Friday, January 22, 2016

Stump-Shot or Not....


Stump-Shot or Not...



By Tim Ard, Forest Applications Training, Inc.


You've made an almost picture perfect face notch in the tree trunk. Right on dimensions and directed perfectly for a spot on placement of the tree in the drop target area. Now for the back cut to finish off your task. 

You level up the saw bar with the proper height on the back of the trunk, ready for the final cut. But wait, what’s your thoughts on where the back cut should be height wise in relation to the V of the face notch. Should it be higher than the V, or lower? And if so, how much should it be higher or lower? One inch, two inches or three inches. 

Stump-Shot or in other terms the correct raised offset level of the back cut on a limb or tree has been tossed around for as long as there has been saw work. The Stump-Shot has been always used in felling, and sometimes large limb removal, to keep the severed piece from rebounding backward toward the operator. It is kind of a physics thing that when a tree or limb is severed it tends to fall (unique concept huh). When it falls the center weight of the stem seeks its attachment point and the butt end comes backward during that action. This backward action is believed to be limited by the Stump-Shot. The higher back cut leaves a ledge to limit the stem from coming back during that rebound action. It locks the butt so to speak on the Stump-Shot so it’s less likely to come back. 

In reality this action of butt rebound starts when the felling hinge is broken or no longer controls the fall. This happens in timing with the action of the face notch. If the notch is closed the hinge breaks. The vertical position the stem is in during the falling process when the hinge control is lost causes the butt rebound to be greater. In the fall of a virtually straight tree, if the face notch is 45 degrees this takes place at a position of half way to the ground. If the notch is less that 45 or the notch is by-passed (back corner of the notch does not meet exact), it could take place sooner in the fall. Either way some amount of control is lost in the tree fall when the notch closes or resistance breaks the hinge. So, the Stump-Shot it is believed to assist the hold of the stem in position on the stump during the fall.

Another way to think through the process is to think what would keep the stem attached to the stump longer and possibly more predictably?  If the face notch were open to 70 degrees (the Open Face technique) or even more, then the stem would stay attached until such time as the butt rebound scenario is not a factor. This more open notch, allowing the hinge to remain in intact longer, retaining control of the fall until the tree or limb is to a desired position on the ground. If the tree hangs on something the hinge is most likely still holding. Butt rebound becomes little or no factor.

But why not just use a Stump-Shot to make sure? Three things come into play.

  1. To be sure of the hinge dimension you plan to control the tree or limb movement with is to have the back cut level to the face notch. Often limbs and trunks grow with angled fiber, like a flared trunk at ground level or a limb collar up the tree. Think about if you have fiber growing at 30 degrees and you consider the level of a notch and the higher level of the back cut. Your planned hinge thickness between those two levels, because of the angled fiber between, could be reduced unknowingly between those two points. Knowing this scenario the only way you can plan/calculate an exact hinge thickness or width is with your back cut level to the notch.
  2. When the tree or limb starts to fall with a Stump-Shot it has to separate fibers vertically to begin the hinge breaking process. The Stump-Shot can cause splitting of the log and loss of control if the hinge is not to a bendable dimension. If the hinge is thin at the Stump-Shot level it can cause the tree to twist or set down during vertical fiber separation losing direction steering control. When the hinge is level to the notch the fiber is more apt to break from the back to the front without pulling fiber from the stump or log. If the side weight tries to break the hinge it is usually better supported by end grain fiber of the stump.
  3. The Stump-Shot doesn't keep the tree from spinning or going off toward side weight and coming backward. If contact with another tree or limb takes place, after the notch has closed and hinge is broken, the control of the tree is not maintained by the Stump-Shot. It can still butt rebound. Smaller trees can roll off the Stump-Shot quickly and still butt rebound. 

So in conclusion there is nothing wrong with a calculated Stump-Shot in your plan, but just as with any part of a plan or technique, understand its limitations and its advantages. Success and safety is applying the right tool or technique from the plan bag and being totally aware of its purpose and or function. 

The Hinge is Your Friend! Make sure your notch allows the planned hinge to work properly during the fall and your back cut type and level maintains your ability to establish your hinge and move safely to your planned escape area as soon as the tree or limb begins to move. 

Always check your Chainsaw as per the Manufacturers Operators Manual and wear Personal Protective Equipment when working with a chainsaw in any operation.


For more information on formulating a work plan for you and your chainsaw — visit www.ForestApps.com or contact our office at 770-543-9862 or email info@ForestApps.com to arrange a training program for you or your organization. 

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