You can freely build on How the String Trimmer (Weed Eater) Actually Cuts Grass

What this patent covers

The patent defines a rotary cutting tool that uses a flexible, non-metallic line to trim vegetation. The core mechanism involves rotating this line at a specific tip velocity, calculated based on the line's thickness (diameter), to ensure it cuts grass effectively without being dangerous to the operator. The apparatus includes a housing that stores the line, allowing it to extend through an aperture while spinning. By controlling the relationship between the line's diameter and its rotational speed, the device achieves enough energy to slice through plant stems while remaining safer than a rigid metal blade.

What is now free to use

All 1 claims of US 3826068 are in the public domain. Specifically:

• Claim 1: Apparatus for cutting vegetation and the like — 1 specific element

The 0 dependent claims add narrowing limitations and are also free.

What is NOT covered

Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.

• Does not cover cutting tools that use rigid metal blades or discs.

• Does not cover systems where the line is not flexible or non-metallic.

• Does not cover rotation speeds that fall outside the specific mathematical range defined by the line's diameter.

• Does not cover manual or non-rotary cutting tools.

Who is building on this today

Major power tool manufacturers like Husqvarna (which acquired the Weed Eater brand), Stihl, Black+Decker, and Ryobi continue to refine the basic rotary assembly described here. These companies focus on improving battery efficiency, motor torque, and automatic line-feed systems that build upon the original rotating housing concept.

Products built on expired version of this technology

How to cite this patent in your documentation

Individual. US Patent 3826068. Rotary cutting assembly. Granted 1974, expired 1993. Now in the public domain.

Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.

PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.