About Mitsui Seiki

Factory Tour

Our main factory in Kawajima, Japan, built in 2001, is truly the world’s premier facility for precision machine tool production. All facets were carefully considered and designed for the utmost in precision manufacturing for our “mother” jig boring machines. Consider these attributes:



  • The cement pilings in the floor are more than 30 meters (100+ ft.) deep, right down to the earth’s bedrock.
  • The floors are 1.2 meters (4 ft.) thick in critical areas and 1 meter (3.28 ft.) thick elsewhere
  • The temperature is controlled, floor to ceiling, at 20°C, ±0.5° (68°F, ±0.9°)
  • The humidity is controlled, floor to ceiling, at 55%, ±0.5%
  • The air throughout the factory is exchanged 24 times per hour
Take this brief tour of the factory’s hallmarks that elaborate on these points:

Laminar Flow Air Conditioning System that Minimizes Temperature Changes
This A/C system first sends cooled, dried air above the sub-ceiling. From there it is introduced into the room towards the floor through multi-hole plates that cover the ceiling. The air is collected at floor level, and recirculated via return ducts. This method has the following features:

1. There are virtually no temperature differences for any location in the volume of the manufacturing room. Precision will remain stable even when machining, or assembling large machines, and there will be no restrictions on machine layouts.

2. There will be almost no air flow close to the floor so there will be no influence from pressure changes, allowing for precise laser positioning & geometry measurement.

Foundation to the Bedrock
When creating mother machines, changes in the foundation level and vibrations from external sources must be addressed. Our factory foundation is constructed on 1,700 piles that are driven down to the bedrock. The floor is a minimum of 1meter thick layer of concrete. Further, the building’s structural foundation is entirely separate from the machine assembly area foundation, so that any potential vibrations from outside sources, such as overhead cranes’ movements, does not affect the machines precision adjustments.

Even slight temperature changes within the factory can negatively impact machine accuracy. Therefore, Mitsui Seiki has taken the utmost care to prevent inaccuracy by minimizing the need to move machines from place to place. Additionally, the isolated, temperature controlled shipping area is positioned adjacent to the assembly area. Moreover, the temperature of the machines in the shipping area is gradually adjusted to the outside temperature, which prevents condensation from forming, even on hot, humid summer days.

Machine Assembly Area
The Machine Assembly Hall area has four sections, each serviced by multiple overhead cranes. Here, the assembly of vertical, horizontal and 5-axis machining centers, jig boring machines, jig-grinding machines, screw grinding machines and specialized machines takes place. As the machines never change location during this process, this area is also used for hand scraping, collective assembly, accuracy adjustment, inspection, customer acceptance testing, and shipping coordination.

Component Assembly Area
Assembly of spindles, workheads, rotary tables, ballscrews, and other critical sub-assemblies is carried out in the Component Assembly area. These specialized rooms are located in the same building, just adjacent to the Main Assembly Hall to minimize movement to the final assembly location. This area is monitored very closely. There is also a room for conducting spindle head adjustments after assembly if necessary.

Small Machine Processing Area
Also in the same building, and adjacent to the Main Assembly Hall is the Small Machine Processing area, where finish-machining touches are carried out on parts that make up the core aspects of our machine tools. Items such as spindles, tables, ball screws and other critical parts are processed using the latest quality oriented methods.. The jig boring and thread grinding equipment in this area can produce finish-machining tolerances of 0.001mm or better. The location of this workshop affords minimum movement from machining to the respective sub-assembly room.

Large Machine Processing Area
Again, in the same building as the Main Assembly Hall, is the Large Machine Processing area. Here, large cast parts such as beds, columns, tables and saddles are machined. This area is equipped with massive machine tools, including Mitsui Seiki’s own HS8A, high precision horizontal machining center.


Precision Measurement Area
To make machines that are capable of performing in the 1µm area, we require the tools and technology that can measure even better than 1µm. Of all of the rooms in the factory, the Precision Measurement area has the strictest temperature control, maintaining a temperature of 20°C ± 0.1°C. This area is equipped with Mitsui Seiki's laser-lead measuring instruments, three-dimensional measuring instruments, roundness measuring instruments, surface roughness measuring instruments, and universal microscopes.

Development and Design
The fundamental thinking behind our machine development and design is first and foremost ultra precision. New concepts are evaluated by a team of very experienced and highly trained engineers. Once a new product concept or design is accepted, structural analyses are carried out using the latest in finite element methods (FEM) to ensure that beds and columns have maximum rigidity, and that there will be no bending from any individual component weight, or planned machining forces. In parallel, sub-systems, and peripheral devices and components are designed and analyzed for suitability to the intended applications. CAD-CAM systems are employed thought the engineering process to facilitate all aspects of design, manufacturing, and communication. Mitsui Seiki’s approach to this critical stage of the machine tool’s evolution allows us to continuously respect the customers’ wishes and requirements. Each solution is engineered for the end user using many common components, and attributes. See also “Common Attributes” in our web site.