Quick answer: Polishing Borofloat 33 covers Borofloat 33 (CTE 3.25 x 10^-6 /K, 350 nm – 2.0 um); Polishing to flatness to lambda/4 per 25 mm. Prototypes ship in 5-10 working days.
polishing borofloat 33 is a materials problem before it is a machining problem. Borofloat 33 has float-glass flatness off the line and a Knoop hardness of 480 kg/mm2, so the polishing recipe – feeds, coolant, tooling – differs from what works on ordinary float glass. The line runs pitch and polyurethane pad polishers with cerium oxide slurry and holds flatness to lambda/4 per 25 mm.
Key parameters
| Material | Borofloat 33 (SCHOTT float production, wafer grade) |
|---|---|
| Thermal expansion (CTE) | 3.25 x 10^-6 /K |
| Service temperature | 450 C continuous |
| Transmission range | 350 nm – 2.0 um |
| Density | 2.23 g/cm3 |
| Knoop hardness | 480 kg/mm2 |
| Refractive index | 1.471 @ 587 nm |
| Stock thickness | 0.70 – 25.4 mm |
| Maximum blank size | 500 x 500 mm |
| Process | Polishing |
| Working tolerance | flatness to lambda/4 per 25 mm |
| Minimum feature | Ra below 1 nm |
| Surface finish | scratch-dig 40/20 to 20/10 |
| Thickness window | 0.2 – 50 mm |
| Edge condition | polished bevels available |
| RFQ inputs | PDF/DXF/STEP drawing, quantity brackets, surface and edge spec |
Design guidance
Three items decide most of the cost and lead time on this work:
- Material note: float tin side must be tracked when parts see coating or bonding steps.
- Process boundary: steep aspect parts and deep pockets polish unevenly; those faces are specified as fine-ground.
- Over-specification is the quiet budget killer: a 20/10 scratch-dig face costs roughly three times an 80/50 face, so grade each surface individually.
The full rules live in our tolerance design guide and holes and edges design guide.
Process window
Polishing earns its place through optical-grade faces with certified scratch-dig and interferometer-verified flatness. Its boundary condition – steep aspect parts and deep pockets polish unevenly; those faces are specified as fine-ground – is the first thing our DFM review checks.
Beyond this page, Borofloat 33 routinely runs through etching, ultrasonic machining, lapping, cnc machining in our shop – most real parts combine two or three of these steps.
Typical applications
Orders for polishing borofloat 33 cluster in led packaging (groove covers, phosphor carriers, package windows); mems devices (cap wafers, TGV substrates, motion-sensor lids); optical sensors (sensor windows, filter caps, lens covers). Background reading on the underlying material science: SCHOTT BOROFLOAT product page.
Dimensions still moving? Configure this part live in the 3D builder below, or open the full custom glass machining 3D builder to start from a blank canvas.
For adjacent specifications, see optical polishing capability, wafer dicing process, glass sandblasting.
Buyer questions, answered
What tolerances are achievable on Borofloat 33 parts?
Ground features hold +/-0.01 mm and lapped thickness reaches +/-0.003 mm. Float tin side must be tracked when parts see coating or bonding steps.
What thickness range do you stock for Borofloat 33?
Standard stock spans 0.70 – 25.4 mm, with blanks up to 500 x 500 mm. Other formats are sourced per order.
How does Borofloat 33 behave under heat?
CTE is 3.25 x 10^-6 /K and continuous service reaches 450 C continuous, which is what drives its use where float-glass flatness off the line matters.
What accuracy does polishing hold?
Flatness to lambda/4 per 25 mm with minimum features of Ra below 1 nm. Steep aspect parts and deep pockets polish unevenly; those faces are specified as fine-ground.
What equipment runs the polishing work?
Pitch and polyurethane pad polishers with cerium oxide slurry.
Specifications on this page were last reviewed by our engineering team in July 2026.