Читать книгу Chainsaw Manual for Homeowners - Brian J. Ruth - Страница 24

Pinch can be one of the most frustrating problems when cutting with a chainsaw. It happens when the saw’s guide bar and chain literally get pinched in the wood (right). A pinched chain can also push back and kick back.

CAUTION

When trying to remove a pinched guide bar, do not use a second chainsaw to “cut out” the first one. The second saw can get pinched or damaged when it hits the first saw. Also, do not try to pull, twist, or force the saw out as this could cause damage to the bar and chain. There is a “correct” way to free a pinched saw using a second saw—see here.

How does pinch happen? Often it is when cutting down on a section of log that is supported on both ends (below). A log that is supported this way is under a lot of compression stress on the top side and tension stress on the bottom side. As you cut down from the top, the center of the log will drop before it is cut completely through. This closes up the kerf and pinches the bar and chain.

This log is supported by brush on both ends and a prime candidate for pinching the guide bar.

The guide bar is pinched halfway through the cut. Tugging on the saw to free the bar has pulled the chain out of the bar slot.

Making angled bucking cuts

When a section of trunk is balanced in such a way that one cut section is likely to remain stationary while the other falls toward the guide bar, make the two bucking cuts at an angle to prevent pinch.

Make the first cut from the top, angling it downward toward the section of the tree that will remain stationary. Saw one-third of the way through the trunk. To sever the pieces, cut up from underneath at about the same angle.

PINCH PROBLEM:

When cutting down into a log supported on both ends, the kerf closes up and pinches the bar in place.

PINCH SOLUTION:

The best solution is to lift the branch or log to relieve the pinch and then remove the saw. Shut the saw off, then use a second tree branch or sturdy sapling as a lever to lift the log and relieve the tension, as shown at left.

Next, carefully lift out the pinched saw, left.

As a last resort, you can use another saw to cut near the original cut to free the pinched saw. Make a small cut down from the topside about one foot away from the pinched saw, below left.

Make a cut up from the bottom of the branch or log to meet the small top cut, below center.

The shorter log should fall away easily. With the pressure off the bar, the pinched saw can be lifted out of the kerf, below right.

Recruit a friend with a strong back to fit a pry pole under the problem log.

As your helper lifts the pry pole, carefully remove the saw straight out of the kerf.

Staying clearly away from the pinched saw, make a small top cut down from the top.

Align the bottom cut with the small top cut.

The small, lightweight log will fall away, freeing the saw.

PINCH PROBLEM:

When felling a tree or cutting down a stump, the kerf closes up and pinches the bar in place.

When cutting down the stump shown in Chapter 5, the guide bar became pinched in the kerf.

PINCH SOLUTION:

Shut the saw off. If the guide bar is in far enough to allow it, drive one or two wedges in behind the bar to free the saw.

I placed a wedge in the kerf and tapped it in with an ax. The saw itself is hidden behind the trunk in this photo.

The wedge opened up the kerf enough for me to withdraw the bar, start the saw, and finish the cut.

WARNING

If your saw becomes pinched while you are making the felling (back) cut, you know that the tree has started leaning the wrong way, and is now in danger of falling the wrong way. Use the pull rope, if you had the foresight to place one in the tree, to correct the lean toward the direction of fall. If no rope is in place, pound wedges into the cut to correct the lean. If you don’t have a rope in place, or wedges at hand, then you must call a professional for help. Keep yourself and everyone else far away, because the tree may fall at any time. You are in a very dangerous situation, without the tools to extricate yourself.

Kickback Guard

I have already mentioned the importance of preventing kickback in this chapter, and I will be mentioning it a number of times throughout this book. And most owner’s manuals will spend pages on it. That is because it is probably going to happen to you. I know of few chainsaw operators who do not have at least one kickback story.

Manufacturers have developed features such as safety chain and bars, chain brakes, and tip guards, but there are still thousands of kickback injuries every year. Kickback is like lightning—it strikes without warning and is faster than human reflexes can react.

A millwright and part-time chainsaw operator who suffered a severe chest wound from a kickback invented the Centurion Safety Guard. His invention took a different approach to the problem in the hope it would spare others from such an injury. The Centurion will not prevent kickback, but it does provide a barrier between the operator and the cutting chain.

The system is remarkably simple, inexpensive, and lightweight. It is based around a solid steel alloy bar attached under the bolts holding the sprocket cover plate. The flat steel bar extends nearly the length of the guide bar and chain, and about two inches above the top of the chain. In the event of a kickback, you would be struck by this metal bar instead of by the chain, thus protecting you from being cut.

The bar is spring-loaded and a hinge allows it to be in its safety position for normal cutting (see here) or locked upright at ninety degrees for undercutting (see here) or to allow cleaning and chain sharpening.

Top cutting with Centurion in safety position.

Undercutting with Centurion in the up position.