Look a little closer
See the mechanism
Two wheel contacts do different jobs
Read the diagram
In this top-cut arrangement, a traction wheel grips beneath the rolled rim while a cutting wheel penetrates the lid just inside it. Turning the drive advances the rim past the cutting contact. The cut travels around the lid; a side-cut opener places its cutter differently.
Original local contact schematic, not to scale. Cutter inclination and rolled seam are simplified; the gear train, handles and mounting are omitted. The source describes the conventional top-cut type separately from its own rim-cut invention. No claim of a safe or smooth resulting edge.
Diagram basis: US6058613A: background, conventional first/top-cut type.
The handles establish the cutting contact
Open the handles and the working parts separate enough to accept the can's rim. Bring them together and the wheels grip it. On the top-cut arrangement described in the background of patent US6058613A, the traction wheel contacts the underside of the rim and the cutting edge reaches the lid slightly inward of it.
The handles supply the clamping action needed to hold those contacts together. The turning knob has another task: moving the cut forward. A knob alone would be little help if the traction wheel could slip away from the rim.
The teeth get purchase on the rim
The traction wheel is the small toothed wheel, rather than the sharp circular blade. As it turns against the rim, it advances the can relative to the opener. From the can's point of view, the cutting position travels around the lid.
That is why the tool can keep making a circular cut while the hand repeatedly turns a knob in one place. The can rim supplies the track. Its round outline guides the relative motion, instead of requiring the user to draw a circle freehand through the metal.
A second wheel separates the metal
The cutting wheel has a sharpened edge that penetrates the lid. In the geared top-cut version described by the patent, gears connected to the two wheels mesh, so driving one turns the other in the opposite direction. Their axes are inclined relative to each other; they aren't two flat wheels rolling side by side on a tabletop.
After the cutting position has gone around the can, the lid is separated near its outer edge. This operation leaves cut metal. A conventional top-cut opener should not be confused with a tool advertised to separate a seam while leaving a different edge finish.
Not every rotary opener cuts the same place
Other openers cut into the sidewall or part of the rolled rim. Their wheels can meet the can in a different orientation. Changing the cutting location also changes where the wheels contact the can.
Here, follow the top-cut path: traction beneath the rim, cutting through the lid inside it. A side-cut mechanism meets the wall below the rim; a rim-cut mechanism enters the rolled seam itself. Those different contact positions explain why similar-looking rotary tools can leave different edges behind.
The thing to remember
The handles hold the rim, the traction wheel advances the cut, and the cutting wheel separates the lid. Where those wheels meet the can defines the opener family.
What this example leaves out
This is a simplified geared top-cut mechanism, not the detailed rim-cut invention of US6058613A. Other openers can use different drive and cutter arrangements. Cut can and lid edges may be sharp.
Sources & further reading
Source access dates are listed below. Manufacturer descriptions and patents support the specific constructions described, not every product.
- US6058613A — Can opener ↗
Shun So; US patent publication via Google Patents · Retrieved 2026-10-16 · Top-cut first-type prior-art opener: inclined cutter axis, meshing wheel gears, traction at underside of rim and complete lid penetration radially inside rim; different side/rim-cut types.
Background of the Invention, first three types read; selected top-cut passage web lines74–83. The patent's own detailed invention is rim-cut, so its detailed figures aren't used as a top-cut cutaway. Not all cutters are geared or arranged this way.
