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How Saw Chain Works

March 12, 2017 By patrick@educatedclimber.com 8 Comments

Chain Line Drawing

(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:

Hand Planer– drawing courtesy of www.lie-nielsen.com

Now look at a cutter from a modern chain:

How a Cutter Works - Resized

 

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.

Chain Specs

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

Chain Pitch - resized

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.

 

Gauge

drive-link (removed detail)– 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:

Cutter Type/Profile

– 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

Cutter

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.

Corner

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.

Gullet

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

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.

 

Climb High, Work Smart, Read More.
– TreeMuggs

 

I would love to hear from you. Please send all comments/questions/hatemail  to patrick@educatedclimber.com

 

 

Filed Under: Arborist 101, Chainsaws

Overview: Tree Pests and Diseases

February 13, 2017 By patrick@educatedclimber.com Leave a Comment

Gypsy moth

Insect Pests

In southwestern Ontario, there are 5 main categories of insect pests that affect our trees:

  1. Defoliators
    a. Leaf Chewers
    b. Leaf Skeletonizers
    c. Leaf Miners
  2. Borers
  3. Sucking Insects
  4. Gall-makers
  5. Root Feeders

 

1. Defoliators

These pests feed on tree foliage – leaves of deciduous trees and needles of conifers. Because their effects are not systemic, the damage done by defoliators can usually be overcome by healthy, established trees. However, loss of foliage is still mild to moderately stressful on all trees, and if enough foliage is lost in one season, particularly in the new growth, it can spell disaster. The tree will have to use up significant amounts of reserve (stored) energy to make up for the loss of energy-producing foliage, and this loss of reserves can leave a tree vulnerable to many other stressors, both biotic and abiotic, especially if defoliation occurs several years in a row.

Defoliators are most commonly the larval (caterpillar or grub) forms of various moths, beetles, and sawflies. Because they are only feeding on foliage in the larval stage, their ability to damage trees is usually limited to a short time period in any growing season (2-6 weeks average). They are commonly broken down into 3 categories based on how they feed on foliage:

 

a. Leaf Chewers

The leaf chewing pests have the largest mouth-parts of defoliator larvae which allow them to eat large sections of leaf, sometimes devouring the entire leaf.

Common leaf chewers in southwestern Ontario include:

– Fall Webworm
– Gypsy Moth

Fall webworm  Fall Webworm Damage

 

b. Leaf Skeletonizers

The leaf skeletonizer pests are able to eat the soft outer tissues of foliage while leaving a skeletal network of veins behind, producing a very distinct visual effect.

Common leaf skeletonizers in southwestern Ontario include:

– Oak leaf skeletonizer
– Japanese beetle

Japanese beetle  Japanese Beetle

 

c. Leaf Miners

The leaf miner pests are very small, tunnelling unseen between the upper and lower surfaces of leaves, feeding upon the succulent interior tissues, again producing a distinct visual effect.

Common leaf miners in southwestern Ontario include:

– Birch leafminer
– Cedar leafminer

Cedar leafminer  Cedar leafminer damage

 

2. Borers

The boring pests attack mainly the inner bark and wood, although all parts of the tree from roots to buds are affected. The main effects of boring insects are deformity and weakening of tissues, as well as serious damage to the transport tissues that allow trees to move water, nutrients, and sugars (cambium). If the transport tissues are sufficiently compromised, decline and death will occur quickly.

Common borers in southwestern Ontario include:

– Emerald Ash borer
– Bronze Birch borer

Emerald ash borer  Emerald Ash borer damage

 

3. Sucking Insects

These pests have leaching mouthparts which they use to extract cell sap either from foliage or directly from transport tissue (cambium). Their effects are usually lack of vitality, wilting, or discolouration, but in extreme cases they are capable of causing serious stress, decline, and even death of plant tissues.

Common sucking insects in southwestern Ontario include:

– Aphids
– Oystershell scale

Aphid damage  Aphid damage

 

4. Gall Makers

These pests cause trees to produce distinct, abnormal growths which usually envelope the insect. Despite their conspicuous appearance, most gall makers affect the aesthetic value of trees as opposed to their actual health. Once the gall has formed around the insect, it is quite protected, making control or treatment very difficult.

Common gall makers in southwestern Ontario include:

– Ash flower gall
– Oak & Hackberry gall

Hackberry gall  Hackberry gall

 

5. Root Feeders

These pests live in the ground and feed on the succulent, non-woody portions of plant roots. They are seldom noticed and rarely cause the death of well-established trees. Seedlings or recently transplanted specimens with limited root systems are more susceptible to this type of injury.

Common root feeders in southwestern Ontario include:

– Black Vine weevil
– White Grubs

White grub  White grub

 

 


 

 

Tree Diseases and Disorders

Tree diseases may be defined as abnormal disruptions in the basic life processes of the plant, which may or may not be fatal. These disruptions are caused by parasitic agents (principally fungi but also bacterial or viral) or non-parasitic agents (nutrient imbalances, toxic chemicals, etc).

The presence of disease in trees is shown by the development of visible signs and symptoms. Signs are structures produced by parasitic agents (e.g. mushrooms, conks, fruiting bodies, etc). Symptoms are changes that occur as a result of injury (e.g. wilting leaves, discolouration, deformities, etc). Note that signs can only be produced by parasitic agents, while symptoms can be produced by both parasitic and non-parasitic agents.

Parasitic Diseases

The parasitic diseases of trees, of which most are caused by fungi, can be grouped into 2 main categories:

a. Foliar

Foliar diseases attack the foliage of the plant and are rarely transported inside the plant to other tissues. Their effect is similar to the defoliator pests in that the damage is rarely serious and trees can usually recover.

Common foliar diseases in southwestern Ontario include:

– Powdery mildew
– Anthracnose

Powdery mildew  Powdery mildew

 

b. Systemic

Systemic diseases are able to move within the plant, affecting not only the foliage, but also the cambium and roots. Because of their ability to attack the entire plant, systemic diseases are the most difficult to treat. Due to a lack of systemic fungicides that are approved for commercial use, pruning is often the only treatment available to help combat these diseases. Pruning of affected tissues can help slow the progression of disease but is often not enough to stop it.

The effects of systemic disease are often quite severe and can leave trees stressed and susceptible to attack by other organisms or lead to the outright death of the plant.

Common systemic diseases in southwestern Ontario include:

– White Pine blister rust
– Dutch Elm disease

Dutch elm  Dutch Elm disease

 

Non-parasitic Diseases/Conditions

In addition to pest and disease issues, trees can also be negatively affected by a host of other interacting biological and climatic factors. These include: air and water pollution, flooding, drought, soil compaction, grade changes, nutrient imbalances, adverse weather, temperature extremes, and mechanical damage, such as cutting of roots for construction projects.

When a tree is in decline it is rarely the result of one single issue. Quite often, a stressed tree has been assailed by many negative factors, both biotic and abiotic, that have left it with an energy deficiency from which it is too weak to recover. For example, a tree growing in poor, compacted soil with inadequate drainage will have difficulty overcoming defoliation by insect pests. In attempting to regrow its leafy crown, the tree will have to use up a significant amount of its energy reserves which will leave it vulnerable to attack by a countless number of fungal agents. The end result of all this stress is usually dieback of stems or branches. Trees in advanced stages of dieback rarely recover, typically succumbing to invasion by secondary pests and diseases.

Because of this spiraling effect of stress and decline, the best prescription for landscape trees is prevention, through efforts to maximize the health and vitality of the plant. A healthy tree is far less likely to be attacked by pests and diseases and if it is attacked, generous amounts of stored energy will help ensure the best chance of recovery.

Common non-parasitic diseases/conditions in southwestern Ontario include:

– Chlorosis
– Dessication (Winter Browning)
– Road Salt damage
– Dieback of Hardwoods

Chlorosis  Chlorosis

Road Salt  Road salt damage

 

 


 

Climb High, Work Smart, Read More.
– TreeMuggs

 

I would love to hear from you. Please send all comments/questions/hatemail to patrick@educatedclimber.com

 


 

Filed Under: Arborist 101

Tree ID Book Part 1- Southwestern Ontario

January 17, 2017 By patrick@educatedclimber.com 3 Comments

This is the Tree ID book that I made for the first part of apprenticeship school years ago. It is by no means all of the trees that you will need to know, but it is a good starting point. This covers 48 common trees in this area. This book does not do justice to either bark or buds, so it may not be all that useful for winter identification.

The only way to properly learn your trees is out in the field. You will not learn that much from a book, regardless of how good the book is.

Tree ID Book - Southwestern Ontario- PDF
Download as PDF

 

For a comprehensive treatment of all the trees that grow in this area, please refer to “Trees In Canada” by John Laird Farrar. This book must be considered required reading.

 

_____________________________________________

Climb High, Work Smart, Read More.
– TreeMuggs

 

I would love to hear from you. Please send all comments/questions/hatemail to patrick@educatedclimber.com

Filed Under: Arborist 101

Language Of The Ropes

January 17, 2017 By patrick@educatedclimber.com 7 Comments

If you are just starting out, you are going to need to know a lot of basic terminology. This will be a good starting point, and I will continue to update it as need be.

 

General

a. Rigging – use of ropes to lower and control sections of tree to the ground.

b. Rigging System – interaction of all elements used for rigging including points in the tree, slings, hardware, rope, force angles, etc.

c. Piece – the section of tree being rigged.

d. Rigging Line – main rope used to hold the weight of the piece.

e. Tag line – secondary rope used to control swing or directionality.

f. “Small Rigging” – piece can be carried or dragged by one or two people once on the ground.

g. “Big Rigging” – pieces that are too heavy for two people to carry, must be cut up once on the ground.

h. Positive/Overhead Rigging – rigging point is above the piece, used whenever possible.

i. Negative Rigging – rigging point is below the piece, used in the absence of other options, always involves shock loading.

j. Shock Loading – mass coming to a short, sudden stop. Can multiply peak forces by 10X or more.

k. Tension wood – fibers are being pulled apart.

l. Compression wood – fibers are being squeezed together.

m. Leverage – bending force being exerted at a distance from a fulcrum.

n. Mechanical Advantage – force amplification achieved by using a tool, mechanical device or machine system. In our line of work, this is usually achieved using ropes and pulleys, although there are other options, including come-alongs. Mechanical advantage always involves a trade-off: pulling distance for pulling power.

o. Friction – the force resisting the relative motion of solid surfaces sliding against each other. Friction produces heat which can damage both ropes/hardware as well as tree bark. Friction management is a key component to many aspects of tree climbing and rigging.

 

Hardware

a. Tensile strength / Minimum Breaking Strength (MBS): the average breaking strength of a piece of equipment when pulled to failure under controlled conditions. Tensile strength is usually quoted in kN.

b. Kilonewton (kN): approximately 225 lb.

c. Minimum strength: as defined by safety legislation and regulations, life safety gear is required to have a tensile strength of at least 5000 lb (usually rounded up to 23 kN).

d. Working Load Limit (WLL): expressed as a fraction of the tensile strength, this is the maximum load that the equipment is rated for over a large number of cycles. Standards are rigging gear 5:1, climbing gear 10:1. For example, if a rigging line is rated for 5000 lb and the working load limit is 5:1, that means you can consistently load it with 1/5 of its tensile strength (i.e. 1000 lb). For a climbing line rated at 5000 lb, you can consistently load it with 1/10 of its tensile strength (i.e. 500 lb).

e. Cycles to Failure: Ropes and slings can only be exposed to heavy loads so many times before they eventually fail. Adherence to WLL guidelines will ensure long life for your equipment, this is why it is so important to know the history of your gear.

f. Static Rope: very low stretch (0.5-1.5% range). Rarely used in rigging.

g. Semi-static Rope: low stretch (1.5-4% range). This is standard arborist rope used for climbing and rigging.

h. Dynamic Rope: very high stretch (5-20% range). Used in mountain climbing to catch a lead climber during a fall to minimize injury.

i. Bend Ratio: when running a rope through a block or pulley, the minimum ratio of sheave to rope diameter is 4:1. This means that if we are using 1/2″ rope, the sheave must be at least 2″ in diameter. A more preferable ratio, as recommended by Samson Ropes, is 8:1, for maximum strength retention of the rope, meaning that a 1/2″ rope would be used with a pulley sheave diameter of 4″.

 

Climbing

a. Moving Rope System (MRS) – Traditional climbing system, also known as DdRT (Doubled Rope Technique), wherein the climber’s line is terminated at their saddle, then run up and over a branch union (tie-in point), then back down to the climber and attached by a friction hitch (or mechanical device). From the friction hitch, the rope continues to the ground. This system forms a closed loop that can be made larger or smaller, thus allowing the climber to move towards or away from the tie-in point. Note that the entire length of rope is moving as the climber ascends or descends, making friction management an important concern.

b. Stationary Rope System (SRS) – Newer style climbing system, also known as SRT (Single Rope Technique), wherein the climber’s line is run up through a branch union (tie-in point), and either affixed to it directly, or run back to the ground where it is tied off. The climber is attached to the line by a friction hitch or mechanical device. In this setup, the climber can ascend and descend with consistent friction, as the rope remains stationary, i.e. the climber is moving along a fixed line.

 

_____________________________________________

Climb High, Work Smart, Read More.
– TreeMuggs

 

I would love to hear from you. Please send all comments/questions/hatemail to patrick@educatedclimber.com

Filed Under: Arborist 101

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