Large Lens Curve Generator SG-120
A manual large lens curve generator that grinds a convex, concave or flat surface on optics up to Ø120 mm. It is the SG-80’s bigger brother — more spindle power, internal-jet dual cooling and a stiffer structure to hold a radius on a large face.
What this machine makes, and what happens before and after it
An optical element starts as a sawn or pressed blank and ends as a coated, centred lens. A large lens curve generator owns the step in the middle for the biggest parts: it cuts the radius of curvature into the face of a blank up to Ø120 mm and brings the centre thickness close to the drawing. Everything upstream supplies it; everything downstream inherits the surface it leaves.
The part that leaves this machine is not finished; its radius is close enough that the lapping and polishing stage removes microns rather than re-cutting the curve. What is different at Ø120 is not the principle — it is the load. A big blank takes more cutting force and throws off more heat, and that is what the SG-120 is built for.
For parts up to Ø80 mm the smaller SG-80 spherical lens curve generator covers the same principle at lower cost. Step up to the SG-120 when the diameter, the cutting force or the heat of a large face is what your parts demand.
How does a large lens curve generator produce a radius?
The same way the smaller machines do — no template, no copy former. On this class of machine the radius comes out of an angle.
Two spindles do the work. The tool spindle carries a diamond cup wheel and turns it at 8,000 rpm. The workpiece spindle holds the blank on a vacuum chuck, rotates it at 0–36 rpm and feeds it into the wheel while the operator watches the cut.
Because the cup wheel is tilted, its circular cutting edge sweeps out a sphere as the blank turns underneath it. The radius of that sphere is fixed by geometry alone:
- sin θ = d / (2R) — where θ is the spindle tilt, d the effective cutting-edge diameter of the cup wheel, and R the radius produced
- θ = 0° — the two axes are parallel and the machine generates a plane
- tilt 0–45° — the steeper the setting on the rotating carriage, the shorter the radius produced
- Convex or concave — decided by which side of the workpiece axis the wheel is tilted to
The geometry is identical to the smaller machines. What a large lens curve generator has to add is the strength and cooling to hold that geometry while it removes far more glass.
You are buying a range set by the 0–45° carriage and the wheels for your material — the same as on the smaller machines. The difference you pay for on the SG-120 is capacity, not a different principle.
Why does a large lens need a different machine?
Not because the geometry changes — it does not. Because a big blank takes more force to cut and sheds more heat, and a machine sized for Ø80 cannot hold form under that load. Three things are built up on the SG-120.
More spindle power for the bigger cut
The tool and workpiece motors are raised to 1.5 kW × 2 poles, so the machine keeps its cutting speed through the wider arc of a Ø120 face instead of bogging down and chattering.
Internal-jet dual-path cooling
The tool spindle carries an internal jet, so coolant reaches the cut from inside the wheel as well as outside. On a large face that inner-plus-outer supply is what keeps the surface quality up as heat rises.
Reinforced, stiffer structure
Load-bearing parts are strengthened over the SG-80 to add rigidity, so the extra cutting force of a large blank does not show up as form error on the finished face.
Still a manual machine to master
Like the SG-80, the operator sets the tilt, runs a first part and reads its sagitta before the run. The SG-120 gives that skilled operator the capacity to work large glass, not a different way of working.
Which materials and geometries can it handle?
| Item | Capability |
|---|---|
| Surfaces generated | Convex and concave spherical surfaces; plane (flat) surfaces |
| Radius range | Set by the rotating carriage, tilt 0°–45°; flat at 0° |
| Workpiece diameter | Up to Ø120 mm |
| Workpiece stroke | 70 mm |
| Workpieces per cycle | 1 — single-part, manual load |
| Materials | Optical lenses — send your material for a free trial run; suitability confirmed on your own parts |
| Surface-form accuracy | ≤ 0.003 mm |
| Centre-thickness error | ≤ 0.01 mm |
| Cooling | Internal-jet dual path (inner + outer) |
If your drawings are dimensioned to the ISO 10110 framework, send one with the enquiry. On a large lens curve generator the radius tolerance and centre-thickness tolerance are what decide whether the job fits, and whether the diameter needs the bigger machine — see the optical materials data if you are choosing glass.
Technical specifications
The SG-120 shares the SG-80’s accuracy grades; it adds spindle power, internal-jet cooling and a reinforced structure for large work.
| Max machining diameter | Ø120 mm |
| Workpiece stroke | 70 mm |
| Rotating carriage tilt | 0° – 45° |
| Tool spindle speed | 8,000 rpm |
| Workpiece spindle speed | 0 – 36 rpm, stepless |
| Tool spindle runout (radial / axial) | ≤ 0.005 mm |
| Workpiece spindle runout (radial / axial) | ≤ 0.005 mm |
| Two-axis height match | ± 0.25 mm, adjustable |
| Surface-form accuracy | ≤ 0.003 mm |
| Centre-thickness error | ≤ 0.01 mm |
| Cooling | Internal-jet, dual path (inner + outer) |
| Spindle motor | 1.5 kW × 2 poles |
| Workpiece motor | 0.18 kW (1:30) |
| Overall dimensions (L × W × H) | 1.3 × 1.0 × 1.5 m |
| Total weight | approx. 600 kg |
| Base construction | Cast iron, hand-scraped mating surfaces, reinforced |
On a large lens curve generator the diamond cup wheels and dressing stones are process consumables chosen for the material and the radius. They are quoted separately — tell us your materials and radii and we will specify them.
Main assemblies and what each one is for
This is the vocabulary your operator and our service engineer will share on the shop floor.
| Assembly | Function |
|---|---|
| Tool spindle | Carries the diamond cup wheel at 8,000 rpm; 1.5 kW × 2-pole motor for the large-work cut |
| Internal-jet cooling | Feeds coolant from inside the wheel as well as outside, holding surface quality on a large face |
| Rotating carriage | Tilts the tool spindle 0°–45° to set the generated radius; locked for the run |
| Workpiece spindle | Vacuum chuck rotating the blank at 0–36 rpm; hand feed against the wheel |
| Coolant system | Circulating supply feeding the internal and external paths, tank in the base |
| Reinforced cast-iron base | Strengthened hand-scraped structure holding form under the higher cutting force |
| Operator controls | Spindle speed, feed and carriage lock within reach of the working position |
Utilities, environment and safety
Electrical supply, compressed air, coolant, floor loading and the ambient conditions the machine is to run in are confirmed with us for each order, together with the safety and protective arrangement supplied with it. These figures depend on the voltage and frequency of your site, the material you are running and the destination market, so we do not publish a single set of them here.
Send us the site conditions with your enquiry and we will return the utility and environmental requirements in writing, before the order is placed.
A large lens curve generator is only as repeatable as the operator running it, and large glass is less forgiving of a heavy feed than small glass. Settling the feed and cooling for a new large part takes trial parts, not a manual — the reason we ask for your blanks before quoting.
What happens after the machine is installed?
The same terms apply to every machine we ship, wherever in the world it goes.
| Warranty period | 12 months from final acceptance |
| Response during warranty | Response within 8 hours · solution proposed within 24 hours · issue resolved within 48 hours, including procurement, installation and commissioning of parts |
| After the warranty period | Service and spare parts available for the life of the machine |
| Certification | CE |
Specifications are subject to change as a result of design upgrades. Minor differences may occur at certain parts. For a binding specification, refer to the order confirmation.
See the machine running
The SG-120 generating a large spherical surface, and the internal-jet cooling holding the cut on a Ø120 face.
01 — Spherical generating cycle, large blank
02 — Internal-jet cooling and carriage setup
Send one drawing and a few blanks
A large lens curve generator is easy to specify badly from a datasheet. Send us one element drawing — diameter, radius, centre thickness, material and the tolerance grade you have to hold — together with a few of your own blanks. We run them, return them, and send the process sheet with the quotation.
If your parts are Ø80 mm or smaller, we will point you to the SG-80 instead of quoting a machine bigger than you need.
12-month warranty · free trial run on customer-supplied material
Optics customers include Edmund Optics and Coherent
Related equipment and reading:
- Spherical lens curve generator SG-80 — the smaller manual generator up to Ø80 mm
- CNC optical curve generator Auto-SG-50 — the automated generator
- Convex lens polishing machine FP-4L — the polishing stage downstream
- Optical lens fabrication line — how the stations connect