An Introduction to Trunnion Rotary Table

Posted on Feb 9, 2021

Trunnion Rotary Table

The trunnion rotary table is designed to provide additional 2 axes to the 3-axis machine tools and increase the positional accuracy, which is a very compact yet rigid accessory for modern CNC machining centers.

What Is a Trunnion Rotary Table Used for?

The trunnion rotary table is designed to provide additional 2 axes to the 3-axis machine tools and increase the positional accuracy, which is a very compact yet rigid accessory for modern CNC machining centers. The trunnion rotary table is typically made from heavy-duty cast iron, providing maximum rigidity and quick rotation that is free of backlash. The rotary device is also simply called the trunnion table. It is available for accurate machining operations like milling and drilling, which is suitable for medium to large applications.

Similar to the 4th axis rotary table, which is added on the vertical machining center, in general, the tilting axes of the trunnion rotary table upgrades the capability of cutting multiple sides of the intricate part simultaneously, the positional accuracy, the repeatability, and also productivity with a full 360° rotation. The trunnion rotary table can be available with work-holding devices like machine vises, chucks, sub-plates, and also spacers. As for the power source and control system of this work holding table, there are manual, pneumatic, hydraulic and also computerized types in the market.

The trunnion rotary table offers rotational axes for various CNC machining centers and enhances the productivity and surface properties of the intricate machining applications. These features make the table a demanding accessory for machine tools used in aerospace, shipbuilding, automotive industry and many more.

3+2 Axes Structure of Machining Center

Different from the integrated 5 axis machining center, adding the high-performance rotary positioning technology, the trunnion rotary table can achieve the 5-axis machining operations with less cost and simple installation, expanding the available work of the general 3-axis machine tools. The structure is considered as the “3+2 axes machining”. 

The trunnion table upgrades the machining center by adding the rotational axes, or tilting axes, to the original three linear axes, which are known as the X-axis, Y-axis, and Z-axis. The X-axis on a machining center is the linear direction where the column travels along, which is typically the left-to-right direction in a VMC. The Y-axis is aligned with the path the workpiece moves along from front to back. The Z-axis is typically aligned with the main axis of the machine tool; it is vertical in a VMC. 

A trunnion rotary is responsible for offering the rotational axes around the X-axis and the Z-axis, achieving the 3+2 machining technology and high-end accuracy and productivity of the CNC machines. However, before adding the trunnion rotary table to your CNC machines, you should check if the CNC system of the 3-axis machine can accommodate the controlling of simultaneous 4- or 5-axis machining operations.

On the other hand, the 5-axis machines that have integrated trunnion table or rotary work holding tools are also advantageous to ensure simultaneous 5-axis machining with a simpler setup. Although the acquisition cost of the 5-axis CNC machines is much higher than adding the trunnion rotary table, they still have their advantages. 

For example, the 5-axis machine allows cutting tools that have standard lengths, reducing the costs relative to tool turnover and insert replacement, increasing the feed speed. Also, the high accuracy of the 5-axis machining operations results in fewer scraps as well as less waste. The easier setup can reduce the time and effort of the user and human interference of the complex process.

:: Read more: What Are 4th and 5th Axis CNC Rotary Tables?

Working Principle of Trunnion Rotary Table

In the turning or milling machine, whether the spindle with the cutting tools is locked or not, the rotating trunnion rotary table is used to turn the symmetrically round parts under a predetermined high speed. The workpieces are mostly large aerospace, energy industry components, or other medium to heavy-duty applications. Some CNC machines that leveraged the two rotational axes at once, which adds tilting movement to spin, can let the tools get further closer to the surfaces of the parts. The trunnion table offers a stable plane for heavy workpieces to rest. 

There are twin points of connection between the trunnion rotary tables. The trunnion tables in the market typically feature easy installation and flexible options with a mounting vise and other work holding tools. In general machining centers with trunnion tables, similar to the linear axes, the drives and electric motors driving the rotational axes are mounted outside the tooling area. 

The open working area translates the power to a large range of movement for the trunnion rotary table, providing fully 360° rotation. The wider the range of the movement of the trunnion table, the easier it is to operate the jobs, permitting much more high performance and rapid turning or milling of intricate contours. To provide high speed and high turning force during mill-turn operations, the trunnion rotary table used in the mill-turn machines will require drives that supply higher torque such as a 4,000-Nm torque drive to complete the tasks.

Why Do You Need a Trunnion Rotary Table?

For starters, since the trunnion rotary table provides exceptional rigidity and flexibility for the machining center with the extra rotary motion, the machines can allow shorter and more hard cutters, which are produced with aggressive parameters. 

These tooling options can upgrade the surface finishes, tool life and also reduce the cycle time. As for the trunnion table itself, it typically has heavily ribbed cast iron construction, making the rotary table durable and rigid to bear the vibrations and repeated operations in long-term use.

When it comes to the simple setups and installation, the trunnion tables in the metalworking environment are designed to be flexible, which can be simply bolted onto a wide range of CNC machines, allowing the user to cut on multiple sides of the parts for mid-range productions. The fast setups and ease of operations for precise 5-axis turning, milling, drilling and other machining tasks of the trunnion rotary table provide the solution to significantly upgrade the productivity of the shop in a short time.

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