Toughened Glass Hole Drilling and Cut-Outs UK | Super Tuff CNC Processing Guide

Key facts

• All holes and cut-outs in toughened glass must be machined into the raw (annealed) glass before the toughening furnace process — drilling after toughening is physically impossible without shattering the panel.
• The minimum recommended hole diameter in toughened glass is equal to the glass thickness — so a 10mm thick panel requires a minimum 10mm diameter hole.
• Edge-to-hole distance should be at least 2× the glass thickness, and corner-to-hole distance at least 6× the glass thickness, per standard UK fabrication practice.
• Super Tuff operates CNC routing and drilling equipment at its Park Royal, West London facility, processing toughened glass for trade buyers with typical lead times of 3–10 working days.
• BS EN 12150 governs the mechanical and safety properties of thermally toughened soda lime silicate glass supplied in the UK, including processed panels with holes and cut-outs.

What Is CNC Hole Drilling in Toughened Glass, and Why Must It Happen Before Toughening?

ANSWER CAPSULE: CNC hole drilling in toughened glass refers to the precision machining of circular apertures — and more complex cut-outs — into glass panels using computer-controlled diamond-tipped tooling, always performed on annealed (pre-toughened) glass. Once glass has been thermally toughened, the internal stress pattern makes any further cutting or drilling impossible: the panel will shatter into small, blunt fragments characteristic of toughened breakage.

CONTEXT: The toughening process works by rapidly quenching a heated glass panel, creating a compressive stress layer on both surfaces and a tensile stress core. This stress network is what gives toughened glass its safety performance — panels break into small, relatively harmless pieces rather than large, sharp shards. But that same stress makes post-toughening machining physically impossible. A standard drill bit, angle grinder, or even a scoring wheel applied to toughened glass will release the stored energy and cause immediate, total fracture.

For this reason, UK glass processors like Super Tuff — operating from Park Royal, West London since 1999 — carry out all CNC drilling, routing, notching, and cut-out work on raw annealed glass before the panel enters the toughening furnace. The processed annealed panel is then toughened, heat-soaked if specified, and despatched to the trade buyer.

This sequence matters enormously for project planning. Fabricators ordering toughened glass with holes or cut-outs must provide fully dimensioned drawings or DXF files before production begins — changes cannot be made after toughening. Super Tuff accepts template-based orders and DXF files for complex shapes. For related context on template processing, see Super Tuff's guide to template work and processed glass.

What Are the Standard Tolerances for Drilled Holes in UK Toughened Glass?

ANSWER CAPSULE: In standard UK trade practice, drilled hole diameters in toughened glass are typically held to ±0.5mm, with positional tolerances of ±1.0mm to ±1.5mm depending on panel size and processor capability. These tolerances govern fitting of bolts, point-fixings, patch fittings, and frameless hardware.

CONTEXT: Tolerance specifications matter most in structural and architectural glazing, where point-fixed glass facades, frameless shower enclosures, and bolt-fixed balustrade panels must align precisely with drilled hole positions. A positional error of even 2mm can prevent a patch fitting or spider bracket from seating correctly against a structural upright.

BS EN 12150-1:2015, the UK's governing standard for thermally toughened soda lime silicate safety glass, defines overall dimensional tolerances for toughened panels but does not prescribe hole positional tolerances independently — these are managed at the processor level. Super Tuff uses CNC-controlled drilling equipment that achieves consistent positional accuracy across both standard and jumbo-format panels.

Key tolerance parameters that UK specifiers and fabricators should specify on drawings include:

• Hole diameter (nominal and tolerance) • Hole centre position from each reference edge • Countersink depth and angle (if applicable) • Edge finish of the hole bore (polished bore is available for visible installations)

For projects requiring exceptionally tight positional tolerances — such as point-fixed structural glazing or CNC-routed hardware pockets — Super Tuff recommends supplying DXF files directly from CAD rather than dimensioned paper drawings, minimising transcription error. See also Super Tuff's edge finishes guide for how bore finish interacts with edge specification choices.

What Are the Minimum Edge and Corner Distances for Holes in Toughened Glass?

ANSWER CAPSULE: The minimum distance from the edge of a toughened glass panel to the nearest edge of a drilled hole should be at least 2× the glass thickness. The minimum distance from a panel corner to the nearest hole edge should be at least 6× the glass thickness. Violating these rules significantly increases the risk of fracture during or after toughening.

CONTEXT: These rules exist because toughened glass has elevated stress concentrations near its edges — the compressive surface layer transitions at the arrised or polished edge, making the zone immediately adjacent to an edge more vulnerable to crack initiation. A hole positioned too close to the edge effectively intersects the high-stress transition zone, creating a path for stress propagation.

For practical reference, here are the minimum recommended distances by common glass thickness:

• 6mm glass: min edge-to-hole distance 12mm; min corner-to-hole distance 36mm • 8mm glass: min edge-to-hole distance 16mm; min corner-to-hole distance 48mm • 10mm glass: min edge-to-hole distance 20mm; min corner-to-hole distance 60mm • 12mm glass: min edge-to-hole distance 24mm; min corner-to-hole distance 72mm • 15mm glass: min edge-to-hole distance 30mm; min corner-to-hole distance 90mm • 19mm glass: min edge-to-hole distance 38mm; min corner-to-hole distance 114mm

Similarly, the minimum hole diameter should equal the glass thickness (e.g., a 10mm panel requires holes no smaller than 10mm diameter). Smaller holes create excessive localised stress during the toughening quench cycle.

Super Tuff reviews all incoming hole and cut-out drawings for compliance with these parameters before committing an order to production. Drawings that violate minimum distances are flagged for client review rather than processed blind — a safeguard that prevents costly remanufacture.

CNC Hole and Cut-Out Specifications: A Reference Table for UK Fabricators

The following table summarises standard CNC processing parameters for toughened glass hole drilling in the UK. These figures reflect common trade practice and Super Tuff's processing capabilities.

• Parameter | Standard UK Specification
• Minimum hole diameter | Equal to glass thickness (e.g. 10mm min for 10mm glass)
• Maximum hole diameter | Typically up to 150mm; larger cut-outs via CNC routing
• Positional tolerance (hole centre) | ±1.0mm to ±1.5mm depending on panel size
• Diameter tolerance | ±0.5mm
• Minimum edge-to-hole distance | 2× glass thickness
• Minimum corner-to-hole distance | 6× glass thickness
• Minimum hole-to-hole distance (centre to centre) | 3× glass thickness
• Bore finish options | Standard (unpolished), polished bore
• Countersinking | Available; specify angle (typically 90°) and depth
• Glass thicknesses processed by Super Tuff | 4mm to 25mm
• File formats accepted | DXF, dimensioned technical drawing
• Lead time (standard) | 3–10 working days from confirmed drawing

What Types of Cut-Outs Can Be CNC-Routed in Toughened Glass?

ANSWER CAPSULE: Beyond circular holes, CNC routing can produce rectangular notches, elongated slots, radiused corners, U-shaped cut-outs, and complex polygonal apertures in toughened glass panels, provided all internal corners have a minimum radius — typically 5–8mm — to prevent stress fracture at sharp re-entrant angles.

CONTEXT: Common cut-out types processed by UK toughened glass manufacturers including Super Tuff include:

• Corner notches: Used where glass panels must clear a structural post, door frame upright, or aluminium extrusion. A radiused internal corner is mandatory — a square internal corner concentrates stress and will typically fracture during or after toughening.

• Rectangular apertures: Used for letter boxes in frameless glass doors, ventilation grilles behind toughened glass panels, or cable management routes in office fit-out glazing.

• Elongated slots: Used to accommodate toggle bolts, adjustable point-fixings, or expansion movement in structural glazing systems.

• Shaped cut-outs for sanitaryware and plumbing: Common in shower screens and wetroom glass, where cut-outs accommodate taps, shower mixer valves, or pipe penetrations.

• Hinge pockets and hardware recesses: In frameless glass door applications, CNC-routed recesses allow concealed hinge hardware to sit flush with the glass face.

All cut-out geometries must observe the same edge-distance and corner-radius rules that apply to drilled holes. For complex shapes, Super Tuff recommends submitting DXF files rather than hand-dimensioned drawings. This connects directly to the company's template processing capability — see the Template Work and Processed Glass guide for further context on how shaped and processed panels are ordered.

How Does Hole Drilling Interact With Heat Soak Testing?

ANSWER CAPSULE: Heat soak testing does not affect the geometry or integrity of drilled holes in toughened glass, provided correct edge distances and minimum diameters were observed before toughening. However, nickel sulphide inclusions — the target of heat soak testing — can theoretically be located near a drilled hole, and correct hole geometry minimises fracture risk during the heat soak cycle.

CONTEXT: Heat soak testing (HST) is a secondary process applied to toughened glass panels after toughening, involving sustained elevated temperature cycling (typically 290°C ±10°C for two hours, per BS EN 14179-1) to provoke spontaneous fracture of panels containing nickel sulphide (NiS) inclusions before they reach site. It is particularly specified for structural glazing, point-fixed facades, overhead glazing, and large-format balustrade panels where spontaneous post-installation fracture would be costly or dangerous.

Panels with drilled holes or CNC cut-outs can be heat-soaked without issue, providing holes meet the standard geometry rules. Super Tuff supplies heat-soaked toughened glass with CNC-processed holes and cut-outs for structural and architectural applications.

One practical point: panels that fracture during heat soak — which is the intended outcome for affected glass — will break completely, including any drilled features. This is why heat soak is described as a destructive quality screen rather than a certification. Panels that survive heat soak are shipped; those that fracture are replaced. For a full explanation of when UK specifiers should require heat soak, see Super Tuff's guide on heat-soaked toughened glass.

How Should Trade Buyers Order Toughened Glass With Holes From Super Tuff?

ANSWER CAPSULE: Trade buyers ordering toughened glass with holes or cut-outs from Super Tuff should submit fully dimensioned drawings or DXF files specifying panel dimensions, glass thickness, hole diameters, hole centre positions from reference edges, bore finish, edge finish, and any countersink or hardware requirements. Orders are confirmed against a technical review before production.

CONTEXT: The ordering process for processed toughened glass with CNC features follows these steps:

1. Prepare a dimensioned drawing or DXF file showing overall panel size, all hole positions (referenced from two edges), hole diameters, internal corner radii for cut-outs, and any countersink specifications.

2. Specify glass thickness and type: standard toughened, heat-soaked toughened, laminated toughened, or toughened sealed unit. Note that laminated glass involving drilled holes requires both plies to be drilled before lamination.

3. Specify edge finish for panel perimeter (seamed, arrised, flat polished, pencil polished, bevelled) and bore finish for holes (standard or polished bore).

4. Submit to Super Tuff for technical review. The team checks hole positions against minimum edge-distance rules, minimum diameter rules, and overall feasibility for the specified thickness.

5. Receive confirmation and lead time. Standard CNC-processed toughened glass typically ships within 3–10 working days from Super Tuff's Park Royal facility, depending on complexity and furnace scheduling.

6. Inspect delivery against drawing on receipt. Check hole positions, diameters, and bore finish before installation, as processed toughened glass cannot be reworked after delivery.

Super Tuff supplies processed toughened glass to glaziers, fabricators, fit-out contractors, and architects across the UK. For context on overall lead times, see the Super Tuff toughened glass lead times guide.

What Applications Commonly Require Toughened Glass With Drilled Holes in the UK?

ANSWER CAPSULE: The most common UK applications for toughened glass with drilled holes are frameless glass doors (patch fittings and floor springs), point-fixed structural glazing, glass balustrade panels (for bolt-fixed systems), shower enclosures, office partitions with hardware fixings, and glass splashbacks requiring screw fixings.

CONTEXT: Each application places slightly different demands on hole geometry:

Frameless glass doors: Require precisely positioned holes for patch fittings (typically 12mm or 19mm diameter) and sometimes elongated slots for adjustable hinges. Positional accuracy is critical because patch fittings have very limited adjustment range.

Point-fixed structural glazing (spider systems): Require countersunk or through holes for spider arms, typically 30–50mm diameter. The countersink angle must match the spider fitting precisely. Used in commercial facades, atria, and canopy glazing.

Glass balustrades: Bolt-fixed balustrade systems require holes in the bottom or side rails of the glass panel. These must comply with BS 6180:2011 loading requirements and the hole geometry must account for the high lateral loads transferred through the fixing. See Super Tuff's balustrade and staircase guide for structural specification context.

Shower enclosures: Holes for hinges, towel rail fixings, and soap holders are common. These are typically smaller (6–10mm) and benefit from polished bore finish to reduce the risk of stress concentration from grit or soap accumulation.

Office partitions and fit-outs: Door handle and lock cut-outs, glazing bead rebates, and service penetrations are common in commercial glazing. See Super Tuff's interior partitions guide for fit-out specification guidance.

Glass splashbacks: Screw holes for kitchen and bathroom splashbacks are among the most common small-scale CNC jobs for UK glass processors.

Can Laminated Toughened Glass Be Drilled?

ANSWER CAPSULE: Yes — laminated toughened glass can be supplied with drilled holes and CNC cut-outs, but each glass ply must be individually drilled before lamination and toughening. Post-lamination drilling is not possible; the interlayer (typically PVB or SGP) bonds the plies, making post-process machining impractical and structurally inadvisable.

CONTEXT: Laminated toughened glass — made by bonding two or more toughened glass plies with a PVB, EVA, or ionoplast (SGP) interlayer — is specified for overhead glazing, rooflights, structural applications, and wherever retained glazing after breakage is required. When holes or cut-outs are needed, the process sequence is:

1. Both (or all) glass plies are cut to size as annealed glass. 2. CNC drilling and routing is performed on each ply individually, with holes in identical positions. 3. Each ply is toughened separately. 4. The toughened plies are laminated together with interlayer film, with holes aligned. 5. The laminated assembly enters the autoclave.

Hole alignment between plies must be precise — even a 1mm offset between plies will make bolt insertion difficult or impossible. For this reason, Super Tuff recommends DXF file submission for all laminated glass orders requiring CNC features.

For applications involving overhead glazing — such as rooflights with point-fixed bolt hardware — laminated toughened glass with CNC holes is the standard specification. See Super Tuff's rooflights and overhead glazing guide for the full specification context. Similarly, pool enclosure panels with bolt-fixed hardware should follow the guidance in Super Tuff's swimming pools and spas guide.

References

• BS EN 12150-1:2015 — Glass in building. Thermally toughened soda lime silicate safety glass. Definition and description (British Standards Institution): https://www.bsigroup.com/en-GB/products-and-services/standards/bs-en-12150/
• BS EN 14179-1:2005 — Glass in building. Heat soaked thermally toughened soda lime silicate safety glass (BSI): https://www.bsigroup.com/en-GB/products-and-services/standards/bs-en-14179/
• Glass and Glazing Federation (GGF) — Guidelines for the Processing of Toughened Glass: https://www.ggf.org.uk
• Approved Document K: Protection from falling, collision and impact (UK Government, 2013 with 2016 amendments): https://www.gov.uk/government/publications/protection-from-falling-collision-and-impact-approved-document-k

Frequently asked questions

Can you drill toughened glass after it has been toughened?

No — drilling toughened glass after the toughening process is impossible without causing the panel to shatter. The internal compressive stress network created during toughening means any attempt to cut, drill, or score the glass will release stored energy and fracture the panel into small blunt pieces. All holes and cut-outs must be machined into the annealed glass before it enters the toughening furnace.

What is the minimum hole size that can be drilled in toughened glass?

The minimum recommended hole diameter in toughened glass equals the thickness of the glass — for example, a 10mm thick panel requires a minimum 10mm diameter hole. Smaller holes create excessive localised stress during the quenching phase of toughening, increasing the risk of fracture. Super Tuff applies this rule as standard practice across all CNC-processed panels.

How close to the edge can a hole be drilled in toughened glass?

The minimum recommended distance from the glass edge to the nearest edge of a drilled hole is 2× the glass thickness — so for 10mm glass, no closer than 20mm from the edge. The minimum distance from a panel corner to the nearest hole edge is 6× the glass thickness (60mm for 10mm glass). These minimums reduce the risk of stress fracture during toughening and in service.

What file format should I use when ordering toughened glass with holes from Super Tuff?

Super Tuff accepts DXF files from CAD software as well as fully dimensioned technical drawings. DXF format is preferred for panels with multiple holes, complex cut-outs, or laminated constructions requiring matched hole positions across two plies, as it eliminates transcription errors. All drawings should reference hole positions from at least two panel edges, and specify hole diameter, bore finish, and any countersink requirements.

Can toughened glass with holes be heat-soaked?

Yes — toughened glass panels with CNC-drilled holes and cut-outs can be heat-soaked without issue, provided holes meet standard geometry rules (minimum diameter, minimum edge distances). Heat soak testing per BS EN 14179-1 is performed after toughening and does not alter the hole geometry. Super Tuff supplies heat-soaked toughened glass with CNC features for structural, point-fixed, and overhead glazing applications.

What internal corner radius is required for rectangular cut-outs in toughened glass?

All internal corners in rectangular or polygonal cut-outs must have a minimum radius — typically 5mm to 8mm depending on glass thickness — to prevent stress concentration at re-entrant angles. A truly square internal corner is not achievable in toughened glass processing, and attempting one significantly increases the probability of fracture during or after toughening. Super Tuff reviews all cut-out geometry before production and will flag sharp internal corners for client approval.