Hinge Cutting Trees: Safety and Control 101
Before starting your own hinge cutting activity, please read the article below and watch the videos closely on the Hinge Cutting page while Jim explains the correct way to hinge cut trees safely and points out some of the possible hazards involved.
The See More Bucks team’s videos and articles involve the use of some potential life threatening activities such as the use of tractors and other farm equipment, chain saws, the felling of trees, use of certain agricultural chemicals and other potentially hazardous materials and activities. It is the responsibility of members to ensure that they are using appropriate safety measures and are trained to perform activities and use materials. Whitetail Ambush Secrets Inc. assumes no liability for any injuries, damages or loss of any kind that might arise from the use of information from our website or in any other venue.
HINGE CUTTING: SAFETY AND CONTROL.
February 10, 2016.
What is hinge cutting and how does it differ from notching and back cutting a tree? To start, let’s consider what it is we are doing when we do a hinge cut. Standard tree felling procedures involve making a notch cut and then a back cut (also called a felling cut), which ends near a hinge, resulting in the tree falling in the direction of the notch (it is actually the hinge that primarily controls THE direction of fall–the notch just creates a space for the tree trunk to fall through). When properly done by a professional, this can be accomplished with enough accuracy for the tree to drive a stake in the ground at the desired location.
When we do a hinge cut, we skip the notching part, and the hinge becomes not the wood between the notch and felling cut, but the opposite face of the tree. As with notch cutting, a good hinge cutter should be able to land the tree where he wants it (although accuracy suffers a bit).
This image from the OSHA website shows how to properly do a notch and felling cut.
Figure 1. Page on OSHA website showing how to do the notch and back cut when felling a tree. Methods for creating the notch vary, but the back cut is always done on a horizontal plane and the tree is never fully released but is stabilized by a hinge that is left remaining.
Notice that they say: “Important—cut flat along a horizontal plane.” They are not saying this for no good reason. A horizontal felling cut is one of the most important factors for maintaining safety and stability of the tree, and a flat horizontal cut is recommended in every professional training manual and video I have ever seen.
Every chainsaw company tells you how to fell a tree in their manual. We all know they do it for a reason. It covers their butts. They tell you how to properly cut a tree. If you don’t do it properly, that’s your problem, not theirs. They taught you how to do it right. Every company teaches to do a horizontal felling cut. Most chain saw owners pay no attention to the how-to section of the manual, and go out and start cutting in a way that seems intuitive to them. There is very little about tree felling that is obvious, it needs to be learned through study and practice.
Here are just a few links to how-to information from several chain saw companies—they all pretty much describe the same thing as OSHA does.
Husqvarna manual: http://www.jackssmallengines.com/pdf/chainsaw_cons.pdf
Stihl manual—they emphasize that the back cut should be “exactly horizontal:”
The biggest mistake I see novice hinge cutters doing is making an angled cut on the back cut. This, in combination with cutting too far through the tree, is the leading reason for break-offs. Intuitively, the cutter thinks that if he cuts at an angle the tree will be prevented from falling backwards. This belief arises from a fundamental lack of understanding of the fundamentals of how to cut a tree.
What is different about hinge cutting for habitat?
Hinge cutting consists of doing the back cut operation without a notch cut.
I borrowed from the OSHA image (Fig. 2) to show how I believe a hinge cut should be done to maintain the same stability and control that is provided by the horizontal felling cuts shown above. In this image, the hinge is the brown portion. In the above OSHA image (first image) it is the light brown area between the wedge and the back cut. When we hinge cut, instead of notching the tree and using an internal hinge between the notch and the back cut, we cut until the tree hinges on the opposite face. The mechanics of maintaining a stable condition are the same for either approach. In both standard cutting and hinge cutting, it is the hinge that controls the direction of fall of the tree. Most people think it is the notch that controls the fall of the tree. That is incorrect. The notch only exists to create a space for a tree that is going to be completely removed from the stump. You can prove this to yourself by notching and felling a few trees. Using an upright tree, if you create a hinge that is the same thickness all the way across, the tree will fall straight. If you make the hinge thicker on the right, the tree will tend to fall more to the left, and if you make it thicker on the left, it will tend to fall more to the right. It is the hinge that is the main controller of the direction of fall. However, other factors come into play, which we will discuss below.
Figure 2. A hinge cut tree is felled by doing a back-cut without creating a notch. In standard felling practice (figure 1) the hinge lies between the notch and the back-cut, whereas in hinge cutting the hinge is the face of the tree where the notch would normally be made.
An angle cut is much less stable than a horizontal cut.
To demonstrate how unstable an angle cut is, imagine that you have cut a tree all the way off flat, and another one all the way off with an angle. Now, cut a log from the fallen tree about 2 feet long and sit it on top of the stump. Think about the energy distribution in these two situations. In all cases (Fig. 3), the log shown on the left will just stay in place, because gravity is pulling it straight down and there is no angle to cause it to slide off. In contrast, the one on the right might stay on top but it might just slide off due to gravity. Now imagine you start pushing on each of these from any angle, front, back, sides, which one is more stable and least likely to slide off the stump? Even if I were to place a small nail on the stump at the lower right to help hold the slanted log in place (a surrogate for a remaining hinge), it will still have a tendency to twist and fall off. There is a tendency for that log to want to slide to the right, and if it has to pivot around the nail, it will do so. If picturing the log doesn’t help you, imagine placing a beer glass on top of these two stumps. What direction is the beer glass likely to go on the angled cut? That’s right, it is going to want to slide off to the right. If it is held in place by the little nail, and you push it to the side, it will rotate around the nail and fall off. If you do the same thing on the flat stump, it won’t fall of until you push it all the way to the edge–no pivot.
Now, when you put a whole tree on top of it and hinge angled vs. flat, the same tendency occurs, Even if there is lateral pressure from up the tree, the one that is flat cut is much less likely to twist or pivot around the hinge. You have much better control of the direction you take it. You can over-cut it and it still may remain standing with very little hinge. The worst that may happen is it will lean back or to the side and pinch your saw, which can easily be corrected with wedges. In contrast, the one on the right, if you over-cut it, is much more likely to push outward on the bark and cambium, and as it releases, pivot on the angled stump in one direction or the other, depending on the lean of the tree.
Figure 3. Example of setting a 2 foot long log on a stump made with a horizontal cut vs. one made with an angled cut. Angled cuts create an unstable situation. They lead to twisting and reduce the ability of the hinge cutter to control the direction of fall.
Figure 4. With a whole tree sitting on top of the stump, and a hinge attached, it is easy to see how gravity puts outward pressure on the hinge if the tree is released. With a flat cut, the tree above it has a flat platform to sit on, and remains stable. With an angled cut, the tree wants to slide off towards the hinge but because the hinge is holding it back, it will twist and break off much more often.
This is where the risk element comes in. You have a lot less control of an angle cut tree. You can probably do 10,000 angle cuts on little trees and all that will happen is you will lose more from twisting or bark disengagement, but when you do it with bigger trees (10-12 inches and larger) you run the risk of having less control of where the tree is going, and a much higher likelihood, when the crown hits the ground, of the hinge, which is already weakened by the lateral and outward forces, sending back an energy wave that will completely break the hinge. That’s a safety problem, but also an efficacy problem. You will get flat cuts to hang up on the stump much more reliably, creating great lateral cover, and potentially keeping the tree alive, a lot more often than you will with angled cuts.
Even if angle cutting was not less safe and stable, it would make no sense to do them just based on geometry alone. Fatigue is one of the most dangerous elements to cutting trees. You just get plain tired running a chain saw, and when you get tired, you are less alert and less likely to be able to move quickly when you need to. You have to spend a lot more time and effort to do angle cuts than you do accomplishing horizontal cuts. In the example below, we have a 4 inch tree with a flat cut and an angled cut at roughly 45 degrees. I would have to cut about 4.2 inches of wood with the angle cut for every 3 inches with the flat cut.
Figure 5. To fell this 6 inch tree, a 4.2 inch angle cut is needed vs. a 3 inch horizontal cut. That is an extra 10 feet of cutting for every 100 trees.
If I cut 100 trees of that size, I have to cut an additional 10 feet of wood. More time, more fuel, more muscle power, more noise, more sharpening of the saw, more wear and tear on the saw, more everything, and what do you get in return? Less control of the tree, and you are less safe. Tired at the end of the day? You can save a lot of time and muscle aches by cutting trees properly with a horizontal cut.
One exception to the rule. Some professionals will cut small trees at an angle, going all the way through with a very sharp saw, as they pass through the front of the tree the butt will slide forward and the rest of the tree will fall backwards. This is called “stump jumping” and is a means to clear many acres of trees and should be done only by professionals.
How far to cut—just enough.
The second most common mistake made by hinge cutters is to cut too far through the tree. Professionals always leave a piece of the tree attached to maintain control of the fall of the tree. A professional doing a notch and back cut to fell a tree has much more control than the hinge cutter does. The reason is he is using a hinge that is flat on both sides and is controlling the thickness of the hinge. In contrast, the “hinge” on a hinge cut tree is roughly a semi circle at the periphery of the tree, and comprising the hardest wood in the tree. This makes the direction of fall harder to control and the energy distribution at the hinge harder to interpret. Virtually all trees have regions of compression and regions of tension. If a tree is leaning to the right, the wood is being compressed in the direction of the lean and pulled tight, or put under tension on the other side of the tree. The main line of safety between the operator and the tree is to be sure that the tree remains attached to the trunk. If it is cut through so far that the tree releases on its own, breaking free, it is hard telling where the butt of the tree is going to go. For this reason, in many situations (but not all—see barber chair discussion below) we are inclined to err on the side of stopping the cut just before the tree releases.
If the tree is leaning back, for example, we are going to stop cutting before the tree begins to release. With practice, the operator will get a “feel” for when this is going to happen. It might be a slight movement of the tree, just a feeling through the hands on the chainsaw, or from experience with the species and the size and lean of the tree. Nonetheless, with practice, the cut can be stopped nearly every time before the release. With trees large enough to get a wedge in behind the saw, we will almost always place a wedge behind it in case we overshoot slightly. However, we want plenty of wood left after the cut—never exceeding 75% of the distance through the tree (on purpose).
At this point, we are either going to pull the tree down with a pole (I use one from Sherrill tree, Figure 6) use wedges, or a come-along to coax it over in the direction we want it to go.
Figure 6. Jameson fiberglass pole for pulling down trees comes in 6-8 foot length and accepts 4 foot extensions in increments. http://www.sherrilltree.com/Professional-Gear/Hollow-Fiberglass/6-Fiberglass-Pole-with-Sawhead
Besides the chain saw, the wedge is the number 1 tool in our arsenal. I carry 2-3 plastic wedges at all times when hinge cutting. A one inch plastic wedge will move the top of a 50 foot tree more than 8 feet. Most larger trees get a wedge unless they have severe lean that is gong to control the direction of fall naturally. Putting a wedge on the right side of the cut will move the tree to the left, and visa versa. There is no better tool for control of the tree than a wedge. These can be purchased almost anywhere that chainsaws are sold. But I usually just add them onto my periodic purchases at www.sherrilltree.com. This is a great site and catalog for boys who like their toys. Most trees can be tipped over by pulling or using wedges, but sometimes you may find yourself in a situation where you need to use a come-along. If you make a mistake and get your saw pinched you can pull the tree up by putting a chain or cable around it and attaching the come-along to another tree a safe distance away. A come-along can also be used to fell a tree against it’s lean when it is leaning to far for safe use of wedges. It is truly amazing how far you can take a tree against its lean with a good come-along. It is critically important to use one that can handle the load. Most come-alongs found in the average guys garage will not do the job if you are going top get into trees of 10 inches and larger (we do not recommend that you cut trees this size or larger until you get a few hundred hinge cut trees under your belt). The come-along is an essential tool that will save your butt and is well worth the expense. I use a two ton puller from Sherrill Tree (Figure 7).
Figure 7. Two-ton puller from Sherrill Tree. This is a much better choice than the lighter ones you will find in most hardware stores. http://www.sherrilltree.com/Professional-Gear/Static-Cabling/More-Power-Puller-926
It is essential to understand how the energy in a tree is distributed. Parts of the tree are under compression and parts are under tension. Think of the tension part as being like a fishing line that is being pulled tight. If it snaps, or is released, it will spring back. A leaning tree is under compression in the direction of the lean and under tension on the other side. When you cut through wood that is under tension, it may suddenly release. When it does so, it will send out wood perpendicular to the tension—that means back at the saw.
A barber chair occurs when there is pressure on the tree in the direction of fall, such as a lean, or pulling with a hook, or wedging, and when you cut to a certain point, the tree begins to split up the trunk, sending out a part of the trunk backwards and upwards from the stump, similar to the way the footstool on a barber chair goes up and out as the seat is pulled back. Professional loggers do everything in their power to avoid barber chairs, because they ruin the tree for timber and are dangerous, especially because the logger is usually cutting very close to the ground to leave as little as possible “on the stump.”
By definition, when you hinge cut a tree you are setting up conditions where a barber chair is likely to occur. You are doing things a professional logger cutting a tree would avoid at all costs. It is an unavoidable consequence of the fact that we are not doing a face cut, or notch, and we are cutting from the back of the tree, rather than bore cutting as a professional logger might do when faced with a leaning tree (the saw is bored into the tree near the hinge and the logger cuts backwards finally releasing the tree at the back side).
Here is an image showing the mechanics of how a barber chair works. In this case, the tree wants to fall to the left. A logger might notch it on the left side, would possibly do a bore cut to create a hinge, and then cut out towards the back of the tree to release it, preventing the tree from producing a barber chair. When we hinge cut, we do not put a notch on the tree because we want that part of the tree to stay attached, and serve as the vascular system to keep the upper part of the tree alive after it falls. Or, at the very least, even if the tree dies, to try to get it to hang up on the stump to create horizontal cover. As we start to cut (Figure 8), the leftward pressure from the top of the tree (top arrow) creates a force in the opposite direction at the bottom of the tree (arrows to the right). A straight-grained tree will then split at some point, sending a portion of the trunk back and up in a radius.
Figure 8. Barber chair forms when tree is leaning, and you begin to cut into it (1). At some point, tension is released and a split forms up the grain of the tree (2-3). As the tree falls, the split portion moves up and back, creating a dangerous situation for the unprepared operator.
Many folks who are doing habitat work try to diminish the likelihood of a split by cutting quickly into the tree or holding the tree upright by some means. Professional loggers will sometimes tie a chain or strap around the tree to prevent it from doing a barber chair. Perhaps some habitat guys do that but I have not seen any examples of it. Barber chairs are unavoidable in hinge cutting, and can actually aid the survival of a tree. Figure 9 is a diagram showing a tree with a barber chair, cut part way through and then coaxed over by pulling, wedges, or its own lean, and encouraged to fall as slowly as possible, and another tree without a barber chair (bottom). The key thing to notice here is that the top tree has a radius that acts like a spring for the bulk of the trunk to rest on. The energy is distributed over a wide area. There is a gradual curve that helps keep the vascular system of the tree open and free flowing. In the case of the bottom tree, which was cut through farther and not allowed to hinge, the cambium, or vascular part of the tree may be pinched, and the pressure of the butt of the tree is pushing right down on the hinge rather than resting on a spring. Having the tree split up a ways creating a flexible radius is the ideal outcome (Figure 9).
Figure 9. A barber chair can sometimes aid in the survival of the tree because a thinner, more flexible portion can bend as the tree falls (top), creating a long radius and preventing crushing of the vascular system of the tree. In contrast, a tree with a tight radius (bottom) may have constricted vascular flow.
Figure 10. A great outcome. There is a flexible hinge created by a slight barber chair effect that will help to keep the vasculature of the tree flowing.
Safety issues related to barber chairs.
If we are going to hinge cut, by definition, we are going to be breaking standard rules of safety from a professional loggers standpoint. Whereas habitat hinge cutting is growing in popularity, still, it is not so common that there is much written about the special, different safety requirement related to it. I am conveying my opinions about what the safety issues are and how they differ from standard practices, but as we progress over time I am sure both my approach and the way standardized approaches are written in the future will change.
One of the warnings you will hear is that it is more dangerous to cut up high on a tree. While that is true under normal circumstances, when you are hinge cutting, you are likely to produce a barber chair. If you do, the higher up it is, the lower the risk to you.
The reason is that the tree is going to kick back and up. The lower it is the more likely it is to contact your body. Here is an admittedly idealized drawing that shows the mechanics of what happens when a barber chair occurs (Figure 11)–caution, it will not happen like this every time, but this is what most barber chairs will do.
Figure 11. As a barber chair occurs, the butt of the tree traces a circle around the point up the tree where the split stopped. Thus, it goes up and back. The higher the cut, the less likely the operator will get hit by the barber chair.
The image shows a human standing 8 feet behind a tree that was hinged at 3 feet. As the barber chair progresses, it will move back and up, so that it misses the 6 foot man standing behind it. This is for demonstration purposes only, 8 feet is way to close to be behind a hinge cut tree of any size. As the tree begins to fall, I like to have a clear path at a 45-degree angle from my side of the tree and at least 20 feet distant. It is very important to not take your eyes off the tree.
Cutting a tree that is likely to barber chair is much safer at 5 feet above the ground than at 2 feet above the ground. You are exponentially reducing your chances of getting hit during the release when you cut higher. We need to cut lower sometimes because we want to create blocking cover, but the lower we cut, the greater the risk of getting hit by the hinge. This is the opposite of standard chainsaw safety, and it is true only because we are not doing standard cuts, we are doing something completely different, so the rules are changed.
When making high cuts, shoulder height and higher, it is necessary for the right handed operator to use the bottom of the chainsaw bar when you are to the right of the tree, and the top of the bar when you are to the left of the tree. This allows you to have your body as far as possible from the tree, and off to the side, while reducing contortion of the arms and wrists. Never let any part of your body get behind the tree while cutting.
When making low cuts, below the shoulders, the opposite is done. Lower cuts should be made with the top of the bar from the right side and the bottom of the bar from the left side. This allows you to keep your head back away from the tree. You can further add distance by only using as much of the bar as you need to. In other words, cut out towards the end of the bar, but well within the tip of the bar. Everything we do maximizes the distance of the head from the tree and provides a stable, comfortable posture and arm and hand position. If you feel you need to use the body of the saw, digging the bumper spikes in to get leverage to cut, you are either too tired or your chain needs to be sharpened. A good, sharp saw should easily be able to chew its way through hardwood with light pressure.
Barber chairs often cause great arousal among habitat managers who worry about the risk to the point that they create more risk by being too tentative in cutting trees. A good sharp saw with high torque and horsepower is your best defense against barber chairs. Partial cuts are likely to cause barber chairs with greater energy. It is better to cut quickly through the stress points, get far enough to release the tree, and then get out of the way. If you are not creating wood chips about the size of the inside diameter of the saw tooth, you need to stop and sharpen your saw. You should not be creating sawdust; you should be creating wood chips! This is critically important.
Where does the most danger come from?
Barber chairs are a great concern and every precaution should be taken to control risks while doing hinge cutting, but they are not the greatest source of risk.
1. Fatigue. When your arms and legs start feeling heavy, it is time to put the chain saw away and do something else. Fatigue will injure or kill you faster than anything else.
2. Dead limbs overhead and dead trees that are being held in place by the tree you are cutting–sometimes indirectly, so you really have to look carefully for them. (common risk both to loggers and hinge cutters)
3. Slingshot debris from downstream. When you release the tree, it will bend downstream trees, and then often release them like a catapult. Anything in those trees that is loose is going to fly back in your direction. You can be 20 feet behind the tree and get hit by 100 lbs. of flying wood that was in the tree beyond the one you cut. (common risk both to loggers and hinge cutters). Even a 1 lb. piece of wood can kill you, especially if you are not wearing a helmet.
4. The complete release of the butt of the tree that can occur when the top hits the ground or when the split itself shears off the tree. This will send the butt of the tree flying and you don’t know where it is going to land.
5. The hinge itself hitting you prior to the tree falling. In my view this is still important but is much less likely to hurt or kill you than the above 4.
Ash, walnut and other straight-grained trees are especially prone to barber chairs (Figure 11).
Figure 12. Ash trees hung up. We pulled these trees down to the ground with a come-along.
When hinge cutting a leaning tree, I have found it best to cut straight across the grain. It is the shortest path to releasing the tree (Figure 12). The farther the tree is leaning, the greater the tension on the cut side, and the greater the risk.
Figure 13. Cut straight across the grain of leaners.
Reading the tree.
I have talked above about energy distribution in a tree. It is critically important to understand where the compression and tension are on the tree you are cutting. This is one of the things that is toughest to figure out when you are starting out. You will be standing next to a tree that appears to be leaning quite a bit, and go to cut it, and get your chainsaw pinched so hard you can’t get it out–too late to even get a wedge started. The reason is that the direction the base of the tree is leaning has only a fraction of the influence, as the direction the crown wants the tree to go. It is simple leverage. As you go up the tree, the influence on the direction of the fall grows exponentially. For example, you could be 7/8ths of the way through a tree and think it is ready to go. You could push on it as hard as you want and it might not go. But if you could push with 1/100th the force on the top of the tree it would go right over. That is why the top of the tree (the crown) is the main decider of where the tree “wants” to fall. Where the trunk is leaning has a relatively minor impact.
The guy in this diagram (Figure 14) is on the wrong side of the tree if he wants it to fall where it naturally wants to go. It wants strongly to go to the left. There is a lot of force being exerted by the top of the tree to make it go left, even though the trunk is leaning towards the right. It “feels” from the ground like the tree wants to go to the right. You need to stand back and circle the tree and look at major limbs and the crown of the tree to determine where it wants to go.
Figure 14. The tree in the diagram wants to fall towards the operator. The crown of the tree and the limbs coming off the left side are creating compression on the left, and tension on the right.
Safety—the number one concern.
If you don’t feel completely comfortable doing something with a chainsaw, don’t do it until you do feel comfortable. Timidity is not a good mind set to approach cutting trees. You need to know what you are doing, have a good idea of what the tree wants to do, and be prepared for it to do something else. Here are some items you should be using.
- As small and light a chainsaw as will accomplish the work. The number one cause of accidents is lack of attention, which is the offspring of fatigue.
- Use a sharp chainsaw. When you are going to cut, cut, don’t sand paper your way through or you will not be able to cut past areas of tension fast enough.
- Wear a helmet, ear protection, chaps, leather gloves, steel-toed boots, and goggles and/or a face shield.
- Always have an escape path with clear ground angled back 45 degrees behind the tree for about 20 feet or more. Head to your safety spot while still watching the tree. Stay in that position for several seconds after the tree hits the ground while watching upwards for debris.
- Study before you cut. Look for overhead loose debris, leaning dead trees, and downstream dead limbs and debris in trees that may be hit by the one you are felling. You need to know the locations and direction of tension and compression in the wood, whether it be a tree or branch. A two inch spring branch, that is, a branch or tree that is trapped and under tension will kill you in a second if you are behind it when it is released, and a helmet probably won’t help any more than it would if a major league designated hitter made full contact with a bat.
- Keep out from behind a cut tree as much as possible when wedging or pushing it.
- If you feel any uncertainty, don’t cut the tree.
- Go to the OSHA website and carefully read everything they have to say about cutting and bucking trees. http://www.osha.gov/SLTC/etools/logging/manual.html