Micro holes in glass are drilled either mechanically, with diamond tools at low speed and constant coolant, or with ultra-short pulse lasers. Mechanical drilling suits prototypes and simple holes. Lasers suit tight tolerances, small diameters and volume. The right choice depends on hole diameter, glass thickness, edge quality, quantity and what the part must survive in service. This guide is for engineers and buyers specifying holes in technical glass. It is not a DIY guide for sea glass or mirrors.
TL;DR
- Specialists call a hole “micro” when it is under 3 mm in diameter.
- Mechanical drilling is cost-effective for prototypes, but it risks micro-cracks and chipping at the hole exit, and it is rarely suitable for high-precision production.
- Ultra-short pulse lasers can produce crack-free, high-aspect-ratio holes with little or no taper, which reduces cleaning and deburring.
- State diameter, tolerance, exit-side chipping limit, glass type and volume on the drawing. These decide the process.
- Dust and mist from glass machining fall under COSHH in the UK, so the process needs a risk assessment.
Table of Contents
- What counts as a micro hole in glass
- The main ways to drill micro holes in glass
- Why the edge of the hole decides the life of the part
- How to specify a micro hole so it can be made and inspected
- Prototype first, then scale
- Health and safety when machining glass in the UK
- Our perspective
- Working with Precision Glasses
- FAQ
- Sources
What counts as a micro hole in glass
Drilling specialists generally use the term micro drilling for holes smaller than three millimetres, according to Sandvik Coromant. In glass, that covers a wide range of real parts:
- sensor windows with vent or alignment holes
- display and touch-screen cover glass with small apertures for microphones, sensors or light pipes
- microfluidic and analytical plates with through-holes for fluid access
- lighting and instrument lenses with mounting or wiring holes
- optical windows with datum holes for assembly
Glass is hard and brittle and has no plastic zone to absorb stress. Every hole is a stress concentrator, so how the hole is made matters as much as where it sits.
The main ways to drill micro holes in glass
Mechanical drilling with diamond tools
The review of micro-hole drilling on glass substrates describes mechanical drilling as an accessible, cost-effective route for small quantities and prototypes. It also sets out the limits. Diamond-coated tools are generally preferred to cemented carbide because of their wear resistance. Speeds must stay low and coolant continuous to prevent thermal stress. Feed rates in the review sit around 5 μm/s, which is slow.
The typical defects are chipping on the exit side and micro-cracks that grow from the hole. Sacrificial backplates and coolant reduce chipping, but they cost throughput and are hard to automate.
If you are working at small scale and want to see what a hand-fed bit can do, a glass-art supplier’s guide to drilling small holes in glass shows the principle with 2.1 mm bits on sheet glass. Industrial parts with a tolerance and an inspection plan are a different job.
Ultra-short pulse laser drilling
Laser micromachining removes material without touching it. In research, picosecond and femtosecond systems have produced aspect ratios above 30 in soda-lime glass and above 70 in fused silica. Aspect ratio here means hole depth divided by diameter.
Work published in the International Journal of Extreme Manufacturing reports crack-free, high-aspect-ratio holes in several glasses using femtosecond GHz-bursts. The short pulses limit the heat-affected zone, which is the main reason industry is moving this way. Research-grade results are not a promise for every production part. Hole quality still depends on glass composition, thickness and the exact laser regime.
Another laser route uses Bessel beams. A study on thin glass describes etching and drilling through-holes with picosecond Bessel beams, whose elongated focal zone suits thin material.
Choosing between them
| Factor | Mechanical diamond drilling | Ultra-short pulse laser |
|---|---|---|
| Typical use | Prototypes, low volume, simple round holes | Small diameters, tight tolerance, volume |
| Edge quality | Exit chipping and micro-cracks are the main risk | Crack-free, little or no taper in published work |
| Tool wear | Constant monitoring and tool changes | No tool contact |
| Throughput | Slow feed, hard to automate | Higher throughput for volume |
| Post-processing | Often cleaning and edge work | Less cleaning and deburring |
| Setup cost | Low | Higher, justified by volume or tolerance |
Mechanical drilling still has a niche. Sandvik Coromant points out that as medical and aerospace devices shrink, stack drilling, cross-hole drilling and machining on curved surfaces remain core skills for precision manufacturers. In glass, the practical question is whether the geometry and the edge requirement can be met without leaving damage that fails later.
Why the edge of the hole decides the life of the part
A chip at the exit of a hole is not cosmetic. It is a flaw from which a crack can start under thermal cycling, vibration or pressure. That matters most for:
- Medical devices, where a cracked window can compromise sealing or sterility.
- Aerospace and defence, where parts see vibration and temperature swings.
- Automotive dashboards, where cover glass has to survive years of heat and impact.
If the glass is to be strengthened, the order of operations matters. Holes are normally made before toughening or chemical strengthening, because drilling a strengthened piece releases the stored stress. Our guides to toughened glass and chemically strengthened glass explain how each process affects what can be machined afterwards. Coatings such as AR or AG and ceramic printing also go on after the holes are made, so the hole edge and the coating must be considered together.
How to specify a micro hole so it can be made and inspected
Most quoting delays come from drawings that say “hole, 1 mm” and nothing else. Give your supplier these items:
- Diameter and tolerance. State the allowed deviation, not just the nominal.
- Position tolerance. Say whether it is measured from an edge or a datum hole.
- Glass type and thickness. Soda-lime, borosilicate, aluminosilicate and fused silica all behave differently.
- Aspect ratio. Depth divided by diameter. A high ratio narrows the process options.
- Entry and exit edge limits. Give a maximum chip size or a chamfer requirement.
- Taper. Say whether a straight bore is needed or a slight cone is acceptable.
- Downstream processes. Strengthening, coating, printing or bonding.
- Quantity and delivery. One prototype and 10,000 parts rarely use the same process.
- Documentation. Batch traceability, inspection reports or compliance certificates.
Our guide to glass component design walks through these decisions in more detail. For the wider manufacturing picture, see our explanation of glass machining for engineers.
Design rules that save cost
- Keep holes away from edges and from each other. Close spacing raises the chance of breakout.
- Avoid holes very near corners.
- Do not specify a tolerance tighter than the function needs.
- Where possible, use one hole size across the part.
- Say early if the part will be toughened, so the holes are planned in.
Prototype first, then scale
A prototype run is the cheapest way to find out whether a hole design works. It shows chipping, fit and coating behaviour before tooling or programming is committed to volume. Mechanical routes often suit this first stage, while a laser route can make sense once the design is frozen and quantities rise. Our page on rapid glass prototyping explains how feature size affects turnaround.
Whatever the route, ask the supplier how the first-off parts will be inspected and how the result carries into production.
Health and safety when machining glass in the UK
If you machine glass in-house in the UK, the Control of Substances Hazardous to Health Regulations 2002 (COSHH) apply to dust and mist. The HSE’s guidance on controlling silica risk when working engineered stone is written for stone, not glass, but it sets out the controls that apply when cutting, grinding or polishing material that can release respirable crystalline silica (RCS). They include water suppression, local exhaust ventilation and respiratory protective equipment. It also warns that mist from water suppression needs controlling in its own right.
Water cooling does not remove the hazard. Before you start, have your health and safety lead or occupational hygienist assess the specific glass, the process and the extraction. HSE also publishes COSHH essentials guidance for stoneworkers that shows what good control practice looks like. If you buy drilled glass instead, this burden sits with your supplier, and you can ask how they manage it.
Our perspective
We see the same pattern on many enquiries. The hole is the last thing a designer draws and the first thing that fails in service. Our advice is to treat it as a process decision, not a dimension.
We work with engineering and procurement teams in medical, defence, aerospace, automotive, lighting and electronics. The question we ask first is what the part has to do after the hole is made: be strengthened, coated, printed, bonded or sealed. That answer decides the route. A hole that looks perfect under a loupe can still fail an audit if its edge condition was never defined or inspected.
For this reason we put traceability and inspection into the conversation at quotation stage. Our work runs under ISO 9001 certification with batch-level traceability, and we scale from prototype to volume. If your drawing has a micro-hole requirement, send it with the glass type, tolerance and quantity. We will tell you plainly what we can machine to specification and what needs a different approach.
— Alexandra
Working with Precision Glasses
We make custom glass components for demanding applications, with services including CNC glass machining, edge finishing, coated glass and custom components. We also supply optical components such as lenses, beam splitters and filters. Send us your drawing and specification for a review of your hole requirements. You can also read about our quality approach and the sectors we serve.
FAQ
What is the smallest hole you can drill in glass?
It depends on the method and the thickness. Mechanical drilling with solid diamond tools is the usual route under about 3 mm, and fine tools are fragile in thicker glass. Laser processes can go much smaller, and research reports high aspect ratios in thin glass. Quote the diameter and thickness together so a supplier can judge feasibility.
Can you drill glass after toughening?
No, not safely. Toughened and chemically strengthened glass hold stored stress, and drilling or cutting them can cause them to fail. Holes are made first, then the glass is strengthened. Plan the hole positions and edge finish before the strengthening step.
Why does glass chip when a hole is drilled?
Chipping happens mostly where the drill breaks through the exit face, because the unsupported glass fails. A sacrificial backing plate and coolant reduce it, but this slows the process. A non-contact laser avoids the mechanical force that causes it.
Is a laser always better than a drill for micro holes?
Not always. Lasers give better edge quality and suit volume, but mechanical drilling is cost-effective for prototypes and simple holes. The choice rests on your tolerance, edge requirement and quantity.
Does glass drilling dust fall under COSHH?
Yes, in a UK workplace, dust and mist from machining must be assessed under COSHH. HSE guidance on silica sets out controls such as water suppression, extraction and respiratory protection. Ask a qualified health and safety adviser to assess your specific glass and process.
Sources
- Micro-Hole Drilling on Glass Substrates: A Review
- Crack-free high-aspect ratio holes in glasses by top-down percussion drilling with infrared femtosecond laser GHz-bursts
- Etching and drilling of through-holes in thin glass by means of picosecond Bessel beams
- Sandvik Coromant: the new generation of micro drills
- Bullseye Glass: drilling small holes
- HSE: working engineered stone, control silica risk
- HSE: stoneworkers COSHH essentials
