Quill — The Spindle That Drives the Stone in a Faceting Machine
Quill — The Spindle That Drives the Stone in a Faceting Machine
The vertical rotating shaft holding the dop and index gear, mounted on the mast
The quill is the rotating spindle on a faceting machine that holds the dop and index-gear assembly, transmitting rotational motion from a hand-driven or motor-driven drive to the gemstone being cut. The quill is mounted vertically on the machine's mast and can be raised, lowered, and tilted to position the stone against the lap at the precise angle and depth required for each facet. Together with the mast, the index gear, and the dop, the quill defines the geometric registration on which all faceting precision depends.
Construction
The quill is typically a precision-ground steel shaft running in sealed bearings within a cylindrical housing on the mast. The lower end of the quill receives the dop — the cup or rod to which the stone is wax-mounted — and the upper end carries the index gear that allows the operator to advance the stone through specific angular positions for each facet. The quill itself rotates freely under the operator's hand or under a small drive motor, and the stone rotates with it.
Quill bearings are critical for cutting precision. Runout — the lateral wobble of the quill as it rotates — translates directly into facet meet-point errors and degrades polish quality. Premium faceting machines specify quill runout below 0.001 inch (25 micrometres) using sealed ball bearings, angular-contact bearings, or ceramic hybrid bearings; lower-cost machines accept somewhat greater runout but remain functional for general work.
Use during cutting
During cutting, the operator sets the quill height to position the stone just above the rotating lap, sets the mast tilt to the angle specified by the cutting design (typical pavilion angles 41 to 43 degrees, crown angles 35 to 42 degrees, depending on stone material and design), and rotates the quill slowly while applying gentle downward pressure. The combination of stone rotation, lap rotation, and constant angle creates a cleanly cut facet.
Between facets, the operator advances the index gear by the increment specified by the cutting design (typically 4, 6, 8, 12, or 16 index positions for symmetric round-brilliant work; arbitrary positions for fancy designs), then resumes cutting. The quill returns to the same angular position relative to the mast at each facet, preserving symmetry across the stone.
Speed and lap interaction
Quill rotation speeds in faceting work are slow — typically 50 to 300 RPM — far below the speeds used in carving, drilling, or polishing operations. The slow speed allows precise control of stock removal and gives the operator continuous feedback on the cutting action through tactile sensation and audible cues. Faster speeds are sometimes used for initial coarse pre-form work and for polishing on softer laps.
The interaction with lap speed and grit determines stock removal rate. Coarse diamond laps (260 to 600 grit) running at 200 to 400 RPM cut quickly with moderate quill speed; fine polishing laps (8000 to 50,000 grit) require slower quill speeds and lighter pressure to avoid scratching the polished surface.
In the workshop
For Skyjems and any working lapidary studio, the quill is one of the four critical precision components on a faceting machine — alongside the mast, the index gear, and the lap drive — that together determine cutting quality. Periodic inspection of quill runout using a dial indicator, replacement of worn bearings, and protection from contamination are basic maintenance tasks for production lapidary work. See also quill bearing, quill height adjustment, and mast for related entries.