Dop sticks
A dop is a short rod to which a gemstone preform is adhered for cutting. Dops connect the stone to the quill of the faceting machine; the quill then provides the angle and rotational control via the mast and index wheel.
Dops are produced in three principal materials: brass, aluminum, and stainless steel. Each has a distinct thermal profile that affects choice of adhesive. Brass conducts heat at a rate well-matched to traditional dop wax; aluminum is lighter and rapidly transmits temperature changes; stainless steel is preferred where corrosion is a concern, particularly when working with sulfide-bearing material.
End geometries
Common end geometries include:
- Flat — table dops; the stone is mounted with one large planar facet down.
- 45° cone — used during pavilion cutting where the dop face matches an early pavilion break angle.
- 90° cone (V-cone) — for centering rounded preforms.
- V-groove — for rectangular and elongated preforms that require axial alignment.
- Cup — concave face for spherical preforms.
Dop diameters in common use range from 3 mm to 12 mm. Mixed sets typically include 4-, 6-, 8-, and 10-mm dops in each end geometry.
Adhesives
Dop adhesives fall into two broad classes: hot-melt waxes and room-temperature epoxies. Hot-melt waxes are softened on a heated dop, applied to the stone, and allowed to cool. They are removed at low temperature and are reusable.
Room-temperature epoxies are mixed and cured at ambient temperature. They are favored for thermally sensitive species (kunzite, opal, some tourmalines) where wax application could induce stress fractures. Removal typically requires a solvent bath.
Transfer blocks
A transfer block is an alignment fixture that holds two dops in a known geometric relationship, so the stone can be re-mounted between the pavilion and crown stages. Common configurations:
- Two-pin V-groove block — the simplest design; one dop is fixed, the other slides on parallel pins.
- Adjustable-pad transfer block — the receiving cradle is adjustable on multiple axes.
- Indicator-pad block — an indicator surface allows the user to verify alignment at the transfer point.
Transfer-block accuracy is the limiting factor on girdle concentricity in the finished stone. Manufacturers in current production include Ultra Tec, Facetron, Polymetric, Kingsley North, and Imahashi.
Compatibility
The 1/2-inch dop shaft is the de facto standard across North American faceting machines; transfer blocks and quill collets are designed for it. Some Imahashi and Australian machines use metric or proprietary shaft diameters; adaptors are available from the manufacturer.