Okuma GI-20NII

$220,000 - $310,000 Updated 2026-03-13

Key Specifications

X Travel

165 mm (6.50 in)

Z Travel

150 mm (5.91 in)

Rapid Traverse

max bore diameter

200 mm (7.9 in)

min bore diameter

20 mm (0.8 in)

max bore depth

150 mm (5.9 in)

Overview

The Okuma GI-20NII is the larger model in Okuma's GI internal grinding series, handling bore diameters from approximately 20 mm to 200 mm (0.8 to 7.9 in) with bore depths up to 150 mm (5.9 in). This expanded capacity compared to the GI-10NII opens up larger bearing housings, gear bores, turbine components, and heavy-duty hydraulic cylinder bores that require precision internal grinding.

The internal grinding spindle system accommodates speeds from approximately 5,000 to 40,000 RPM depending on the spindle unit installed. The lower maximum speed compared to the GI-10NII reflects the larger wheel diameters used for bigger bores, where adequate peripheral speed is achieved at lower RPM. Multiple interchangeable spindle units cover the full bore diameter range. The spindles use precision bearings with oil-air lubrication.

The X-axis (infeed) travel is 165 mm (6.50 in) with a minimum feed increment of 0.0001 mm (0.000004 in). The Z-axis travel is 150 mm (5.91 in). The workhead spindle provides rotation from 40 to 500 RPM. Workholding options include precision chucks and faceplates for larger workpieces. Face grinding capability allows simultaneous bore and face grinding in a single setup.

The GI-20NII includes Okuma's gap elimination for reduced air grinding time, in-process bore gauging for automatic size control, and programmable multi-step grinding cycles. The OSP-P300G control stores multiple part programs and manages the grinding cycle from rough through finish and spark-out. The machine accommodates multiple grinding operations in sequence for complex bore profiles including taper bores, step bores, and face/bore combinations.

Machine weight is approximately 5,000 kg (11,023 lb). Floor space runs approximately 3,200 x 2,400 mm (126 x 94 in). New pricing typically ranges from $220,000-$310,000. The GI-20NII competes with Studer S141/S151, Danobat IRD, and Kellenberger ID grinders for medium to large bore precision grinding applications.

Full Specifications

Parameter	Value
Max Bore Diameter	200 mm (7.9 in)
Min Bore Diameter	20 mm (0.8 in)
Max Bore Depth	150 mm (5.9 in)
Max Workpiece Od	300 mm (11.8 in)
Grinding Spindle Speed	Up to 40,000 RPM
X-Axis Travel	165 mm (6.50 in)
Z-Axis Travel	150 mm (5.91 in)
Min Feed Increment	0.0001 mm (0.000004 in)
Workhead Speed	40 - 500 RPM
Face Grinding	Yes
Machine Weight	5,000 kg (11,023 lb)
Floor Space	3,200 x 2,400 mm (126 x 94 in)
CNC Control	Okuma OSP-P300G
Workholding	Chuck, faceplate, or collet
Bore Range With 100mm Od Wheel	Ø5-300
Max Grinding Length 1ws 2ws	200
Max Grinding Length Center Rest Option	300
Max Grinding Length 4ws	130
Workhead Spindle Bore	Ø70
Rapid Traverse Rate	12
Available Spindles	max: 40,000 rpmmax: 150,000 rpm
Okuma Global Repair Center	Charlotte, North Carolina
Inches	Metric

Specifications sourced from okuma.com — verified 2026-03-28

Strengths & Limitations

Strengths

200 mm maximum bore diameter handles medium to large ID grinding applications including bearing housings, gear hubs, and turbine components
150 mm bore depth capacity exceeds the GI-10NII's 100 mm, enabling deeper bore grinding on larger components
Combined bore and face grinding in a single setup eliminates secondary operations and improves bore-to-face perpendicularity
In-process bore gauging provides automatic size control with wheel retraction at target diameter, ensuring consistent bore dimensions in production
Multiple interchangeable spindle units cover a wide bore diameter range from 20 mm to 200 mm without machine changeover
5,000 kg machine mass provides stable vibration damping for precision grinding on larger workpieces

Limitations

200 mm maximum bore may be limiting for very large bore applications; specialized chucking grinders or boring operations may be needed for larger IDs
Interchangeable spindle units for different bore ranges add to the total investment and require careful handling and storage
OSP-P300G control requires training for operators not familiar with Okuma's grinding control interface
Internal grinding wheels are consumables that wear faster than OD grinding wheels, increasing ongoing cost per part
3,200 x 2,400 mm footprint is larger than the GI-10NII, requiring more floor space for the extended bore capacity

Best For

Bearing manufacturers grinding larger bearing race IDs, housing bores, and roller components in the 50-200 mm bore range Automotive manufacturers grinding transmission housing bores, differential case IDs, and large gear hub bores Aerospace manufacturers grinding turbine bearing housings, actuator cylinder bores, and landing gear component IDs Hydraulic equipment manufacturers grinding large cylinder bores, valve housing IDs, and pump body bores to tight tolerance Power generation shops grinding generator bearing housings, turbine seal bores, and large coupling component IDs

Frequently Asked Questions

01 What does an Okuma GI-20NII cost?

New pricing ranges from $220,000-$310,000 depending on the number of spindle units, in-process gauging configuration, and automation options. Additional spindle packages for different bore ranges add to the base investment. The price is competitive with European ID grinders from Studer and Kellenberger.

02 How does the GI-20NII compare to the GI-10NII?

The GI-20NII handles bores up to 200 mm vs the GI-10NII's 100 mm, with 150 mm depth vs 100 mm. The GI-20NII uses lower-speed spindles (40,000 RPM max vs 60,000) because larger wheels achieve adequate speed at lower RPM. The GI-10NII is better optimized for very small precision bores. For shops grinding a range of bore sizes, the GI-20NII offers more flexibility.

03 Can the GI-20NII grind taper bores?

Yes. The OSP-P300G control programs taper grinding cycles using simultaneous X and Z axis interpolation. The machine grinds straight bores, taper bores, step bores, and combined bore/face profiles. Taper grinding accuracy depends on the taper angle and length, with steeper tapers requiring careful parameter optimization.

04 What roundness can the GI-20NII achieve?

With proper setup and process development, bore roundness of 0.5-1.0 micrometers is achievable depending on bore size, material, and grinding parameters. Larger bores tend to achieve slightly looser roundness than small bores due to wheel deflection effects. In-process gauging helps maintain consistency across production runs.