H-K9L Optical Glass Cutting Test: TTV & Ra Results
Ensoll conducted this cutting test on H-K9L (Schott-type) optical glass supplied by a European customer. The objective was to produce 6 mm sheets from a 70 x 70 x 70 mm block while controlling thickness variation, Oberflächenrauheit, and edge chipping. The test used an ESO-GM endless diamond wire saw mit einem 0.45 mm fully coated Diamantdraht-Schlaufe.
- H-K9L crown optical glass — comparable to Schott N-BK7 in many applications — was cut from a 70 x 70 x 70 mm block into 6 mm sheets on an ESO-GM diamond wire saw with a 0.45 mm fully coated wire loop.
- Ten samples achieved TTV of 0.003-0.015 mm (8 von 10 at or below 0.010 mm), average thickness within +/-0.010 mm of nominal, mean Ra of 0.82 micrometers, and maximum edge chipping under 10 micrometers.
- Key process conditions: 24 m/s wire speed, a slow 5 mm/min feed, 160 N tension, cutting-oil lubrication, a 20-minute no-load wire pre-run, and wire-wear compensation adjusted from 0.47 An 0.48 mm.
- The data give engineers a practical baseline for precision slicing of optical glass before grinding and polishing; parameters should still be re-validated for each glass composition, geometry and quality requirement.
This test is one data point in a wider picture — the full method is described under optischer Glasschnitt.
Test Result at a Glance
- Finished sheet size: 6 x 70 x 70 mm
- TTV: 0.003-0.015 mm across 10 samples; 8 von 10 samples were at or below 0.010 mm
- Average thickness range: 5.992-6.008 mm
- Dicken-Toleranz: within +/-0.010 mm
- Average surface roughness (Ra): 0.72-0.94 micrometers; overall mean 0.82 micrometers
- Maximum edge chipping: below 10 micrometers for every sample
1. Test Object and Cutting Objective
H-K9L is a crown optical glass comparable to Schott N-BK7 in many optical applications. The supplied block measured 70 x 70 x 70 mm and had an approximate Mohs hardness of 6. The customer required 6 mm sheets with tight dimensional consistency and a cut surface suitable for subsequent grinding and polishing.
An endless diamond wire process was selected because its narrow kerf, continuous unidirectional cutting action, and controlled contact load are well suited to valuable hard and brittle materials. The process also helps limit vibration, material loss, and edge damage compared with conventional blade cutting.
2. Equipment, Draht, and Process Parameters
The test used the gantry-type ESO-GM diamond wire saw. Its rigid cast-iron structure, vertical top-down feed, automatic tension control, wire-break memory, and mist-removal system support stable precision cutting. A dedicated fixture was prepared for repeatable positioning of the 70 mm glass block.
| Parameter | Wert |
|---|---|
| Machine | ESO-GM |
| Wire specification | 0.45 x 1880 mm, fully coated |
| Wire feed speed | 5 mm/min |
| Schnittbreite | 70 mm |
| Drahtspannung | 160 N |
| Lineare Geschwindigkeit | 24 M/s |
| Wire bowing time | 60 s |
| Cooling and lubrication | Cutting oil |
Cutting oil was used for combined cooling and lubrication. Before cutting, the new Diamantdraht-Schlaufe was run without load for 20 minutes to remove loosely attached abrasive particles and stabilize the wire. During the test, the wire-diameter compensation value was adjusted from 0.47 An 0.48 mm in response to observed wire wear.
3. TTV Measurement Results
Total thickness variation (TTV) was measured on each 70 x 70 x 6 mm sheet using a nine-point grid and a dual-probe thickness measurement system on a vacuum adsorption stage. The instrument was thermally stabilized and calibrated with a standard thickness block before measurement. Each cleaned sample was centered on the stage, and vacuum adsorption was used to reduce the influence of substrate warpage.
| Probe | Neun-Punkte-Dickenwerte (mm) | Tmax | Tmin | TTV |
|---|---|---|---|---|
| S01 | 5.994, 5.991, 5.991 5.991, 5.992, 5.993 5.991, 5.992, 5.991 | 5.994 | 5.991 | 0.003 |
| S02 | 6.004, 6.001, 6.004 5.999, 6.002, 6.003 6.001, 6.002, 6.000 | 6.004 | 5.999 | 0.005 |
| S03 | 5.993, 5.998, 5.992 5.999, 5.996, 5.995 5.994, 5.997, 5.993 | 5.999 | 5.992 | 0.007 |
| S04 | 6.001, 6.000, 6.005 6.004, 6.002, 6.003 6.001, 6.004, 6.002 | 6.005 | 6.000 | 0.005 |
| S05 | 6.003, 6.000, 6.013 6.015, 6.008, 6.010 6.005, 6.007, 6.004 | 6.015 | 6.000 | 0.015 |
| S06 | 6.003, 6.002, 6.003 6.005, 6.004, 6.003 6.002, 6.004, 6.003 | 6.005 | 6.002 | 0.003 |
| S07 | 6.002, 6.000, 6.000 5.999, 6.001, 6.002 6.000, 6.001, 6.000 | 6.002 | 5.999 | 0.003 |
| S08 | 6.000, 5.998, 6.001 6.000, 5.999, 6.000 5.998, 6.001, 6.000 | 6.001 | 5.998 | 0.003 |
| S09 | 6.004, 5.995, 5.992 6.002, 6.000, 6.001 5.996, 5.998, 5.995 | 6.004 | 5.992 | 0.012 |
| S10 | 5.991, 5.990, 5.998 5.995, 5.994, 5.996 5.992, 5.995, 5.993 | 5.998 | 5.990 | 0.008 |
Result: TTV ranged from 0.003 An 0.015 mm. Eight of the ten samples were controlled within 0.010 mm, demonstrating repeatable thickness uniformity under the selected cutting conditions.
4. Thickness Dimensional Tolerance
The average of the nine measurements for each sample was compared with the nominal 6.000 mm thickness.
| Probe | Durchschnittliche Dicke (mm) | Abweichung (mm) |
|---|---|---|
| S01 | 5.992 | -0.008 |
| S02 | 6.002 | +0.002 |
| S03 | 5.996 | -0.004 |
| S04 | 6.002 | +0.002 |
| S05 | 6.008 | +0.008 |
| S06 | 6.003 | +0.003 |
| S07 | 6.000 | 0.000 |
| S08 | 6.000 | 0.000 |
| S09 | 6.000 | 0.000 |
| S10 | 5.994 | -0.006 |
Result: All sample averages were within +/-0.008 mm of the nominal thickness, meeting the +/-0.010 mm target.
5. Surface Roughness Results
Surface roughness was evaluated by stylus profilometry in accordance with ISO 4287. Three representative positions were measured on each sample: center, middle-left, and middle-right.
| Probe | Ra-1 | Ra-2 | Ra-3 | Average Ra (micrometers) |
|---|---|---|---|---|
| S01 | 0.86 | 0.91 | 0.90 | 0.89 |
| S02 | 0.82 | 0.85 | 0.86 | 0.84 |
| S03 | 0.91 | 0.95 | 0.93 | 0.93 |
| S04 | 0.87 | 0.92 | 0.91 | 0.90 |
| S05 | 0.92 | 0.96 | 0.94 | 0.94 |
| S06 | 0.73 | 0.76 | 0.75 | 0.75 |
| S07 | 0.74 | 0.76 | 0.75 | 0.75 |
| S08 | 0.80 | 0.83 | 0.82 | 0.82 |
| S09 | 0.70 | 0.73 | 0.72 | 0.72 |
| S10 | 0.79 | 0.82 | 0.81 | 0.81 |
Result: Average Ra values ranged from 0.72 An 0.94 micrometers, with an overall mean of 0.82 micrometers. The cut surfaces were suitable for subsequent precision grinding and polishing.
6. Edge-Chipping Results
All four edges of each sample were cleaned and inspected using an optically calibrated toolmaker’s microscope. The maximum defect observed along each edge was recorded.
| Probe | Position 1 | Position 2 | Position 3 | Position 4 | Maximum (micrometers) |
|---|---|---|---|---|---|
| S01 | 3.2 | 4.1 | 3.8 | 4.5 | 4.5 |
| S02 | 3.5 | 4.6 | 4.2 | 4.8 | 4.8 |
| S03 | 5.2 | 6.4 | 7.1 | 6.8 | 7.1 |
| S04 | 3.6 | 4.5 | 4.8 | 4.2 | 4.8 |
| S05 | 7.5 | 8.6 | 9.2 | 9.8 | 9.8 |
| S06 | 3.0 | 4.2 | 4.0 | 4.5 | 4.5 |
| S07 | 2.8 | 3.6 | 4.0 | 4.3 | 4.3 |
| S08 | 3.5 | 4.0 | 4.6 | 4.8 | 4.8 |
| S09 | 5.8 | 6.5 | 7.4 | 7.8 | 7.8 |
| S10 | 5.0 | 6.2 | 6.8 | 7.5 | 7.5 |
Result: Maximum chipping remained below 10 micrometers for every sample. The results indicate uniform edge loading and stable wire guidance during the cut.
7. Engineering Conclusion
This customer test demonstrates that the endless diamond wire process can produce thin H-K9L optical glass sheets with controlled thickness, low surface roughness, and limited edge chipping. Process stability depended on the coordinated use of a rigid gantry machine, controlled wire tension, a slow 5 mm/min feed, cutting-oil lubrication, wire pre-running, and wear compensation.
The data provide a practical baseline for engineers evaluating precision separation of optical glass before grinding and polishing. Actual production parameters should still be validated for each glass composition, block geometry, fixture, and downstream quality requirement.
Discuss Your Optical Glass Cutting Requirement
Ensoll provides sample testing, machine selection, diamond wire specification, fixtures, and process development for optical glass and other hard and brittle materials. Review the ESO-GM machine, explore our optische Glasschneidemaschine, oder send your material dimensions and target tolerances for an application review.
Häufig gestellte Fragen
What TTV can diamond wire cutting achieve on optical glass?
In this H-K9L test on 6 mm sheets, total thickness variation ranged from 0.003 An 0.015 mm across ten samples, with eight samples at or below 0.010 mm. Results depend on machine rigidity, wire condition, tension control and feed strategy.
Is H-K9L the same as Schott N-BK7?
They are comparable crown optical glasses used in many of the same optical applications. H-K9L has a Mohs hardness of about 6 Aluminiumschmelzofen mit Regenerativbrenner, like N-BK7, is widely used for lenses, prisms and windows — but they are not identical formulations, so processing parameters should be validated per material.
What surface roughness does diamond wire cutting leave on optical glass?
In this test, average Ra values ranged from 0.72 An 0.94 micrometers with an overall mean of 0.82 micrometers, measured by stylus profilometry per ISO 4287. Surfaces at this level are suitable for subsequent precision grinding and polishing.
Why should a new diamond wire loop be pre-run before cutting?
A short no-load pre-run — 20 minutes in this test — removes loosely attached abrasive particles and stabilizes the wire before it touches the workpiece. Combined with wear compensation during the cut, this keeps thickness and surface quality consistent across samples.
Reviewed by the Ensoll engineering team.
