A clean break starts long before the running pliers touch the glass. Four fundamentals decide whether a score line opens into a straight, flake-free edge.
Match wheel angle to thickness
A cutting wheel is not one tool but a family: shallower angles around 135° suit thin float, steeper angles up to 155° drive the median crack deeper into thick stock. Running a thin-glass wheel on 15 mm plate produces a shallow score that wanders on the break — the edge tells you afterwards what the wheel should have been.
Pressure is a window, not a maximum
Too little pressure leaves an interrupted score; too much crushes the surface and throws flakes that become edge chips. The correct window produces a faint, continuous whisper of a line with almost no visible dust. On CNC tables, store the pressure per thickness in the recipe and resist the urge to add force when a wheel starts dulling — change the wheel.
Keep the oil film honest
Cutting fluid does two quiet jobs: it lubricates the wheel bearing and it keeps the fresh median crack from healing before the break. An oil-starved wheel squeals and skips; too much oil floods the score and contaminates downstream washing. A fine, consistent feed — a damp line, not a wet one — is the mark of a well-set head.
Break while the score is fresh
A score line is a wound that starts closing immediately. Break within minutes and the crack runs true along the scored path; leave a scored sheet overnight and the same line breaks reluctantly, with random run-outs. Plan the cutting sequence so scoring and breaking travel together down the table.
