Glass Scoring
Glass scoring runs a hardened wheel across the surface to create a controlled fracture line, then breaks the sheet cleanly along it.
- Part
- Cutting
- Revised
- 2026-08-11
At a glance
- Family
- Mechanical
- Typical tolerances
- ±1/32 in (±0.8 mm) with careful hand or CNC-table work; ±1/16 in (±1.6 mm) is common for architectural glass
- Surface finish
- The broken face is as-fractured and sharp, with a lightly crushed band along the score line; edges are then seamed, ground or polished as specified
- Typical volumes
- 1–100,000+; equally suited to one-off work and automated CNC cutting tables
- Lead time
- Minutes per cut; glass shops typically cut to size same-day
- Materials
- Glass
What it is
Glass scoring cuts flat glass without removing any material. A hardened wheel run across the surface under load creates a shallow median crack, and bending the sheet propagates that crack cleanly through the full thickness. There is no kerf, no dust and no coolant beyond a drop of cutting oil.
It works by hand up to about 1/4 in (6 mm) and to roughly 1/2 in (12 mm) with running pliers or a bench breaker; thicker glass goes to a water jet or a diamond saw. Straight lines and gentle outside curves are practical, but inside corners are impossible — the crack runs where the stress field sends it, not where the drawing wants it.
Two rules govern everything: score once and never re-score the same line, and break promptly after scoring.
How it works
- Wheel selection. A tungsten carbide wheel is chosen by included angle, matched to thickness — shallower angles around 120° for thin glass, more obtuse angles up to about 160° for thick. The wrong angle either fails to open a useful crack or crushes the surface.
- Scoring. The wheel is drawn across the surface in a single steady pass with a light film of cutting oil. A correct score looks like a faint line, not a deep scratch: excessive pressure produces flaking along the score and a ragged break.
- Never re-score. Running the wheel down the same line a second time damages the wheel and cannot deepen the existing crack, because the wheel now rides in a groove instead of loading fresh surface.
- Breaking. The sheet is bent to put the scored face in tension — over a fulcrum, by tapping from underneath, or with running pliers. The median crack propagates through the thickness in an instant.
- Break promptly. A score does not stay sharp. The crack tip blunts over time, and a stale score breaks unpredictably and off-line, so scoring and breaking are treated as one operation.
- Grozing. Shapes that cannot be broken out in one piece are nibbled back with grozing pliers, then ground to the line.
- Edge finishing. A raw broken edge is sharp and full of microcracks, and is the weakest part of the finished piece. Edges are seamed (arrised), ground flat or polished depending on the application, and this step is not optional on anything that will be handled or tempered.
Design guidelines
Straight lines and outside curves only
The break follows the stress field, not the score, once it starts. Gentle convex curves break out reliably; concave curves and inside corners do not. Any shape with an internal corner must be nibbled and ground, or cut by water jet instead.
Minimum strip width
About 0.4 in (10 mm) by hand, narrower with running pliers. Below that the strip breaks up rather than snapping along the score.
Tempered glass cannot be scored at all
Toughened glass is in a balanced state of surface compression and core tension; any penetration of the surface causes the whole pane to disintegrate. All cutting, drilling and edge work must be completed before tempering — a change to a tempered pane means a new pane.
Laminated glass is a two-sided operation
Score and break both glass plies, then part the interlayer with heat or a blade. The edge quality of laminated work is inherently rougher than monolithic glass.
Specify the edge, not just the outline
A raw broken edge is a safety hazard and the main strength limit of the finished piece. State whether the edge should be seamed, ground or polished. Any glass destined for tempering must be edge-worked first, because a flaw at the edge becomes the failure origin.
Score the right face on coated glass
Low-E and other soft coatings are scored from the uncoated side. Confirm coating orientation before cutting, since it also determines which way the pane faces when installed.
| Glass type | Scoring suitability | Notes |
|---|---|---|
| Annealed float glass | Excellent | The standard case; hand or CNC table |
| Low-iron float | Excellent | Same behavior as standard float |
| Coated / low-E glass | Good | Score from the uncoated face |
| Laminated glass | Workable | Score both faces, then part the interlayer |
| Patterned / rolled glass | Fair | Score the smooth face; breaks less predictably |
| Borosilicate | Fair | Harder and less forgiving than soda-lime |
| Wired glass | Poor | Score and break the glass, then cut the wire |
| Tempered / toughened glass | Impossible | Shatters; must be cut before tempering |
| Over 1/2 in (12 mm) thick | Impractical | Use water jet or a diamond saw |
| Feature | Recommended | Limit | Why |
|---|---|---|---|
| Thickness, hand scoring | ≤ 1/4 in (6 mm) | ~1/2 in (12 mm) with a breaker | Crack must run the full thickness |
| Minimum strip width | ≥ 0.75 in (19 mm) | ~0.4 in (10 mm) | Narrow strips break up |
| Curve type | Convex only | Gentle radii | The break follows the stress field |
| Inside corners | Not achievable | Groze and grind, or water jet | Crack cannot turn a corner |
| Time from score to break | Immediate | Minutes | The crack tip blunts with time |
| Edge condition | Seamed or ground | As-broken is sharp | Edge flaws govern strength |
Cost drivers
Scoring itself is nearly free — a wheel, a straightedge and a few seconds. Cost lives in the material, in the edge work and in breakage.
Sheet yield. Glass is bought as full sheets and the offcuts are usually unusable. Sizing parts so they nest into standard stock sheets is the largest single lever on cost.
Edge finishing. Seaming, grinding and polishing are separate operations, and on a small part the polished edge can cost more than the glass. Specify only the edge class the application needs.
Breakage. Scrap from bad breaks, handling damage and chipped corners is a normal part of the process and is priced into the job. Thicker and larger panes carry higher breakage risk.
Thickness. Thicker glass is more expensive per unit area, harder to break cleanly, and past about 1/2 in (12 mm) moves to a different process entirely.
Sequence with tempering. Because tempered glass cannot be cut, every dimensional change means a new pane. Confirm sizes before the tempering step, not after.
Three ways to take cost out:
- Design pane sizes that nest into standard sheet dimensions.
- Specify seamed edges where the glass will be captured in a frame and reserve polished edges for exposed edges.
- Keep all outlines to straight lines and convex curves so the shape can be broken out rather than ground.
Questions
6 questionsHow thick a glass can be cut by scoring?
Up to about 1/4 in (6 mm) by hand and roughly 1/2 in (12 mm) with running pliers or a bench breaker. Above that the crack no longer propagates reliably through the full thickness, and water jet cutting or a diamond saw is the right process.
Why can't tempered glass be cut?
Toughened glass holds its surface in compression balanced against tension in the core. Any penetration of that compressed surface releases the stored energy and the entire pane disintegrates into fragments. All cutting, drilling and edge work must be finished before tempering, so a dimensional change means a new pane rather than a rework.
Why should you never score the same line twice?
The second pass cannot deepen the existing crack because the wheel rides in the groove it already made rather than loading fresh surface, and it damages the wheel. A single steady pass with correct pressure produces a faint line and a clean break; a re-scored line produces flaking and a ragged edge.
How soon after scoring should glass be broken?
Immediately. The tip of the median crack blunts over time, and a score left standing breaks unpredictably and wanders off the line. Production practice treats scoring and breaking as a single operation rather than two separate steps.
Can glass scoring cut inside corners?
No. Once a break starts it follows the stress field rather than the score, so concave curves and internal corners cannot be broken out. Those shapes are nibbled back with grozing pliers and ground to the line, or cut by water jet, which has no such restriction and also produces no heat affected zone.
What tolerance can glass cutting hold?
About ±1/32 in (±0.8 mm) with careful hand work or on a CNC scoring table, and ±1/16 in (±1.6 mm) is commonly accepted for architectural glazing. Because scoring removes no material there is no kerf to compensate, but the break can wander slightly from the score line.