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Lapidary terms

Machine listings use unfamiliar words for ordinary parts and steps. For example, a wheel's "bore" is its centre hole. Use these definitions while choosing equipment or cutting a first stone.

Stone and shape

A cut slab, a domed cabochon with a flat back, and a stone held on a dop stick. — **Three common stone-cutting terms** 1 Slab and saw kerf2 Cabochon3 Stone on a dop The drawings show shapes and tools, not a required size or setting.

Lapidary: The work of cutting, shaping and polishing stone, or a person who does that work. Cabbing, faceting and carving are different lapidary methods. See how the cuts differ.
Rough: Stone before it has been cut into its intended shape. A cutter may saw one piece of rough into several slabs.
Slab: A relatively flat slice cut from rough. A cutter marks an outline on a slab, then trims away the excess before shaping the dome. CabKing shows that sequence.
Cabochon, or cab: A stone shaped with a smooth, rounded face rather than a set of flat facets. A simple cab usually has a flat back; it need not be oval. GIA defines simple and double cabochons.
Cabbing: Making a cabochon: choosing the stone, cutting it into a rough shape called a blank, smoothing it, then polishing it. A cabbing machine handles much of the shaping and smoothing; a saw or flat disc may do other steps. Follow one stone through the work.
Dome: The rounded upper surface of a cabochon. Its curve should continue smoothly to the edge. See the form and section drawing.
Double cab: A cabochon with two rounded faces instead of a rounded face and flat back. It needs a different setting or display plan from a simple cab. GIA describes both forms.
Mohs hardness: A ranking from 1 to 10 of how easily one mineral scratches another, from talc at 1 to diamond at 10. The steps are not equal, so the numbers give an order rather than an amount. Quartz, which includes agate and jasper, rates 7. A hard stone can still chip or split: hardness is not toughness. GIA explains the scale and its limits; GIA on agate and jasper; choose a first stone.
Preform: A roughly shaped stone that has its intended outline but has not reached its final surface or polish. "Preforming" names that early shaping step; it does not mean the stone is ready to set. GIA's Gems & Gemology, Winter 2004, page 291, on preforming.

Cutting and holding

Trim saw: A saw for cutting a small blank from a slab or removing material around a marked shape. Its blade makes straight cuts; the grinding wheel makes the curves. Compare trim and slab saws.
Slab saw: A saw built to make slices from larger rough, often with a vise and a controlled feed. Names overlap at smaller blade sizes, so check the actual cutting clearance and workholding. See the saw guide.
Kerf: The width of material a blade removes as it cuts. For a diamond saw, the cutting rim can be wider than the blade's inner core. A thinner kerf wastes less stone, but the blade must suit the saw and the work. Hi-Tech explains core and kerf; check blade fit.
Dop, dopping: A dop is a handle attached to a small stone; dopping means attaching it, often with wax. The handle keeps fingers away from the wheel and helps control a small cab. CabKing shows when it uses a dop; see finishing supplies.
Cab rest: A support in front of the wheels for steadying your hand or a dop stick. Diamond Pacific includes one with its Gem Makers; MK Diamond calls the part on its GP-6 a tool rest, and CabKing supplies hand rests. Diamond Pacific 2020 catalogue; MK GP-6 manual.

Machines and fit

Cabber: Short for cabbing machine: a motor-driven set of grinding and sanding wheels, usually supplied with water. Some machines include a polishing station; others need a separate pad or lap. See the machine parts.
Arbor: The metal shaft that carries a wheel, drum or flat disc, sometimes sold with its supports. A bare arbor may omit the motor and water system. Read the listing before assuming it is a complete machine. Compare complete units and open arbors.
Bore, or arbor hole: The centre hole in a wheel or lap that fits over its shaft. Measure the hole and shaft together; the size in "six-inch wheel" is the outside diameter, not the bore. CabKing specifies a one-inch arbor hole for its wheels.
Bushing: A sleeve that fits inside a wheel's bore so the wheel fits a smaller shaft. CabKing supplies its one-inch-bore wheels with bushings for ½-, ⅝- and ¾-inch arbors. Diamond Pacific's six-inch Galaxy wheels take one bushing; its six-inch Nova wheels take two. Use the arrangement the wheel and machine makers specify. CabKing wheel listing; Diamond Pacific 2020 catalogue, page 10.
Spacer: A short collar that sits on the shaft between wheels and sets the gap between them. A wider or narrower replacement wheel can change the spacers needed. CabKing's six-inch manual sets a gap of about ¾ inch between wheels. CabKing 6V3 manual; Diamond Pacific spacers.
Runout: How far a turning wheel strays from a true circle: a rim that rises and falls, or a side that wobbles. MK Diamond makes its brazed GP-6 wheels to a low runout to prevent pounding during grinding. Watch each wheel turn before buying a used machine. MK GP-6 manual.
Expanding drum: A rubber drum that holds an abrasive belt. The drum expands as it turns, gripping the belt; the belt supplies the working grit. Measure drum diameter, belt width and bore before ordering. Covington explains the expansion slots.
Lap, flat lap: A lap is the flat disc or plate used to grind or polish a flat surface. "Flat lap" can also name the machine that moves it. A rotating disc and a vibrating pan use different abrasives. See the two machine types.

Abrasives and finish

Grit: The abrasive grade printed on a wheel, belt or disc. Lower numbers usually cut faster and leave deeper scratches; higher numbers use finer particles for smoothing. An 80-grit wheel and a 3,000-grit wheel do different jobs. CabKing explains its wheel sequence.
Mesh, micron: Other labels for abrasive size, common on polishing compounds. A micron is a unit of particle size, so a smaller micron number means finer particles; a higher mesh number means finer particles, as with grit. Diamond Pacific grades its diamond compound by mesh, and MK Diamond grades its GP-6 polishing compounds in microns. Makers' labels may not convert exactly, so follow the sequence for the abrasive system you use. Diamond Pacific compound; MK GP-6 manual, parts list; see polishing compounds.
Plated, sintered and resin-bond: These words name how an abrasive holds its diamond. A plated, or electroplated, wheel holds diamond in a hard nickel layer on its surface, for grinding and early shaping. A sintered blade or wheel holds diamond through the depth of a metal rim; stone packed into the metal can dull it until the rim is dressed. A resin-bond wheel holds diamond in a more yielding layer for later smoothing. The bond matters as well as the grit number. CabKing's plated wheels; Diamond Pacific 2020 catalogue, page 10; Hi-Tech on sintered blades; compare wheel families.
Dressing: Touching an abrasive stick to a turning wheel or blade to clear a clogged or glazed face and expose fresh abrasive. Whether a wheel needs it depends on how it is made. Diamond Pacific says its plated Galaxy wheels never need dressing. MK Diamond dresses its brazed GP-6 wheels with a green carbide stick for no more than 2 to 3 seconds under full water, and warns that over-dressing shortens wheel life. Hi-Tech dresses its sintered saw blades but advises against dressing its notched-rim or electroplated blades. Follow the maker's instructions for each wheel or blade. Diamond Pacific 2020 catalogue, page 10; MK GP-6 manual; Hi-Tech FAQ.
Slurry: A wet mixture of abrasive or stone particles. A vibrating flat lap needs a controlled loose-grit slurry in its pan; a cabber's tray instead collects the water and material washed from its wheels. Covington gives the vibrating-lap method.
Polish: The final finishing stage, done with a suitable pad or lap and compound once the coarser scratches have gone. More polishing compound will not remove a deep grinding mark. Choose a pad and inspect the surface.