String trimmers are generally marketed with two basic types of shafts: those that are long and straight and those that are shorter and curved. In considering the best type of shaft, straight or curved, you should consider whether you will be using your trimmer to groom your own lawn or if you are a lawn maintenance professional. You also need to think about the nature of trimming and the durability, weight and cost of the trimmer.
Lighter, generally less expensive trimmers with curved shafts are generally best for limited, lightweight use. Heavier, generally more expensive trimmers with straight shafts are considered a better choice for extended, professional use. Trimmers with straight shafts are usually more powerful and better for heavy-duty trimming chores. Trimmers with straight shafts vibrate less, reducing fatigue by users during extended use.
Testers for "Popular Mechanics" report that the extra length of straight shafts puts more distance between the operator and potential flying debris. It also makes it easier to trim under overhanging tree branches, shrubs and other places that are difficult to reach. It is easier to avoid scalping a lawn when using a lighter trimmer with a curved shaft.
An agronomist at the University of Arizona Cooperative Extension Service says that straight shaft models are likely more durable because the drive cable does not have to flex as much as those on a curved shaft. They also weigh more than trimmers with curved shafts; this additional weight means that they vibrate less, and this extra smoothness of reduced vibration makes the parts last longer.
Ease of Use
Trimmers with curved shafts are lighter and easier for smaller persons to use. Some users prefer shorter, lighter curved shafts because they find them more comfortable. Since straight shafts are usually longer and heavier, they are better for taller, stronger persons.
Whether you get a straight or curved shaft, "Grounds Magazine" recommends a model with a strong, reinforced flex shaft. A quality flex shaft will absorb vibration, making your trimming chore more comfortable and preventing damage to the gears and clutch.