Surface grinding machine G-250 ZnSe ZnS

flatopticaldigital

Overview
A large-aperture ZnSe / ZnS optics grinding machine (G-250) purpose-built for chalcogenide IR work: CO₂ laser windows, multispectral meniscus lenses and large-aperture thermal-imaging primaries. Wheel grit, coolant pH and infeed cadence are tuned to the {110} cleavage plane to minimize edge chipping on ZnSe and ZnS.

Key metrics

• Workpiece range: Ø 80–250 mm
• Surface form: ±0.005 mm
• Edge chipping target: < 0.2 mm
• Centering: ≤ 20″ (arc-seconds)

The Machine
Cast-iron base, NSK-bearing spindle, integrated centroscope; same precision family as the G-100 but scaled for Ø 80–250 mm workpieces. Ships with a dedicated coolant tank sized for a water-soluble emulsion calibrated to chalcogenide-safe pH.

Build / configuration (standard)

• Workpiece range: Ø 80–250 mm · thickness ≤ 45 mm
• Positioning accuracy: ±0.003 mm
• Spindle runout: radial & axial within 0.005 mm
• Spindle vibration: ≤ ±3 µm displacement
• Bearings: NSK 7203C / 7005AC P4, mechanical, natural air-cooled
• Control: PLC + servo · English HMI · handheld controller
• Coolant: water-soluble emulsion · pH near 7 (chalcogenide-safe)

What the G-250 does differently

• Large-aperture range Ø 80–250 mm built for CO₂ laser windows, multispectral primaries and defense-grade thermal-imaging objectives.
• Wheel grit calibrated for chalcogenides: 350–400 grit electroplated nickel-bond on a #45 steel base, with a lighter dressing routine than for harder materials.
• Coolant pH near neutral (6.8–7.4) and pH verification included to prevent surface clouding on ZnSe.
• Spindle vibration kept ≤ ±3 µm to bound edge chipping on Mohs 4–4.5 materials.
• Centering to ≤ 20″ across large apertures using an extended centroscope arm.
• Programmable wheel-approach offset per material to avoid tearing the {110} cleavage plane.

How it grinds — wheel, coolant and dressing
Standard wheel: 350–400 grit electroplated nickel-bond cup on a #45 steel base. ZnSe loads the wheel faster; recommended re-dress cadence for ZnSe Ø 100 mm is every 30–40 parts. The machine ships with a water-soluble emulsion calibrated to pH 6.8–7.4 at 5–8% concentration and includes a pH meter at the coolant tank. Wheel-approach offset profiles are programmable and shipped pre-set for ZnSe / ZnS.

Material guidance

• ZnSe — Mohs 4–4.5, cleaves on {110}. Requires near-neutral coolant pH 6.8–7.4 (5–8% emulsion). Used for CO₂ laser windows and MWIR/LWIR optics.
• ZnS (standard / FLIR grade) — Mohs ~3, polycrystalline CVD; more forgiving on pH but sensitive to coolant concentration.
• ZnS (multispectral HIP/CVD) — Mohs ~4, dress the wheel between part groups due to batch grain-structure variability.
• Also capable of Ge, Si, sapphire and optical glass with adjusted wheel choice and infeed.

Comparison — bonded-grit grinding vs other approaches
Approach | Form tolerance | Edge chip | Cycle / face | Operator skill
Hand lapping (cast iron + slurry) | varies by operator | < 0.1 mm if good | hours | high
Full CNC freeform grinder | ±0.005 mm | < 0.2 mm | 2–3 min | CNC programmer
G-250 bonded-grit (this spec) | ±0.005 mm | < 0.2 mm | 1–2 min | PLC + handheld

Datasheet (summary table)
Workpiece diameter | Ø 80 – 250 mm
Workpiece thickness | ≤ 45 mm
Surface types | convex · concave · flat (same spindle)
Axis positioning accuracy | ±0.003 mm
Spindle radial / axial runout | within 0.005 mm
Spindle vibration (displacement) | ≤ ±3 µm
Surface form after grinding | within 0.005 mm
Centering tolerance (centroscope) | ≤ 20" arc-seconds
Diameter tolerance | ±0.01 mm
Roundness | ≤ 0.01 mm
Edge chipping (ZnSe / ZnS) | < 0.2 mm
Shipped wheel | 350–400 grit electroplated nickel-bond on #45 steel base
Re-dress cadence (ZnSe Ø 100 mm) | every 30–40 parts
Coolant | water-soluble emulsion · pH 6.8–7.4 · 5–8% concentration
pH verification | pH meter included at coolant tank
Bearings | NSK 7203C / 7005AC P4 — mechanical, natural air-cooled
Linear guides | 4-direction equal-load preload precision rail
Ball screws | single-nut un-flanged rolled C7 preload
Control | PLC + servo · English HMI · handheld controller
Wheel-approach offset | programmable per material profile via HMI
Drawing standard | ISO 10110
Service life (well-maintained, dedicated coolant loop) | 20–30 years

Free trial / production note
Free trial grind available: send a ZnSe or ZnS blank and a finished-lens drawing; supplier can run a proof part and return it with a metrology report. The G-250 is a spherical generator (not a freeform CNC grinder); for large departures from best-fit sphere a full CNC freeform grinder is recommended.

Caractéristiques / spécifications techniques

• Model: G-250
• Workpiece diameter: Ø 80–250 mm
• Workpiece thickness: ≤ 45 mm
• Axis positioning accuracy: ±0.003 mm
• Surface form after grinding: ±0.005 mm
• Spindle radial/axial runout: ≤ 0.005 mm
• Spindle vibration: ≤ ±3 µm displacement
• Centering tolerance: ≤ 20" arc-seconds
• Diameter tolerance: ±0.01 mm · Roundness ≤ 0.01 mm
• Edge chipping (ZnSe / ZnS): < 0.2 mm
• Shipped wheel: 350–400 grit electroplated nickel-bond on #45 steel base
• Re-dress cadence (ZnSe Ø 100 mm): every 30–40 parts
• Coolant: water-soluble emulsion, pH 6.8–7.4, 5–8% concentration · pH meter supplied
• Bearings: NSK 7203C / 7005AC P4
• Control: PLC + servo, English HMI, handheld controller
• Wheel-approach offset: programmable per material profile via HMI