. Forget the wedge for a moment, but hang on to the hammer. Swing hard and hit the bole right above the backcut, trying to drive the bole off the stump. Now go up 30 feet and do the same swing striking directly above the first contact. The force vector is identical in both cases--the dreaded horizontal "shear" force that wants to break the hinge. But does anyone believe those two hammer blows are equally likely to be successful? It seems that distance from the hinge is a factor we must consider. 

This is an excellent problem, and there is certainly much more to it than has been discussed so far. I look forward to hearing what others have to say.


----------



## moray (Dec 24, 2007)

juststumps said:


> we are not saying the same thing.....the only mechanical advantage you are getting is in driving the wedge.....





juststumps said:


> ...driving a 1" wedge into a 17" cut is easier than driving a 1" wedge into a 12" cut...



With all due respect, juststumps, these two statements flatly contradict each other. 



juststumps said:


> WRONG WRONG WRONG
> you are really confusing the properties of levers and incline planes now...



And I don't think I am confusing a lever with an inclined plane; I am merely accounting for the fact that the scenario we are discussing includes *both *a lever and an inclined plane.

The inclined plane, of course, is the wedge.
The lever is the bole of the tree. The fulcrum for the lever is the hinge. We are applying force to the lever with the wedge, and the lever arm is the distance from the hinge to the contact area on the wedge. The load we are trying to move with the lever is the entire bole of the tree. The longer the lever arm, the more overall mechanical advantage for the entire system, which is why, as I have said, the slanted back cut has a theoretical advantage. Do you agree?


----------



## Mitchell (Dec 24, 2007)

*Dolmar*

Do not think it has been mentioned yet, but I seem to remember the Dolmar product brochure for 2007 has a guy cutting a slanted back cut? A European technique perhaps? 

I know the discussion is theoretical however, practically speaking A tree [if its cut right] would not be wedged off its hinge with out difficulty whatever the cut. 

Jumping trees= just cut the hinge as they are tipping.


----------



## clearance (Dec 24, 2007)

TheKid said:


> wow, this post has gathered steam! great! where's clearance?



Here I am. It is wrong, don't do it. The backcut should be level with the flat cut of the undercut, but slightly higher. Thats all, end of story.


----------



## moray (Dec 25, 2007)

techdave said:


> ... to jump a tree off the stump, anything that breaks the hinge while the tree has got some of its rotation as forward velocity will cause the tree to jump forwards.
> 
> If the hinge breaks to late, the center of mass of the tree is moving almost straight down, aka just before the tree hits the ground the hinge breaks...



I tried playing with the math involved with the jumping tree a couple of years ago, but when it got too hairy, I did an experiment with my camera instead. I stood up a wooden yardstick (the tree) on a flat deck railing and used a brick next to the base to keep the butt from moving away from the fall. Then I repeatedly let it fall, flat side down, toward the railing, snapping still shots at various stages of the fall. Results: the butt would first start moving away from the brick (jumping) when the yardstick was only about 15 degrees above horizontal. The typical jump distance was about 1 inch.


----------



## smokechase II (Dec 28, 2007)

*Wedging*

*Originally posted by juststumps 
...driving a 1" wedge into a 17" cut is easier than driving a 1" wedge into a 12" cut...*

_Then Moray's response: "With all due respect, juststumps, these two statements flatly contradict each other." _

**********************

Moray; I believe Juststumps is correct.
All other things being equal, face - hinge - wind - lean - wedges etc., the closer a wedge is to the hinge the harder it is to drive. 
If Juststumps is driving wedges at the very back center of the back-cut in both instances the longer distance is a longer lever.

What we have here is a failure to communicate.... err
What we have here is an incline plane lifting a lever.

The incline plane requires less force to drive if it is working with a longer lever.
The bottom of the butt log in the back-cut is a lever.

Besides the sloping back-cut being more work to make, if wedged its tendency is to push the tree off the stump (break the hinge) rather than pivot at the hinge.


----------



## smokechase II (Dec 28, 2007)

*lever arm drawing*

Jpeg for reference attached.


----------



## moray (Dec 28, 2007)

smokechase II said:


> *Originally posted by juststumps
> ...driving a 1" wedge into a 17" cut is easier than driving a 1" wedge into a 12" cut...*
> 
> _Then Moray's response: "With all due respect, juststumps, these two statements flatly contradict each other." _
> ...



He also said: ".....the only mechanical advantage you are getting is in driving the wedge....." The reason I called this a contradiction is there are *two *sources of mechanical advantage: the wedge itself, and the lever arm length. You and I seem to agree perfectly in every detail. By the way, smokechase II, nice diagram. Also, please pardon me for inserting notes in your quoted remarks (square brackets).

I measured the slope of one of my wedges--about 5.5 to 1. That's its MA, and it's favorable. The MA of the lever is very much against us. The center of mass of the tree might be 50 feet in the air, but the lever arm from wedge to hinge might be 18 inches. We are trying to move the long arm of the lever (50 feet) with the short arm (1.5 feet). That's a MA of 1:33. With a sloping back cut of 45 degrees, the short arm becomes about 2.1 feet. This would improve the MA to about 1:23, which, of course, is why it is easier to drive the wedge.

Loosely speaking, the hammer is another source of MA. Otherwise we would just leave it at home and push the wedge in with our hands.


----------



## windthrown (Dec 29, 2007)

Amusing thread. As a semi-retired (or is it retarded?) engineer, I think that a flat cut is more stable, and seems to hold a wedge better for falling. Wedges can and do weird things. They seem to float around more in angled back cuts, and vere sideways. They also tend to force the grain apart in an angled back cut, spliting the stump open more, which gives them less leverage.


----------

