The Principles of Weed Trimmers Content from the guide to life, the universe and everything

The Principles of Weed Trimmers

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Trimmer - A mechanical device used to cut grass and weeds in places that a conventional mower cannot.

A 'weed eater' has three main parts:

  1. Mower
  2. Connector
  3. Engine

The Mower

The Mower is located at the bottom of the trimmer and performs the actual cutting of the grass. This section houses two main parts: the shield and the cutter.

The shield's function is to protect the user from being hit by flying debris, as well as regulating the string length with a blade on the edge of the shield. When the string is propelled against the blade, it is cut to accommodate spinning inside the circular shield.

The cutter's main function is to cut the grass, weeds, or other material it is guided to. It cuts by spinning either blades, or nylon string at a very high velocity in a circle. The velocity at which it travels can be altered via the connector's trigger.

The Connector

The connector is located between the mower and the engine and is used to guide the mower segment to whatever place you want. There are four main parts to the connector section: the rod, the handle(s), the trigger, and the shut-off switch.

The rod is a long, hollow metal tube that connects the mower to the engine. Inside it run the wires for the electrical controls, as well as the drive shaft for the cutter. The rod can have different shapes (some are just a straight rod) which can be very rigid or very flexible. Others are curved downward at the mower end of the rod to provide the user with comfort while trimming. The handle is located about halfway up the rod and the trigger is either located halfway between the handle and the engine or on the far handle, depending on the type of handle you get.

The handle(s) can be in two different shapes. However, both perform the same function - to guide the mower in the correct direction. The more common shape is a circular hoop, which can be used to control the mower with one hand. In this case the trigger is located halfway between the handle and the engine. The more expensive, yet more efficient handle is one that has two quarter loops extending from the rod, one left and one right. This creates a 'U' like appearance of the handles, and in this case the trigger is located on the far handle.

The trigger's function is to control the velocity at which the mower's cutter spins. The trigger can be a hand lever, in the case of a hoop handle, or a push button, in the case of U-handles. The harder you pull on the lever, or push on the button, the higher velocity the mower spins, the more efficient the cutter works, and the more fuel is used.

The shut-off switch does exactly what you'd expect: it shuts off the mower. The switch is located near the trigger and can be moved to two positions, one of which will say 'Off'. The other position shows no words, when no gas can enter the engine, which keeps the engine from starting, or turns the engine off. The other position is 'Vice Versa' which keeps the engine from turning off. However, flipping the switch will not turn the engine on.

The Engine

The engine is located at the top of the trimmer and is used to spin the mower's cutter at high speed. There are many parts to the engine but only two are used: the primer and the pulley.

The primer is a small button located near the pulley. This button is used to put a small amount of gas into the engine for immediate combustion when the pulley is pulled. This allows for a much easier start when you first get the trimmer out, and also after you have run dry on gas.

The pulley looks like a string with a handle tied to the end of it. It looks like this because that is exactly what it is. The pulley is used to start the trimmer. The task of starting can be rather difficult, however, making sure to prime before starting it can help a great deal.


Now that you know the mechanics of a trimmer, you can successfully learn how to operate one. Here are the steps:

  1. Check - Make sure the shut-off switch is not set to off.

  2. Prime - Push the primer

  3. Pull - Pull the pulley with quick, hard, yet efficient tugs which extend the pulley to its max; it may take a few tries to get it started, don't give up!

  4. Squeeze - Squeeze the trigger in order to warm up the engine, you'll hear the engine roar to life. When you hear this, release the trigger.

  5. Guide - Move the mower section to the spot where there is grass and/or weeds. You may have to walk. The rod is not extendable.

  6. Squeeze - Squeeze and hold the trigger to obtain the desired speed while moving the head of the mower in a semi-circle fashion.

OK, so you started it, and you trimmed. Now how do you turn this thing off? It's easy. Just flip the shut-off switch and listen to the engine quickly get choked of gas and go unconscious, only to be reawakened by a string ripping him to life.


The price of a trimmer depends heavily on the quality of the engine, as well as whether it is nylon string- or blade-based, grips on handle(s), and size of shield. Another major price factor is brand name.


The maintenance of a trimmer is not necessarily all that much if you take care of your property. However, a few inevitable problems will arise. These problems include, but are not limited to, gas refills and string replacement.

Gas refilling appears to be a very easy thing. However, since there is no oil to refill, an oil-gas mixture must be used. The mixture of a trimmer is different for the different brands. However, the mixtures are all represented the same way. X:Y where X is the number of units of gas and Y is the number of units of oil. Therefore a 12:1 mixture would mean 12 units of gas should be mixed with 1 unit of oil, assuming the same unit is used for both.

Replacement string has proven to make refilling gas look like a walk in the park. The numbers of tries that must be attempted before a complete and successful re-stringing is achieved can not be counted. Add that with the stress of being entangled in the string you are trying to string with and one can begin to understand what is going on inside the head of the re-stringer. When you go to string a trimmer you must have the necessary supplies: a piece of replacement nylon string about two metres in length and more importantly a lot of patience. Here are the steps to successfully replace string.

  1. Remove the cap from the bottom of the cutter.

  2. Push the button on the bottom and remove the circular disk.

  3. Remove any small amounts of string left in the grooves of the disk.

  4. Take your replacement thread and double it up so that you have two equal length pieces connected at one end.

  5. Insert the connected side of the string into one of the slots between the two main grooves.

  6. Spin the disk in one direction while slowly allowing the thread to wind up on both sides in the same direction.

  7. Once you have wound most of the string leaving about 6-7 inches of each left, insert one of the strings into one of the upper slots take the other halfway around and insert it into the upper, opposite the one the other string is inserted into.

  8. Replace the disk where you got it from and fix the strings into the little holes that the string is fed out of, making sure to not let it go or else the string will unravel itself completely.

  9. Replace the cap.

  10. Woo Hoo! One successful restringing done; many unsuccessful ones to come.

Protection from:

Trimmers can be very dangerous if necessary precautions are not taken. Hundreds of incidents of the old 'that could poke your eye out' variety have come to life. And new incidents like 'that could poke your ear out, leg out, and arm out' have also been created. When weed-wacking most, if not all, of the below precautions should be used.

  • Goggles or protective glasses
  • Long pants, preferably jeans since they will stop most flying debris
  • Long sleeve shirt to protect your arms
  • Ear muffs to protect from flying debris as well as from the noise the motor puts out

Advanced Trimming Technique(s)

OK, we have all known the troubles of trimming - having to stop, pulling out the string, restarting the thing, and continuing again - which all proves to be a rather large pain. Well, worry no more; there is a way to feed new string without having to even stop the trimmer. Here's how. As you are trimming, when you notice that the string has worn down a considerable amount, simply find a rock or other hard surface and tap the bottom of the cutter on the ground. Magic! An extra inch or two of string will pop out for your immediate disposal. The technique has proved so useful, that the old technique of pulling out string by hand is now not even considered a technique! Now get out there, worry-free, confident in the knowledge that you're now an expert in weed trimming.

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