Piercing Saw
Piercing Saw
The fine-toothed jeweller's hand saw used for intricate cutting in sheet metal
The piercing saw is the small, light, finely toothed hand saw a jeweller uses for any cut more delicate than a bench shears can manage. The frame holds a replaceable blade under tension between two thumbscrews, and the blade itself is thinner than a millimetre, with anywhere from twenty to nearly ninety teeth per inch. The saw is the working bench's primary tool for cutting curves in sheet, opening interior windows for ajouré work, and shaping the kinds of complex outlines no other tool will produce. Without one, a jeweller is back to files and shears; with one, almost any flat-sheet shape becomes possible.
Frame and blade
The frame is typically a U-shape of light steel or aluminium with two clamping heads, a depth of throat ranging from about two and a half to six inches, and a wooden or moulded handle. Adjustable frames let the user shorten the blade run when blades break — which they do, regularly — recovering the unbroken segment for further work. The blade is held vertically, teeth pointing toward the handle so the cutting stroke is the down stroke. Tension is everything: an under-tensioned blade flexes, drifts, and snaps, and the standard test is a clean, high-pitched ping when the blade is plucked. A dull thud means the blade is loose and the frame needs another quarter-turn.
Blade sizing
Blades are sized on a standard scale that runs from 8/0 (the finest) through 6 (the coarsest), with the smaller numbers carrying finer teeth and thinner kerf. The general rule of thumb is that three teeth should always be in contact with the metal during the cut. For sheet metal between 0.3 and 0.8 millimetres thick, a 4/0 to 1/0 blade is usually appropriate; for thicker stock up to 1.5 millimetres, a size 1 to 3 blade carries the load; for very fine work in thin sheet, sizes 6/0 or 8/0 give the precision needed without ploughing too wide a kerf. Selecting the wrong size is the most common cause of poor cuts: too coarse a blade tears thin sheet, too fine a blade clogs and snaps in thick stock.
Technique
The blade orientation is vertical and the work moves around the blade rather than the blade moving around the work. The user supports the sheet on a bench pin — a wooden V-cut pin clamped to the bench — and holds the saw with the handle below the work, drawing through with rhythmic strokes that use the full length of the blade. Excessive downward pressure breaks blades; a steady, even stroke does the cutting almost without effort. Wax or saw lubricant on the blade extends life and reduces clogging, particularly when cutting silver or copper sheet. Tight curves and inside corners are managed by sawing on the spot — running the saw without forward motion until the kerf is wide enough to turn the blade.
Pierced and ajouré work
The piercing saw earns its name from interior cutting: drilling a small hole, threading the blade through, retensioning, and sawing out an internal window. Ajouré, fretwork, openwork brooch panels, and the pierced backplates of Edwardian and Art Deco jewellery all rely on this technique. Each interior cut is a small operation in itself, with the blade threaded, retensioned, and re-released as the work progresses. A complex panel with a dozen interior cuts is a meditative half-hour at the bench; the discipline rewards patience and a steady hand.
In the trade
The piercing saw is one of the small handful of tools every jeweller owns from the first day at the bench. New blades are bought by the dozen or by the gross — typical breakage rates run one to three blades per session of focused work, and a hobbyist's two-dollar pack of blades is a production shop's morning consumable. The frame itself is far more durable; a good adjustable frame will see decades of use with nothing more than the occasional replacement of a clamping screw. The piercing saw is unglamorous equipment, but the work it makes possible is most of what separates fabricated jewellery from cast.