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How Does an Automatic Feed String Trimmer Work?

The foundation that makes a string trimmer a distinct yet effective lawn care equipment is the string. The string, which is also known as line, is a special type of monofilament nylon that spins at an incredibly high speed to cut and trim weeds and grass in a yard.


The line, however, gets worn out while doing the job. This is why, a string trimmer has a spool of line that is fed to the cutting head as it operates. This is done with the help of the trimmer’s feed system.

What is a feed system?

In simple terms, a feed system is the mechanism that releases the string into the head. Since the string is made of a synthetic or composite material, it is prone to getting worn out from cutting down grass in a lawn. For this reason, a feed system is installed in string trimmers to effortlessly reload the string instead of manually pulling it whilst doing the job.

Types of Feed System

There are currently two types of feed system for best gas string trimmer on the market: bump feed system and automatic feed system. Both of which have distinct advantages and disadvantages. Let’s take a closer look at each type to understand them better.

Bump Feed System

The bump feed system is most commonly used on older models of string trimmers. The method requires you to literally bump the head of the trimmer on the ground to release more string. This type of feed system gives you more control over the length of the line to feed the head.


Automatic Feed System

An automatic feed system is an advancing mechanism that self-regulates string release whenever it starts to run short. Majority of string trimmers with an automatic feed also have an internal sensor component that gauges the length of the line. This type of system takes advantage of the centrifugal force from the spinning to automatically release a new line.

Advantages of Automatic Feed String Trimmers

Automatic feed string trimmers are now the most popularly used type of trimmer in the industry. This is because these nifty equipment have a lot of advantageous perks in comparison to bump feed string trimmers.

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  1. Best choice for beginners

    Automatic feed string trimmers are a more user-friendly type of trimmer. They are the ideal choice for people who are relatively new to the lawn care industry since they require less thought and effort.   
  2. Hassle-free feed system

    An automatic feed string trimmer automatically feeds string to the head when it starts to run short. Because you won’t have to constantly mind the string in your cutting head, you will have more chance to focus on the task at hand.

    In addition to that, an automatic feed system is less likely to break because you won’t need to frequently bump it onto the ground.
  3. Saves time during job operations

    Automatic feed string trimmers allow you to finish trimming faster because the string advances on its own. This means that you will not need to pause from time to time just to feed string into the cutting head.

How Does an Automatic Feed String Trimmer Work?

Automatic Feed System

The automatic feed mechanism works with an advanced internal component. This component gauges the length of the line in the cutting head. Once it has assessed that the line is about to run out, the automatic feed system is activated to automatically feed a new line into the cutting head, taking advantage of the centrifugal force from the equipment’s fast spinning motion to release and pull the line from the spool.

Automatic Feed String Trimmer

An automatic feed string trimmer is pretty much operated like other types of string trimmers in the industry, but with the exception of the feed system, of course. Unlike other trimmers, automatic feed string trimmers effortlessly and automatically release the string into the cutting head. There will be no need to bump it on the ground or manually pull the string out. Rest assured, this type of feed system does not compromise the effectivity and quality of the equipment. In any case, it is even considered as an upgrade from older string trimmers that make use of a bump feed system.

Trimmer Line Replacement

A downside to having a string trimmer with an automatic feed system is that it runs through the entire spool of line faster compared to a trimmer with a bump feed system. This is because the operator has less control over the feed. In these cases, knowledge about the proper way to wind a new line to the spool.

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Below is a step-by-step guide on how to wind a new line to the spool, including some tips and extra precautions in executing the task.

  1. Take out the empty spool from the string trimmer.
  2. Thread the end of the line into the hole in the spool.
  3. Wind the line tightly around the spool in the direction of the arrow.
  4. Leave an excess length before the other end of the line. .
  5. Place the spool back in the string trimmer.
  6. Feed the other end of the line into the hole in the cutting head.
  7. Place the cap to cover the spool.
  8. You’re ready to go!

Tips about Line Trimmer Replacement

  • Make sure that the end of the line is properly attached to the spool by inserting it through the thread hole. An image is shown below in order to guide you better.
  • While winding the line around the spool, make sure that you pull the line tight to create tension. This is to ensure that your line is not loosely winded.
  • Poorly wounded line results into excessive line feeding for an automatic feed string trimmer, so make sure that the line is not collected at one end of the spool nor is it wounded loosely around the spool.
  • Do not forget to cover the spool after placing it back in the cutting head. The cover helps protect the line from debris that might cause jamming.


Friendly Tip: If you are hesitant about line trimmer replacements, you can purchase pre-wound spools from your trimmer’s manufacturer. This can save you time and effort in winding your own spools. However, we have to warn you. Pre-wound spools are a tad bit pricey, so think about it thoroughly.

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