Okuma GI-20NII

Est. $220,000 - $310,000 Specs verified 2026-10-03 · okuma.com Updated 2026-10-03

Image: d30jruhmdicmo0.cloudfront.net, Okuma

Key Specifications

Rapid Traverse

12 m/min (472 ipm)

max bore diameter

200 mm (7.9 in)

min bore diameter

20 mm (0.8 in)

max workpiece od

300 mm (11.8 in)

grinding spindle speed

Up to 40,000 RPM

control

Okuma OSP-P300G

How much does the Okuma GI-20NII cost?

Estimated price range

Est.$220,000 - $310,000

Our best estimate for a cnc grinding machine in this class — not a quote from Okuma. Configuration moves it a long way.

Overview

The Okuma GI-20NII is a CNC internal grinder controlled by the Okuma OSP-P300G. What distinguishes its specification is that the grinding length depends on how the machine is configured: 200 mm (7.87 in) in the 1WS and 2WS versions, 130 mm (5.12 in) in the 4WS version, and 300 mm (11.81 in) when the center rest option is fitted.

That spread is the first thing to settle. A buyer who needs the 300 mm figure is buying the center rest, which is an option, and one who chooses the 4WS configuration accepts the shortest grinding length of the three.

Two wheel-spindle types are listed. Belt-driven spindles run to a maximum of 40,000 rpm and high-frequency spindles to a maximum of 150,000 rpm. Wheel speed in internal grinding is governed by the small wheel that has to fit inside the bore, so the high-frequency spindles are what make small bores practical, while the belt-driven type covers larger wheels and bores.

The workhead spindle bore is Ø70 mm (Ø2.76 in), which sets what can pass back into the spindle. Rapid traverse is 12 m/min (472 ipm). The smaller GI-10NII is listed at 20 m/min (787 ipm) on X and 30 m/min (1,181 ipm) on Z, so the GI-20NII is the slower of the two between passes. Okuma ties its bore-diameter range to a stated wheel diameter, so the usable range should be confirmed for the wheel and spindle actually specified.

Full Specifications

Parameter	Value
Max Bore Diameter	200 mm (7.9 in)
Min Bore Diameter	20 mm (0.8 in)
Max Workpiece OD	300 mm (11.8 in)
Grinding Spindle Speed	Up to 40,000 RPM
CNC Control	Okuma OSP-P300G
Bore Range with 100mm OD Wheel	Ø5-300
Max Grinding Length 1ws 2ws	200 mm (7.87 in)
Max Grinding Length Center Rest Option	300 mm (11.81 in)
Max Grinding Length 4ws	130 mm (5.12 in)
Workhead Spindle Bore	Ø70 mm (Ø2.76 in)
Rapid Traverse Rate	12 m/min (472 ipm)
Available Spindles	max: 40,000 rpm max: 150,000 rpm Belt Driven High Frequency
Bore Range with 100mm 3 95 OD Wheel	Ø5-300 mm (Ø0.20-11.81 in)

Specifications sourced from okuma.com — verified 2026-10-03

Strengths & Limitations

Strengths

Grinding length of 200 mm (7.87 in) in the 1WS and 2WS versions, extendable to 300 mm (11.81 in) with the center rest option
High-frequency wheel spindles to a maximum of 150,000 rpm for small bores
Belt-driven wheel spindles to a maximum of 40,000 rpm
Okuma OSP-P300G control and a Ø70 mm (Ø2.76 in) workhead spindle bore

Limitations

The 4WS version is limited to a 130 mm (5.12 in) grinding length
The 300 mm (11.81 in) grinding length requires the center rest option
Rapid traverse is 12 m/min (472 ipm), below the 20 m/min (787 ipm) and 30 m/min (1,181 ipm) of the GI-10NII

Best For

Internal grinding to a 200 mm (7.87 in) length in 1WS or 2WS form Long bores to 300 mm (11.81 in) with the center rest option Small-bore work using high-frequency spindles up to 150,000 rpm Production cells built around the Okuma OSP-P300G control

Frequently Asked Questions

01 What is the maximum grinding length of the GI-20NII?

It depends on the configuration. Okuma lists 200 mm (7.87 in) for the 1WS and 2WS versions and 130 mm (5.12 in) for the 4WS version. With the center rest option the maximum grinding length is 300 mm (11.81 in).

02 What wheel spindles are available on the GI-20NII?

Okuma lists two types: belt-driven spindles with a maximum of 40,000 rpm and high-frequency spindles with a maximum of 150,000 rpm. Choose by bore size, since a small wheel needs high rotational speed to reach a workable surface speed.

03 Which control does the GI-20NII use?

The Okuma OSP-P300G, Okuma's own control. Rapid traverse on the machine is listed at 12 m/min (472 ipm) and the workhead spindle bore is Ø70 mm (Ø2.76 in).

04 How does the GI-20NII differ from the GI-10NII?

By the listed rapid rates, the GI-10NII is the faster machine at 20 m/min (787 ipm) on X and 30 m/min (1,181 ipm) on Z, against 12 m/min (472 ipm) on the GI-20NII. The GI-20NII page lists the OSP-P300G control and grinding lengths from 130 mm (5.12 in) to 300 mm (11.81 in) depending on configuration.