Tuesday, July 5, 2011

Stuck in the Storm

Stuck in the Storm


By Tim Ard, Forest Applications Training, Inc.

We have all been there...take down a tree or we’re removing a tree already down from a storm and begin to make a cut on the trunk or limb. The wood grabs our saw with a vengeance before we can complete the cut. Yes, it’s happened to me one time a long, long time ago (Right, it’s a lie. Maybe twice...). If you cut trees it’s a fact, you will occasionally get stuck. The challenge is to limit the occurrence's and you can if you understand why and plan well.

When you make cuts with a chainsaw you have to constantly take information on compression and tension. Compression is the side of the pressure or bind in the log or limb that will close the kerf cut, pinching your saw bar. Tension is the opposite side, the side that will open away from your bar during the cut or movement of the limb or log. These reactions, I will call them, can take place from side to side, up and down or even at some unexpected angles, as the weight and pressures in the wood are released. There are a few common scenarios to plan around.

Open Air

In this case the smaller log or limb is supported by air or it is simply a limb that is coming from the trunk and is not touching anything at the end. Its not supported in other words. The compression side is on the bottom of the limb. The Tension is on top. You can simply make a severing cut from the top and the limb falls.

Weighted

What if it’s a heavy limb? What if the limb has weighted branches to one side? In this case the limb may split or begin to twist as you cut and it still pinches your chain and or saw bar. You have to anticipate the movement and out-cut the separating wood fiber. A notch or deeper compression side kerf cut is important here.

End Support

The log or limb is touching or supported on two ends or two pivots. It has a downward movement potential between the two points of support. The wood wants to drop in the middle. Top compression is found in this scenario.

Side Object

If a limb or trunk is against a side object, like a tree or anything that is applying pressure on the piece sideways. This may also be determined to be a horizontal spring pole. The compression is going to be usually on the away from object side or the inner arc side.

Other Considerations

Pivots may be formed by objects or limbs supporting the limb or trunk above ground level. Back pressure can be formed by the limb or log being more vertical or up against something in the end pushing backward. There can also be situations formed by fences, cables, electric lines, etc that require additional caution and specialized training.

In all the scenarios above, and there are many more actual situations that can be met in the field, it is so, so, important to have a good planning process to assess the needs and dangers before making each cut. Hazards, Side Pressures, Up and Down Pressures, Back Pressures and the Individual Cut Technique must be confirmed.

Solution

Next, I’ve planned and decide to make a cut, why do I still get stuck? It could be because trees grow in circles.

Picture the growth rings on a round piece of wood. Every ring (in most climates) represents a year of growth. Each ring is supporting the growth of the tree or limb cylindrically. As you cut through from any side, according to the shape of the cylinder at that given point, you remove support fibers. When the weight or pressure over comes the strength of the growth ring a split or twist usually (will) occurs. This split or twist can also be accompanied by unsightly peels of bark and outer growth layers. Most often this combination causes pinches of the bar and saw chain.

I am convinced the number one thing that causes the stuck is the weight and pressures that move the wood piece during the cut, sometimes very quickly. Because limbs and logs grow in circles it is very hard to determine at what point in the cut the fiber will separate or twist. When this happens, stuck city....

When you make a straight cut into the round wood piece, the externally applied pressures in the growth rings begin to separate. They push outward at the side corners of the cylinder rings and this causes resistance and splitting of the fiber. If again there is weight or pressures, it can cause you to become stuck in these separating fibers.

You must always observe the compression and tensions working. However, a cut or notch on the compression side can reduce the chances of unexpected fiber release and movement. Understand that just a straight cut creates a kerf (slot) but if the piece can only move the width of the kerf, when it closes, other pressures are created at the end of the kerf. A straight cut will often relieve the bind or twist of the cylinder fiber but binds and pulls can still be expected. Also, think about that in the kerf there are end grain fibers that should they bind against your bar or saw chain are like vise jaws. Stuck city...

A very useful technique I have been shown to virtually eliminate the compression side bind is to use a notch, or even simpler the slide notch, on the compression side. A slide notch, just to a depth of as little as a couple growth rings, will relieve the outward pressure at the ring growth and stops the split and or fiber pull. Outcome - Less bar and chain pinches.

Please understand that storm damaged trees and limbs are heavy and often are twisted and loaded with pressures and binds. You need to be familiar with these issues before picking up the chainsaw. Personal injury or property damage does not offset the perceived savings of not calling a professional or seeking special training first.

Should you decide to DIY, please make the investment in Personal Protective Equipment to hopefully lessen an injury should an accident, unplanned event, occur. Visit www.Elvex.com

Good Sawing!

Tim Ard is President of Forest Applications Training, Inc., a training company for chainsaw safety and operations techniques. For more information on training send a question or request to info@ForestApps.com or visit www.ForestApps.com

1 comment:

Bex said...

I came across your blog in Google when trying to find examples of tension and compression. I have a chainsaw assessment in a few days and your post really helped make the tension/compression info make sense. Thanks! :)