How the String Trimmer (Weed Eater) Actually Cuts Grass
This 1974 patent describes the mechanics of using a high-speed spinning plastic line to cut grass, replacing dangerous metal blades with flexible, non-metallic material.
Original patent title: “Rotary cutting assembly”
This 1974 patent describes the mechanics of using a high-speed spinning plastic line to cut grass, replacing dangerous metal blades with flexible, non-metallic material. Granted to Individual in 1974 with 14 claims and 86 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
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.
The gap
What does this patent NOT cover?
- 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.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
The inventors realized that if you spin a flexible plastic line fast enough, it gains enough stiffness and kinetic energy to act like a blade, but because it is flexible, it deflects upon hitting hard objects like rocks or fences instead of shattering or causing severe injury.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Weed Eater string trimmers
Electric grass trimmers
Gas-powered weed whackers
Commercial landscaping edgers
Why it matters
The bigger picture
This invention is the foundation of the modern string trimmer, commonly known by the brand name Weed Eater. It transformed residential landscaping by replacing heavy, dangerous metal-blade mowers with a lightweight, safer alternative that could reach tight corners and edges. It is a classic example of how a simple material change—plastic line instead of steel—can create an entirely new consumer product category.
Filed
January 8, 1973
Granted
July 30, 1974
Market context
Who's building on this
Companies in this space
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.
Market impact
This patent effectively launched the global string trimmer market, creating a multi-billion dollar industry for lawn maintenance equipment. It standardized the use of flexible line for trimming, shifting the industry away from dangerous metal-bladed devices and enabling the mass-market adoption of handheld trimmers for home use.
Claim 1 — Plain English
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.
The clever bit
The inventors realized that if you spin a flexible plastic line fast enough, it gains enough stiffness and kinetic energy to act like a blade, but because it is flexible, it deflects upon hitting hard objects like rocks or fences instead of shattering or causing severe injury.
What it does not cover
- 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.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Moderate
Citation count
39/40
Highly cited
Claim breadth
9/20
Moderate scope
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$50K – $158K
Midpoint $99K · expired or expiring · industry ×2.2
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Patent Claims
1 independent claim · 0 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
14 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Ballas, G., & Geist, T. (1974). How the String Trimmer (Weed Eater) Actually Cuts Grass (U.S. Patent No. 3,826,068). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/3826068/weed-eater-string-trimmer
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How the String Trimmer (Weed Eater) Actually Cuts Grass cover?
This 1974 patent describes the mechanics of using a high-speed spinning plastic line to cut grass, replacing dangerous metal blades with flexible, non-metallic material.
Who owns patent US 3826068?
Individual owns this patent, granted in 1974.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 3826068 cited by?
This patent has been cited by 86 later patents that build on its ideas.
What problem does this patent solve?
This invention is the foundation of the modern string trimmer, commonly known by the brand name Weed Eater. It transformed residential landscaping by replacing heavy, dangerous metal-blade mowers with a lightweight, safer alternative that could reach tight corners and edges. It is a classic example of how a simple material change—plastic line instead of steel—can create an entirely new consumer product category.
What does this patent NOT cover?
Does not cover cutting tools that use rigid metal blades or discs.
Same assignee
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