Quill Stop — The Limit Device That Protects Stones on the Faceting Machine
Quill Stop — The Limit Device That Protects Stones on the Faceting Machine
A mechanical or electronic limit on quill travel that sets repeatable cutting depths and prevents over-cut
A quill stop is the mechanical or electronic limit on a faceting machine that restricts how far the quill — and with it the dop and stone — can travel toward the lap. In commercial and amateur faceting alike the stop is the safety net between the cutter and the irreversible: a moment's inattention with no stop in place will round off a fragile keel, undercut a critical girdle, or grind through into the dop itself.
Function in the cut
The quill is the spindle assembly that holds the dop arm and rotates the stone against the lap. On most modern faceting machines the cutter sets the stop to a precise depth corresponding to the design specification — a calculated pavilion main angle and a specific girdle width, for example — and the machine refuses further travel beyond that point. The cutter can then rotate the indexing wheel through every facet position at the same angle without re-measuring depth, producing a cleanly meeting set of facets at exact specification.
For step-cut and emerald-cut work the stop is essential: long, parallel facets must terminate at exactly equal heights, and a few thousandths of an inch of variation is visible to the naked eye in the keel-line meet. For brilliant cuts the stop ensures the pavilion mains all meet at the culet without one facet running deeper than its neighbours.
Mechanical and electronic implementations
Older and simpler machines use a threaded screw with a locking collar; the cutter advances the collar to the desired depth and the quill bottoms out against it. Higher-grade machines use a calibrated micrometer barrel with vernier markings allowing depth adjustments in the order of 0.001 inch. A small number of high-end faceting machines, particularly those used in production environments, incorporate electronic limit switches that stop the quill drive when a set position is reached.
The quill stop should be distinguished from the spindle lock — a separate mechanism that immobilises the quill rotationally for dop changes, transfer, or maintenance. Some manufacturers use the term quill stop for both functions; others reserve it strictly for the depth-limit device.
Care and calibration
Stops on production machines accumulate wear and contamination from cutting slurry and require periodic calibration against a master gauge. A stop that has drifted by a few thousandths will produce facets that do not meet correctly, and the cutter who relies on the indicated depth without verifying against actual cut will produce systematically defective work.