Understanding the Chainsaw Chain Brake


It does not need to be said that chainsaws are incredibly dangerous tools, deadly even. Their use absolutely necessitates careful operation and a keen eye for safety. Luckily, their operation is made substantially safer with a mechanism known as a “chain brake.” The chain brake of a chainsaw is a pressure-activated switch that abruptly and suddenly brings the movement of the chain to a halt, preventing injury or unfortunate accidents.

Despite it being such an important and necessary mechanism to understand, many chainsaw users are unaware of their true purpose or when to use it. In this article, we will focus on de-mystifying their use and open your eyes to the true use of a chain brake and why you should never be afraid to use it. Let’s start with the basics.

What is a Chainsaw Chain Brake?

To answer the question of what a chain brake is, let’s first discuss what it is not. A chain brake is NOT an anti-kickback mechanism. While this may be a potential saving grace in the event of extreme kickback, this is neither its sole intended purpose nor its most effective use. Instead, it is like the safety switch on a gun. The chain brake is a user-activated switch in front of the engine and behind that bar that prevents the chain from moving at a time when it is not intended to be moving, even if the throttle is engaged. Thus, it is used to arrest any potentially dangerous accidental activation of the saw. This is primarily how it is used.

However, it does also serve as an emergency brake by potentially being activated by your hand or wrist if the chainsaw were to suddenly kickback toward the user. We will discuss this auxiliary function later.

How to Use the Chain Brake

Using the chain brake is a very simple process. To engage the chain brake (meaning the chain is prevented from moving, simply push the lever forward with your fingers, such as in the picture below. When engaging the chain brake, it should only take relatively light pressure before the lever snaps forward and instantly engages.

Engaged Chain Brake
Engaged Chain Brake

To disengage the chain brake, simply pull the lever back with your fingers, such as in the photo below. Note, however, that when disengaging a chain brake, there will be considerable slack in the mechanism, and the lever must be pulled back fully before the brake snaps back into a disengaged position. This slack is normal, as it prevents accidental disengagement and also allows for easy activation in the event of emergency.

Disengaged Chain Brake
Disengaged Chain Brake

When Should a Chain Brake Be Used?

As stated previously, the chain brake is like the safety switch of a gun, and it should be used similarly. The chainsaw brake should be engaged whenever the user takes a hand off the saw or takes more than a single step. The only time the chain brake should be disengaged is when you are actively cutting or cutting is imminent. Following that simple rule will ensure the chain brake keeps you safe to the best of its ability and will do much to prevent unfortunate, even tragic, accidents.

The Chain Brake as an Anti-Kickback Mechanism

Of course, the chain brake does have an alternative use as an anti-kickback mechanism, and this is what most people recognize it as, but it should not be seen as its primary use.

It works like this: If the saw were to suddenly kickback and rise toward the user, the user’s wrist or hand would catch the chain brake and pop it forward (This is why it snaps forward), engaging the brake system and bringing the spin of the chain to an immediate halt.

You can see a mock up of how this situation might unfold in the image below.

Activating the Anti-Kickback Mechanism
Activating the Anti-Kickback Mechanism

In such a situation, the chain brake can truly be a life-saving device, but will it always work?

NEVER Depend on the Chain Brake to Protect You From Kickback

Though the brake may work as an anti-kickback device, you should NEVER depend on it. The reason is simple: It doesn’t always work. Fortunately, I’ve never had an occasion where I needed this mechanism, but trying to replicate it with the saw off, it is quickly evident that its function requires a fair bit of luck. Your hands and wrist may not always be in a position that would activate the brake properly. In fact, looking at the image above, you can see I almost have to deliberately manipulate my wrist in such a way to hit the brake.

Thus, the chain brake should be your LAST line of defense against such a scenario. Instead, it is much better to educate yourself on the causes of kickback and avoid them. In particular it is important to avoid cutting with the “kickback zone” of the chainsaw bar, as illustrated below. Cutting with this part of the bar is the primary cause of kickback.

Kickback Zone

How It Works

Now that we have an understanding of what they are and how they should be used, it is worthwhile to discuss briefly exactly how the chain brake of a chainsaw works.

The brake itself is just a band of metal that wraps around the sprocket clutch drum, constricting its ability to rotate with immense amounts of friction. When the brake is engaged, a spring mechanism tightens the band. You can see the mechanism on the back of the clutch cover below.

The chain brake behind the clutch cover.

Because the mechanism is entirely in the clutch cover, the brake MUST be disengaged when the cover is removed. Otherwise, the band will tighten beyond the diameter of the sprocket clutch drum, and it can be difficult if not impossible to get it back on. Forgetting this detail can lead to quite the headache, so its helpful to keep it in mind when disassembling your saw. A bit of complication in maintenance is a fair price to pay for such an important feature.

The Chain Brake Is Crucial

If there is one takeaway from these words, let it be this: knowing and PRACTICING how to properly use the chain brake is imperative for the safe operation of a chainsaw. Next time you go out to cut trees or firewood, consciously make an effort to use the brake like you would a safety of a gun. Always engage the brake you take a hand off the saw or take more than one step. Perhaps most importantly, be sure to use a chainsaw equipped with a brake. While virtually all saws come stock with them, there are still older saws floating around in garages that have no such mechanism. If this is you, do yourself a favor and get yourself a new, modern saw–Maybe a new pair of chaps while you are at it. You owe it to yourself and your loved ones. These tools are not something to be taken lightly. Be safe!

Zachary Lowry

A forester from northern Maine, I spent my early career working for large timberland owners, managing forest land and investments in the form of managing timber harvest operations as well as planning and managing precommercial thinning, planting, and herbicide application programs. These days I work on my own land and help timberland owners large and small manage theirs.

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