Reamer — The Bench Tool for Sizing Drilled Holes
Reamer — The Bench Tool for Sizing Drilled Holes
A tapered hand tool for enlarging or smoothing the drilled holes in pearls, beads, and gemstones
A reamer is a tapered hand tool used by jewellers, lapidaries, and pearl stringers to enlarge, smooth, or true the drilled holes in beads, pearls, and gemstones. The tool is rotated manually or in a pin vice, and the tapered cutting surface progressively widens the hole as it is inserted. Reamers are typically made of hardened steel, diamond-coated steel, or — for the most demanding applications — solid carbide. The choice of material depends on the hardness of the host gem material and the precision required of the final hole.
Why reaming is needed
Drilled holes in pearls, beads, and gemstones rarely emerge from the drilling operation in finished form. Drill bits chip slightly at exit, leave rough internal surfaces, and produce holes whose diameter varies along the length. For stringing or setting, the hole must be smooth, of consistent diameter, and sized precisely to the thread, wire, or post that will pass through it. The reamer accomplishes the smoothing and sizing in a single operation, gradually working the hole to specification without the brute-force material removal of a fresh drill.
Reaming is most commonly performed on pearls — where the drilled hole must accommodate silk thread for stringing — and on hardstone beads, where wire or cord passes through. The technique extends to faceted gemstones in some applications, particularly for top-drilled briolettes, dangling beads, and other configurations where a precise, smooth hole is essential.
Tool materials and selection
Hardened-steel reamers are the standard tool for pearls and softer gemstones. The material is sufficiently hard to cut nacre, calcite, opal, and similar species without significant tool wear, and the price is modest. Diamond-coated reamers are used on harder species — including chalcedony, jasper, agate, and the corundum and beryl family — where steel cuts too slowly or wears too quickly. Solid carbide reamers, the most expensive option, are used in production settings and on the hardest gem materials.
Reamer selection also depends on the hole geometry. Standard reamers have a long taper that progressively widens the hole; bullet-tip reamers have a more aggressive cutting tip for opening tight holes; ball-end reamers are used for smoothing the entry and exit chamfers without altering the through-hole diameter. Pin vices and tool handles permit the cutter to apply controlled rotation and pressure.
Technique
Reaming is performed slowly, with the cutter feeling the resistance of the material and avoiding excessive force that would crack the host gem. For pearls, the reamer is typically inserted from one side, rotated gently while applying light pressure, and withdrawn periodically to clear chips. The same operation is performed from the other side to taper the hole evenly. For harder gem materials, water lubrication or oil is sometimes used to reduce friction and clear chips, particularly with diamond-coated reamers.
The principal failure mode is cracking the host material. Pearls in particular are vulnerable: the nacre layer can fracture along the drill axis if reaming is too aggressive, particularly in cultured pearls with thin nacre over the bead nucleus. Experienced reamers work to a feel that is acquired through practice, and the conservative approach — multiple light passes rather than a single aggressive operation — is the standard in good practice.
In the trade
Reaming is a routine bench operation in pearl-stringing, bead-restoration, and bead-setting work. Pearl restringers ream pearls during routine maintenance to address worn drill holes; bead jewellers ream commercial bead inventory to fit specific thread or wire diameters; lapidary studios producing custom pieces ream finished stones to integration specifications. The tool is inexpensive, the technique is acquired through practice, and the operation is part of the everyday vocabulary of fine bench work. Specialist suppliers including Otto Frei, Rio Grande, and Stuller provide reamers in the range of materials and geometries the trade requires.