There would not be much debate amongst tree pros that few things in daily tree care operations are more infuriating than a chain saw that starts readily, runs well, but cuts wood like a chronologically gifted man gumming his Jell-O at evening chow — lots of energy expended for very little results. A poorly or incorrectly sharpened chain is not only an efficiency issue, slowing down the pace of the workday for the entire crew, but also a safety concern.
Chains that are not sharp, or sharpened incorrectly, require more energy to operate; are harder through vibrations on the operator’s muscles, tendons and ligaments; and, depending on how incorrectly they have been sharpened, can even be more prone to dangerous actions such as kickback. In addition, operators who are focusing on how angry they are with whoever sharpened, or didn’t sharpen, the saw are not paying as much attention as they should to the motorized cutting implement in their hands.
Other dangerous situations can occur due to the inability to line up or set up cuts properly because of the poorly sharpened chains. Many felling or removal cuts require a degree of precision to work properly, and a badly sharpened chain is many things, but never precise. The easiest solution to this issue is correctly sharpened and maintained saws and chains. Any discussion amongst tree folks about sharpening methods and tools will reveal a wide variety of opinions and methods, some that are worthwhile and helpful, and others that are based on poorly thought out ideas or because “we’ve always done it this way.”
Some basic knowledge of how a chain cuts wood and how to maintain the proper angles, along with some of the tools available for sharpening, will assist tree people in determining which sharpening method not only works best for them, but can also minimize frustrating moments on the job. As mentioned, there are a number of methods and techniques for sharpening, many of them with value learned from on-the-job practice. This column will focus primarily on techniques and tools compliant with manufacturers’ recommendations.
Sharp chains consist of pieces/parts
At its most basic level, the proper sharpening of a chain means the sharpener has to have an understanding of how a cutter tooth removes wood, good attention to detail, and an ability to consistently apply pressure at the proper angles. A lack of knowledge or ability in any of these areas can make cutting with a newly “sharpened” chain saw a frustrating experience, not to mention dangerous.
Set ’em up — depth gauges
To a casual observer with no understanding of how a chain works, it might seem like the depth gauge, also referred to as the “raker” or “drag,” has nothing to do with cutting. However, it’s one of the most important areas in sharpening a chain saw effectively, as it sets up the cut, but it’s often neglected. The depth gauge determines how large a “bite” the cutting part of the tooth takes, so it must be filed or tuned in conjunction with the cutting parts of the tooth and with each individual tooth.
If the depth gauge has been neglected while the cutting surfaces of the tooth have been filed again and again to perfection, the saw will cut poorly, if at all, as the depth gauges keep the cutter teeth from even coming into contact with the wood. Conversely, if the depth gauges have been taken down too much in relation to the cutter teeth, they will be getting too large a bite, causing at least vigorous chattering and vibration while cutting in hardwoods, and oftentimes vicious kickbacks as the too large bite stops the chain for an instant, causing it to attempt to turn within the chain, throwing it back toward the operator.
Either variation of depth gauge sharpening – untouched or touched too much — is unacceptable for safe, efficient cutting. Fortunately, both are easily remedied through the use of a depth gauge guide. These simple tools allow the sharpener to easily “tune” each depth gauge to its particular cutter tooth with a flat file, assuring the proper distance exists, and generating the efficient removal of a nicely formed chip of wood.
The depth gauge sets the stage for the cutter teeth. These are the “beasts” of the chain, banging into the wood again and again at a high rate of speed, hopefully chiseling out a finely shaped wood chip with each impact. 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 of modern chain saw teeth is based on a logger’s observation of a beetle’s jaws and teeth in removing wood. This logger, Joe Cox, later went on to found Oregon Cutting Systems.
Close observers will notice that the width of a well-formed chip is consistent with the distance from the outer edge of a right-hand cutter to the outer edge of a left-hand cutter, as both work together to fully sever the chip. Cutter teeth that have come in contact with something other than wood – perhaps while the operator was “digging for clams” in the dirt — will show a shiny area along the front edge. A starting point for sharpening is realizing that the tooth will need to be filed until that shine has been removed. Severely damaged teeth may be more quickly sharpened by removing this area with a flat file prior to even beginning with a round file and guide.
The angle without a dangle
Many tree care professionals have their own personal opinion on the best angle to file the top plate, yet chain manufacturers themselves, after spending millions of dollars on research and development, give fairly specific guidelines on angles for each of the individual types of chains they produce. The choice of angle is obviously up to individual users, but the typical angles from manufacturers range from 25 degrees to 35 degrees, depending on the type of chain and its projected use.
Guides for success
Once again, the use of any of a variety of guides will ensure consistency and accuracy in sharpening the cutter teeth. There are file guides that simply hold the file and provide the angle; roller guides that have a built-in depth gauge guide, providing two tools in one; and file guides that hold the round file, provide the angle, and hold a flat file that files the depth gauge at the same time.
While individual opinions and desires will decide which type of file guide is used, personal experience has shown that for the vast majority of chain sharpeners some type of guide will improve not only the speed and efficiency of chain sharpening, but also the cutting of the sharpened teeth when put into use.
The general process
While it may seem obvious to most tree folk, personal experience has shown that it’s necessary to mention that different chains may require different size files. A file that’s too large or too small will sharpen the chain poorly, and can also damage it, perhaps leading to sharp metal objects flying around the work site.
The correct file size to use should be noted on the box the chain comes in, or is available from the manufacturer. A general guideline is that the correctly sized file should protrude 20 percent, or one-fifth, above the cutter tooth.
File the cutter teeth from the inside of the bar out to lessen the chance of filings dropping down into the channel of the bar. For efficiency, sharpen all teeth on one side prior to filing them on the other side. Unless an all-in-one guide is used, the typical filing process would begin with sharpening all the cutter teeth using an appropriate file, and then going through with the appropriate depth gauge guide and a flat file and “tuning” each depth gauge to each cutter tooth. A bench vise, or stump vise in the field, will hold the bar and saw immobile during the sharpening process while still allowing the chain to rotate freely.
Sharpeners that have difficulty remembering which tooth they started with might use a marker to darken the first tooth they sharpen; some chains may provide two right or left-hand cutters in a row as an easy starting/ending point.
Most professional-grade chain cutter teeth have a diagonal line running across the top plate at the rear of the cutter known as the witness mark. Though it is intended to inform the user of when to take the chain out of service, it also tends to match the desired angle to file the tooth at, thus providing a visual guide for sharpeners.
The use of bench or electric grinders in the sharpening operation can be quite advantageous, as it will speed the process, but tree care personnel who choose this method must be aware of the grinder’s proper use and setup. The use of the appropriate stones and angles is paramount, as chains are easily ruined or destroyed if sharpened with a grinder that’s set up improperly. Additionally, grinder operators must pay close attention to the amount of time the grinding wheel or stone is in contact with the tooth, as it is easy to overheat the metal, causing it to lose its temper and creating a tooth that will be impossible to further sharpen.
Proper chain sharpening should be a part of every tree company’s training and culture for both safety and efficiency reasons. While there is obviously a great deal more to the topic than the basic information discussed here, this introduction to the actions of the chain components along with some tools and methods for sharpening them can assist tree folk in achieving more consistent wood cutting. In the end, properly sharpened chains will help tree folk cut wood while lookin’ good.
Editor’s note: This article was originally published in June 2014 and has bee updated.