Chainsaws are not only used in the forest, but increasingly also in private gardens. Unfortunately, if used improperly, these useful devices pose a high potential risk.
In the following we explain the purpose of an automatic chain brake as well as other alternative techniques to protect the user.
What is a chain brake anyway?
You almost think: a chain brake is used to brake the chain. In truth, however, it does a lot more: the chain is stopped in a flash. All saws stop in less than 0.2 seconds and not only stop the chain, but also the motor. Electronics and motor must interact here, as stopping just one of the components – chain or motor – is not sufficient for the safety of the user.
So the chain brake does more than what happens with a simple turn of the engine: it is an overrun of the chain prevented .
What is a kickback or “kick-back” of the saw?
Here we are dealing with a physical process that is easy to explain: if you look at the moving chain, you will notice that it is moving away from the user on the upper side and towards him on the lower side, i.e. from the side seen clockwise. At the point where the movement is reversed, namely at the tip of the sword, the chain moves downwards – even if only a few centimeters – and this has fatal consequences if the tip is touched on a branch or piece of wood.
In such a case, the saw, which is exerting a downward force at that moment, experiences a corresponding upward force according to the principle of interaction – kickback occursor “kick-back”, which can rip the whole saw out of your hands. If the chain continues to run at this point, it can cause extremely serious injuries to the user, and fatalities occur again and again.
Most modern chainsaws have a very pointed blade towards the front – this greatly reduces the area in which the chain runs downwards.
When and how is the chain brake triggered?
All chainsaws have a so-called hand guard or chain brake bar , which is the central switch for the chain brake. This chain brake bar triggers the chain brake in two ways:
- once by deliberately pushing forward with the left hand,
- secondly by touching the back of the hand or glove when the saw moves upwards (like a kickback) and the user still has his hand firmly on the second handle,
- and finally through the physical inertia of the hand protection, an effect that is called ” SafetyMatic ” on Dolmar and Makita chainsaws . Due to its inertia, the handguard cannot keep up with the saw’s sword which is quickly torn up and folds forward – which triggers the chain brake. So even if the user let go of the left handle in panic, the chain would come to an immediate standstill (less than 0.15 seconds!) Due to this SafetyMatic effect.
Why are there chainsaws without chain brakes?
This is related to the chain speed, among other things. If this drops below 3 meters per second, a chain brake is usually not installed and the device is delivered with a so-called tip protection , so that the user does not even run the risk of hitting wood with the tip. The efforts of the legislator are clearly in the direction of “chain brake for all chainsaws”, so that sooner or later this will become a norm. On the left you can see the Makita cordless chainsaw BUC122RFE. Makita has here on the installation of an autom. Chain brake dispensed with. Instead, the sword has a tip protector on the front.
In the commercial sector, chain brakes are fundamentally required, private users are in most cases obliged by the property owner or forest owner to use a saw with a chain brake.
All of the electric chainsaws presented by us are equipped with a chain brake, some of the cordless chainsaws are only equipped with tip protection.