Mitsui Seiki J6CN

$400,000 - $550,000 Updated 2026-03-14

Key Specifications

X Travel

600 mm (23.6 in)

Y Travel

500 mm (19.7 in)

Z Travel

400 mm (15.7 in)

Spindle Taper

BT40

Tool Capacity

20 tools

Table Size

800 x 500 mm (31.5 x 19.7 in)

Overview

The Mitsui Seiki J6CN is a CNC jig borer that carries forward decades of precision boring heritage into a modern CNC platform. With 600 x 500 x 400 mm (23.6 x 19.7 x 15.7 in) X/Y/Z travel, it is the mid-range model in Mitsui Seiki's legendary jig borer line — machines that have been the final word in hole location accuracy for mold, die, and gauge makers since the 1960s. Positioning accuracy is specified at +/-1.0 micron, and this is a spec that Mitsui Seiki takes very seriously at acceptance.

The J6CN's construction begins with a heavily ribbed Meehanite cast iron base that is thermally aged and precision hand-scraped. The linear axes use precision-ground and hand-lapped box guideways that provide the vibration damping essential for boring operations where surface finish and geometric accuracy are measured in tenths. The spindle is a precision cartridge design running to 8,000 rpm with 7.5 kW (10 HP) of continuous power — this is not a high-speed machining center but rather a precision instrument designed for boring, reaming, and light milling operations.

The Fanuc 31i-B control with high-resolution scales provides nanometer-level position feedback. Glass scales on all axes are thermally compensated and read with interpolation to 0.01 micron resolution. The machine includes a precision rotary table as standard with indexing accuracy of +/-1 arc-second, enabling precise angular hole patterns and bore locations that define jig boring work.

The J6CN occupies a unique position in the market. While high-precision VMCs from Yasda and Makino have absorbed much of the traditional jig boring workload, there remain applications — gauge making, master tooling, aerospace bearing housings, and inspection fixture manufacturing — where the jig borer's purpose-built precision is still unmatched. Mitsui Seiki's J-series remains the standard by which precision boring machines are measured, and the J6CN with its modern CNC control brings that heritage to shops that can no longer afford to rely on manual jig borers and retiring operators.

Full Specifications

Parameter	Value
X-Axis Travel	600 mm (23.6 in)
Y-Axis Travel	500 mm (19.7 in)
Z-Axis Travel	400 mm (15.7 in)
Table Size	800 x 500 mm (31.5 x 19.7 in)
Max Table Load	800 kg (1,764 lb)
Spindle Speed	8,000 rpm
Spindle Taper	BT40
Spindle Motor	7.5 kW (10 HP) continuous
Positioning Accuracy	+/-1.0 um
Repeatability	+/-0.5 um
Scale Resolution	0.01 um (10 nanometers)
Rotary Table Accuracy	+/-1 arc-second
Rapid Traverse Rate	10 m/min (394 ipm)
Tool Capacity	20 tools
Guideway Type	Hand-scraped box guideways
CNC Control	Fanuc 31i-B with high-resolution scales
Machine Weight	6,500 kg (14,330 lb)
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Model	J6CN
Brand	MITSUI SEIKI
Type	Jig Borers
Table Size W38table Size L50	ControlCNC (FANUC 30I MA)
Table Size W38	Table Size-L50"
Table Size W	38"
Table Size L	50"
Cnc Control	CNC (FANUC 30I MA)
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Specifications sourced from machinetools.com — verified 2026-03-28

Strengths & Limitations

Strengths

Sub-micron positioning accuracy of +/-1.0 um makes the J6CN the gold standard for precision hole location work
Hand-scraped box guideways with hand-lapped surfaces provide unmatched vibration damping for boring operations
High-resolution glass scales with 0.01 um (10 nm) interpolation provide position feedback at the nanometer level
Precision rotary table with +/-1 arc-second accuracy enables exact angular positioning for complex bore patterns
Meehanite cast iron construction provides thermal stability and structural rigidity essential for sub-micron work
Modern CNC control replaces manual jig boring with automated precision, addressing the retirement of skilled jig bore operators

Limitations

8,000 rpm spindle speed and 7.5 kW power limit the machine to light cutting — this is a precision borer, not a machining center
10 m/min rapid traverse makes the J6CN one of the slowest machines in any shop for non-cutting moves
20-tool ATC is minimal for complex parts requiring many tools, though jig boring typically uses few tools per setup
Premium pricing of $400K-$550K for a machine with limited material removal capability requires specific accuracy-driven justification
Niche application range means the J6CN often sits idle unless the shop has consistent precision boring and gauging work

Best For

Gauge and master tooling manufacturers where hole location accuracy to +/-1.0 um is a contractual requirement Mold shops boring precision alignment pin holes, leader pin bushings, and dowel locations in mold bases Aerospace manufacturers producing precision bearing housings and critical bore locations in structural components Inspection fixture manufacturers building CMM fixtures and checking gauges that require reference-grade accuracy Shops replacing retiring manual jig bore operators with a CNC platform that maintains the same precision standards Any application where bore location, diameter, and geometric accuracy must be verified and certified to sub-micron tolerances

Frequently Asked Questions

01 What does a Mitsui Seiki J6CN cost?

New J6CN machines typically price between $400,000 and $550,000. Used Mitsui Seiki jig borers hold value well; older J-series CNC models from the 2000s-2010s trade in the $150,000-$300,000 range depending on condition and hours.

02 How does a CNC jig borer differ from a precision VMC?

A CNC jig borer like the J6CN is purpose-built for hole location accuracy, with features like sub-micron scales, ultra-precise rotary tables, and construction optimized for vibration-free boring. A precision VMC offers higher speeds and broader machining capability but typically cannot match the jig borer's hole location accuracy.

03 Is the J6CN still relevant when high-precision VMCs exist?

Yes. For ultimate hole location accuracy — gauge making, master tooling, aerospace bearing housings — the J6CN's purpose-built precision still surpasses even the best VMCs. Shops doing this work consistently find the dedicated jig borer outperforms multi-purpose machines on accuracy.

04 What kind of work justifies buying a J6CN?

Shops that build master gauges, precision mold bases, aerospace bearing housings, or inspection fixtures where bore location and geometry must be certified to +/-1.0 um. If your tolerance requirements allow +/-5 um or looser, a precision VMC is more cost-effective.

05 Can the J6CN do milling operations?

Yes, light milling is possible with the BT40 spindle and 7.5 kW motor. However, the J6CN is optimized for boring and reaming, not aggressive material removal. Most shops use it exclusively for precision boring, reaming, and finish operations.