Custom Sapphire Geometries: Drilling, Threading, Polishing & Complex Shapes
Sapphire is one of the strongest and hardest engineering materials available for optics, sensors, furnaces, plasma systems, and precision instruments.
However, its hardness (9 Mohs) and brittleness mean that sapphire cannot be machined like metal — it requires diamond grinding, ultrasonic machining, or laser shaping.
This guide explains which geometries are achievable, their limitations, and what customers should know before designing custom components.
What Shapes Can Be Manufactured from Sapphire?
You can fabricate sapphire into many useful geometries:
- ✔ Rods
- ✔ Tubes (ID/OD custom sizes)
- ✔ Windows & plates
- ✔ Lenses & prisms (optical grade)
- ✔ Rings & spacers
- ✔ Nozzles
- ✔ Custom chambers
- ✔ Sapphire washers
- ✔ Sapphire wafers
Sapphire is extremely flexible in shape as long as machining rules are respected.
Drilling Capabilities (Holes in Sapphire)
Due to sapphire’s hardness, drilling is done by ultrasonic machining or diamond core drilling.
Typical capabilities:
| Parameter | Value |
|---|---|
| Minimum hole diameter | 0.2–0.3 mm |
| Deep hole aspect ratio | 6:1 to 8:1 |
| Positional tolerance | ±0.05–0.1 mm |
| Edge chipping | 20–50 µm (improved with polishing) |
Notes:
- Holes smaller than 0.2 mm require laser drilling only
- Deep holes (>10 mm depth) increase cost dramatically
- Thin-walled tubes must be handled carefully to avoid cracking
Threading Capabilities (Internal & External Threads)
Sapphire threads can be made, but with important limitations.
Best practice:
- Large threads only (≥ M4 recommended)
- Not suitable for fine pitches
- Thread depth limited due to brittleness
Why sapphire threads are difficult:
- Threads create stress concentration → risk of fracture
- Diamond tools cannot make sharp edges → threads must be rounded
- Ultrasonic machining produces limited detail
Recommended alternatives:
- Use sapphire + metal insert
- Use clamping, slip fits, or O-ring sealing
- Use bonding rather than threading
Slotting, Grooving, and Custom Channels
Achievable:
- Straight slots ≥ 0.2–0.3 mm
- Circular grooves
- Keyways
- Alignment channels
Limitations:
- Minimum radius at corners: 0.1–0.3 mm
- Channels deeper than 3–4 mm become difficult
- Tight tolerance slots require slower machining
Polishing Options for Custom Sapphire Parts
| Surface | Typical Finish | Use Case |
|---|---|---|
| Optical face | Ra 10–20 Å | Windows, lenses |
| Fine-polished side wall | Ra < 0.1 µm | Optical tubes |
| Lapped surface | Flat, matte | Furnace components |
| Ground-as | Ra 0.3–1.0 µm | Mechanical parts |
Optical polishing significantly increases cost due to long processing time.
Complex Shapes & 3D Machining
Modern ultrasonic machining allows:
✔ 3D contours
✔ chambers
✔ cones
✔ sapphire nozzles
✔ recessed surfaces
✔ multiple-step geometries
However:
- Sharp internal corners impossible
- Very thin sections (<0.3 mm) tend to crack
- Deep complex features raise lead time & cost
Design Limitations (Critical for Customers)
| Feature | Limitation |
|---|---|
| Minimum wall thickness | ≥0.3–0.5 mm |
| Minimum corner radius | 0.1–0.3 mm |
| Minimum slot width | ≥0.2–0.3 mm |
| Threading | Only large threads (M4+) |
| Hole diameter | ≥0.2–0.3 mm |
| Deep holes | AR ≤ 6:1–8:1 |
| Long thin rods | Must consider bending stress |
What Customers Must Provide for Custom Sapphire Jobs
Required:
- Dimensions & tolerances
- Surface finish requirements
- Whether optical-grade polishing is needed
- Application conditions: temperature, pressure, optical wavelength
Optional:
- Crystal orientation (C-plane, A-plane, R-plane)
- Coating requirements
- Furnace or plasma chamber specifications
Frequently Asked Questions
Q1. Can sapphire be drilled?
Yes — minimum hole size is typically 0.2–0.3 mm.
Q2. Can sapphire be threaded?
Yes, but only large threads (M4 or larger).
Q3. Can sapphire be polished optically?
Yes — Ra 10–20 Å is achievable.
Q4. Can sapphire have sharp internal corners?
No — minimum radius is 0.1–0.3 mm.
Q5. What shapes are possible?
Rods, tubes, windows, chambers, cones, slots, nozzles, and many custom geometries.
