Most tree folk would agree that few experiences are more frustrating than fueling and oiling a chain saw, having it start up fine and run well, then discovering that it will only gnaw away at the wood, producing much dust, but little progress.
Not only are chain saw sharpening issues an efficiency problem, causing tree crews to spend far too much time trying to get wood on the ground or into the truck, they are also a safety issue. Working with a dull or poorly cutting saw not only means the operator is spending too much time thinking about how bad the saw is, but also that the saw is taking an actual physical toll on their body. A poorly or improperly sharpened saw will have excessive vibration and require greater user effort to cut with, making for more fatigued operators who may not have the energy or quick reactions they need when they most need it.
In addition, if a dull saw takes too long to make a cut, or makes it hard to match cuts up, the likelihood is that something may not go as planned in the always complex world of tree work.
The simplest solution to all these problems would be well and properly sharpened chain saws, yet most tree companies would freely admit that they have almost as many sharpening techniques as they have employees. A little information and knowledge of the basics of sharpening within the manufacturers’ guidelines may assist in the sharpening dilemma, and though there are certainly advanced and task-specific sharpening methods, the best way to get there is to start with the basics.
Attention to detail, consistency of pressure and angles, and an understanding of the function of cutter teeth are all key elements to properly sharpening a chain.
Files that are too large or small will damage a chain, possibly weakening it, along with not sharpening it well, so the right size file should always be used. The information about required file size should be readily available from the shop or even on the box the chain came in, but a general guideline is that the correct size file should extend about 20 percent above the cutter tooth. Typically, cutter teeth should be filed from the inside out, thereby avoiding all those filings going down into the channel of the bar; and it is typically more efficient to file all the teeth on one side of the chain, and then the other.
In general, unless an “all-in-one” file guide has been used, the cutter teeth should be sharpened on both sides using the right file and gauge, and then each individual depth gauge tuned with a flat file to its respective cutter tooth with a depth gauge guide.
The use of vises, either truck/chipper-mounted or a stump vise, will assist greatly in the sharpening process, holding the bar and saw still while letting the chain rotate freely between teeth.
For crew members with short-term memory issues who forget which tooth they started with, a marker in the sharpening kit to mark their starting point will be helpful, or always start the chain at a recognizable point, such as a double tooth. The diagonal mark running across the top of many currently available cutter teeth is known as a witness mark; and though it is intended to let operators know when to take the chain out of service, it also approximates the filing angle and can be used as a general visual guide. If the operator believes they have sharpened everything correctly, yet their cuts continue to bend and wander, they may wish to check the bar for tweaks or distortions. This is easily done by laying it on a flat surface or by looking down the rails for curves.
Depth gauges, often called “rakers” or “drags,” are not only extremely important to how well or poorly a saw cuts, but also one of the most often neglected parts of the sharpening process. This humble piece of metal pounds its head into wood fiber, and sadly sometimes dirt, for cut after cut simply to set up the size of the bite that the cutter tooth takes.
If the depth gauge is too high, the cutter tooth will barely or not even touch the wood, too low and the cutter tooth will take far too large a bite leading to chattering, especially in hardwoods, and possibly kickback. The closeness of this relationship means that each depth gauge should be filed in relationship to its particular cutter tooth. This should be done with a flat file, once again from the inside of the bar out; and though traditionally it has been a process of “just taking a little bit off” each time the chain was sharpened, the use of a depth gauge guide will make sure that each individual depth gauge is tuned for its individual cutter tooth, leading to a better cutting experience. A depth gauge and cutter tooth that are both sharpened correctly will result in nice fat chips of wood fiber with minimal chattering or bouncing.
The cutter teeth are the ones that actually sever the wood fiber chip by chip, after being properly set up for the right size bite by their respective depth gauges. The point or starting corner of the tooth begins the cut by entering the wood, the top plate and attendant angle begins to chisel a chip of wood down into the gullet as the side plate of the tooth separates it.
The design for modern chain saw teeth is based on observations logger Joe Cox made while watching a beetle remove wood during lunch. Cox later went on to found Oregon Cutting Systems.
Chain saw operators who look closely at the chips their saw produces will notice that chip width is approximately the same as the distance between the outer edge of one side’s cutter teeth to the other side’s outer edge. This is because both sides work with one another to sever the chip completely. Damaged cutter teeth, whether it is by a material other than wood, such as dirt or stone, or simply severely dull from use, will show an obviously shiny surface along the top of the front edge. The first step in the cutter tooth sharpening process is realizing that the tooth will need to be filed until that shiny area is removed. Cutter teeth that have suffered major damage may be more quickly sharpened by using a flat file to remove the shiny area, nicks and lacerations they have suffered, and then following up with a round file and gauge for finishing.
Although many tree crew members may have their own personal opinions – often based on their own hard-won experience – on the best angle to file the top plate of the cutter tooth, the reality is that chain manufacturers spend a great deal of money and effort on research and development to give fairly specific guidelines on the angles for the variety of chains they produce. The person with the file in their hand obviously has control over which angle they use, even if it means ignoring the boss and the file guide, but manufacturers’ recommendations typically range from 25 to 35 degrees for the top plate, depending on use and the type of chain.
As mentioned previously, consistency of pressure and angles will assist immensely in sharpening teeth correctly and well; and one of the easiest ways to insure this accuracy and consistency is to use a guide of some sort. There are a wide variety available, ranging from simple ones that only hold the file and provide the angles, to ones that sit over the bar, and even to those that are intended to be “all-in-one” and sharpen the depth gauges at the same time. Personal preference will dictate which file guide works best for individual users, but some form of guide will definitely improve the efficiency of the sharpening process and, thus, the cutting action of the chain.
There is a great deal more to chain sharpening and care than has been discussed here, but this brief introduction to the process and the roles different parts of the chain fill should assist somewhat in lessening the level of frustration in the workplace. In addition, if a crew starts out with the same basic knowledge of how a chain works and how to sharpen it, perhaps they can work together to develop a consistent method that everyone will use, helping each saw cut well regardless of who sharpened it.
Editor’s note: This article was originally published in April 2011 and has been updated.