Evolution of the knuckle lever-cap (i)

The Stanley No.18 is one of those beautiful block planes, partially due to the polished knuckle-joint lever cap. The history of the knuckle lever-cap dates back to Patent No.355,031 issued in 1886. Invented by Samuel D. Sargent, for the Stanley Rule and Level Company, the patent was issued for improvements in “…the manner of holding the cutter bit within the stock”. More specifically, the patent was for a lever cap which can be “clamped by fewer and more direct motions“.

What Stanley proceeded to do was put the lever cap on the No.9½, and the No.15, effectively producing the No.18, and 19 planes. These planes then first appeared in the catalog of 1888. The planes had the requisite “excelsior” style rear-biased cheek.

The first version of the lever cap was comprised of two parts. The upper portion, or clamping lever,  was designed to sit in the palm of the hand, and has a two-pronged fork-like connector near the “knuckle” joint which engages the “headed screw” projecting from a threaded hole in the plane stock. Engaging the screw and pushing down on the knuckle would engage the lower portion of the lever cap, or “holding cap” (wedge). The clamping lever is connected to the holding cap by means of a pintle. When the clamping lever is depressed, the lever fulcrums on the underside of the screw head, and presses the holding-cap down upon the blade.

However, this design is severely flawed in that it usually does not engage effectively, and if the screw is not adjusted properly, can pop open.  If treated harshly, the prongs can also break off. These caps generally have the patent date “PAT. DEC.28.86” embossed on the lower portion of the lever cap. The knuckle lever was replaced with a four-piece lever cap that slips over the lever cap retaining screw, and the “spoon” portion of the lever cap then places pressure on the blade when it is snapped into place. A comparison of the two lever caps is shown below.

The original knuckle lever cap versus the redesigned version.


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