National Watch Company center wheel and Merritt Burt patent safety pinion
Record status
Individual type · partial
Period
c. 1867–1871
This component assembly consists of a brass center wheel and a steel safety pinion mechanism based on Merritt Burt's 1864 patent design, produced for the National Watch Company.
Built with a threaded center arbor, the arrangement secures a hollow center pinion in place using an adjustable threaded nut. The safety design was intended to allow the nut to unscrew and the pinion to rotate freely if a mainspring broke, absorbing shock and preserving gear teeth. The National Watch Company fitted these assemblies to production movements from approximately 1867 until around 1871, when the design was superseded.
Evidence at a glance
- Linked sources
- 1
- Photograph views
- 1
- Catalogue references
- 0
Counts describe this entry’s documentation, not authenticity, rarity or completeness. Photographs may show one specimen; check each caption and licence.
Technical characteristics
- Type
- Balance, escapement & train part
- Patentee
- Merritt Burt
- Manufacturer
- National Watch Company (Elgin)
- Place recorded
- United States
- Production era
- c. 1867 to c. 1871
- Maker / attribution
- National Watch Company
- Mechanical construction
- Threaded arbor with securing nut and hollow pinion
Design
- Visible features
- • Macro view showing the toothed steel pinion mounted on the central steel arbor above a spoked brass wheel. • A small polygonal faceted nut is tightened directly against the upper face of the center pinion leaves. • The central arbor extends upward past the nut with a stepped pivot tip.
- Patent Mechanism and Function
- The assembly embodies Merritt Burt's design patented on September 13, 1864, which was created to protect delicate watch parts from the shock resulting from a broken mainspring. Burt's construction utilized a threaded arbor on the center wheel to tighten a nut atop a hollowed center pinion, which would otherwise rotate freely on the shaft. When the nut was substantially tightened, the pinion was secured for regular operation. Upon mainspring rupture, reverse force delivered from the barrel to the center pinion created friction against the nut, unscrewing it immediately and allowing the pinion to rotate freely around the arbor until the force was spent.
- Visual Morphology and Assembly
- The component assembly presents a toothed steel pinion mounted on a central steel arbor positioned above a spoked brass wheel. The central arbor extends upward past the assembly with a stepped pivot tip. A small polygonal faceted nut is tightened directly against the upper face of the center pinion leaves. The source contrasts this ungrooved appearance with later Charles S. Moseley pinions that incorporated visible grooves on top of the leaves.
- Production Era and Design Obsolescence
- Adopted shortly after the National Watch Company was organized, Burt's design was fitted to watches sold from the company's 1867 market debut until approximately 1871. In addition to shock absorption, Burt designed the pinion to slip if wound too tightly, but this balance proved problematic because loose nuts caused slipping while over-tight nuts risked broken pinion teeth. Around 1871, Elgin replaced Burt's configuration with an improved design by Charles S. Moseley. Moseley's modification introduced grooves on top of the pinion leaves to generate greater friction between the nut and the pinion.
Identification
- Source note
- Facts transcribed from the linked source listing or collection record. Attribution and specifications are source-reported and have not been independently authenticated.
Catalogue references
No catalogue numbers recorded. Numbers are only published once transcribed from a verified edition of a standard catalogue — they are never inferred.
Research required
- Research required: The specific parent movement serial number and grade from which this center wheel was removed are not stated.
- Research required: The component is shown detached from its watch movement; presence of an optional spring washer is not indicated on this example.