(Note: This is Part 1 of my Chainsaw Basics Series. In this article we will explore the terminology and concepts of what saw chain is, and how and why it works.)
How can I keep my chain nice and sharp? This was the question that I was faced with in the first few months in the trade. I saw other guys taking round files and passing them over the chains, giving them a good scratch. So I said to myself, “that looks easy enough, I can do that.” So I experimented with it, emulating what I saw other people doing. Sometimes I got good results, sometimes, not so much. I kept trying, with mixed results, trying to figure out why I couldn’t do it as well as others. Turns out, I was simply asking the wrong question. Instead of asking “why am I not very good with a file”, what I should have been asking was “why does saw chain work in the first place”?
In order to truly maintain something mechanical, you must understand how and why it works. Knowing how to change the oil filter on your car does not make you an auto mechanic. Why does the oil need to be filtered? Why does the engine need oil at all? What is “internal combustion”? Likewise, when I was picking up a file and dragging it over the teeth, I was engaging in what is known as ‘outcome-based education’ whereby, I figured that knowing the ‘how’ would be sufficient to get me the results. As it turned out, what was actually important was the ‘why’.
Chain: The Basics
Saw chain moves at incredible speeds. When it is sharpened and working properly, it appears to “cut” through the wood. However, saw chain is not designed to cut, it is designed to remove material, one chip at a time. Anyone who has ever used a hand planer will see the same concept on a chain saw:
– drawing courtesy of www.lie-nielsen.com
Now look at a cutter from a modern chain:
Why Saw Chain Works
So hopefully you can visualize the basic idea:
- each tooth acts as a tiny chisel
- IF: the chain is properly tensioned, the teeth are sharp, and the rakers are properly adjusted,
- THEN: as the chain spins round and round the bar, with each pass, each tooth will remove one wood chip.
- This is happening so fast that indeed it does appear to “slice” through the wood.
So, now that we have some context, lets look at what makes up a saw chain.
Overview of Chain Construction
Chain is comprised of several basic elements:
- Cutters – combination of tooth and raker
- Drive Links – allow saw to move the chain around the bar
- Cutters and drive links are held together by Tie Straps and Rivets
Teeth are arranged in alternating right/left fashion to help a chain cut evenly and straight. Depending on the length of the chain for a certain size bar, there will either be an equal number of alternating left hand and right hand cutters, or the chain will end with 2 back to back same-side cutters.
When purchasing a chain, there are three main elements to keep in mind, all of which will usually be stamped right on the bar of your saw. All three of these elements are concerned directly with the drive links of the chain. These three concepts are: Pitch, Gauge, and Number of Drive Links. In order to go around in a loop, the drive links of a chain ride on two sprockets: one is on the clutch in the saw, and the other is on the end of the bar. When you purchased your saw initially, the dealer would have made sure that these two sprockets matched, and that the chain, in turn, matched them as well. Let’s take a closer look at these three main elements.
Pitch is technically defined as the distance between any 3 rivets divided by 2, but this definition isn’t very intuitive, at least to me. What pitch is really measuring is the size of the drive links and the distance between them.
– drawing courtesy of www.rcpw.com
Gauge is just the width of the drive links where they fit into the groove in the bar. The gauge of a chain must match the gauge of the bar.
Number of Drive Links
This is how you match a chain to a certain length of bar. For instance, a 20″ bar migh be 72 drive links long.
There is one other major consideration to make when purchasing a chain, and that is concerned with the cutters themselves:
– drawing courtesy of www.rcpw.com
There are many different variations of cutter types, but among standard arborist round ground chain, we can simplify and say that there are 2 basic types of teeth: either the top corner is rounded or it is square. Chain teeth with rounded corners are preferable in dirty cutting conditions as they hold their edge better if you get into dirt. These are usually referred to as low-profile or semi-chisel. The more efficient and better performing type of chain is square-cornered or full-chisel. This is the standard chain type that professional arborists use the most in residential tree work.
The Cutter: A Closer Look
– drawing courtesy of www.rcpw.com
A modern cutter is the combination of a tooth and a raker. These two elements work in tandem to produce the cutting action – neither one on its own is capable of useful work in the slicing of wood.
Tooth – Top Plate and Side Plate
The front of the top plate forms the chisel edge, the part of the tooth that finishes the cut started by the corner. The top plate severs the wood chip, allowing it to be expelled.
The corner is where the top plate turns downward towards the rivets to form the side plate. The corner is the leading edge of the tooth and will make contact first with the wood, and so, the corner starts the cutting action of the tooth. To simplify, there are 2 basic types of corner – rounded or square.
The gullet forms the space between the actual tooth and the raker.
Depth Gauge (Raker)
The depth gauge, or raker, is what prevents the chisel edge of the tooth from biting in too much into the wood. The difference in height between the raker and top plate determines the depth that the tooth cuts with each pass around the bar.
Grind refers to the shape of file or grinding wheel that is necessary to sharpen each tooth. Standard chain is all round grind – it is sharpened with round files. There is such a thing as square ground which means that the tooth is filed using a flat file. Square ground chain is used exclusively among big timber loggers who cut softwood trees all day and it is beyond the scope of this article.
I hope this overview of saw chain has been in-depth enough without being overwhelming. Following up from what I said at the beginning, it wasn’t until I took the time to really learn about chain and how and why it works, that I was really able to service, maintain, and sharpen chains. Follow along to the next article to learn the finer points of sharpening saws.
Continue Reading, Part 2 in this series: Saw Chain Maintenance and Sharpening.
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