Cooling options for rack and pinion drives

Machine Tools How Drives Stay Cool with High Dynamics

2025-09-24 From Redex | Translated by AI 4 min Reading Time

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If you want to make machine tools more productive through higher feed rates and greater dynamics, you need to dissipate or compensate for the heat generated. Redex offers cooling-optimized and cooled rack and pinion drives and gearboxes for these purposes.

To maintain the precision of the machine tool at higher torques and speeds, heat must be dissipated from the drive train.(Image: Redex) — To maintain the precision of the machine tool at higher torques and speeds, heat must be dissipated from the drive train.
(Image: Redex)

Not long ago, milling tables were limited to the production of prismatic parts with drilling and/or threading operations, whose round shapes were created through low-speed milling. Today, a multitasking machining center can produce cylindrical parts through high-speed turning and milling/drilling on the same machine—in a single setup—immediately boosting productivity. The only catch is that at too high speeds and torques, the resulting heat can lead to inaccuracies in machining.

Cooled motors and gearboxes are available for multitasking machine tools with high continuous speeds.(Image: Redex) — Cooled motors and gearboxes are available for multitasking machine tools with high continuous speeds.
(Image: Redex)

The development of an outstanding multi-purpose machine tool requires adjustments in the drive type and machine structure to combine power, versatility, and precision. Technological changes are necessary for this.

Motor manufacturers already offer air- or water-cooled versions of motors that enable high continuous rotation speeds at acceptable operating temperatures. In this context, Redex has developed cooling options for its gearboxes over recent years. This way, heat is dissipated, and an operating temperature is maintained that aligns with the precision expected by the end user from a multitasking machine.

Possible Drive Solutions for Machine Tools

When selecting a suitable drive solution for linear movements for a new machine tool, three options are available:

Direct drive (linear motor)
Ball screw drive
Rack and pinion drive

Linear motors have become largely unaffordable due to the cost of magnetic elements, cables and additional cooling components. The high power consumption compared to servo motors also makes this option unattractive.

Although ball screws are widely used in the general machine tool market, they also have disadvantages when installed in multitasking machines: for example, heat build-up after repeated and intensive movement of the ball screw leads to positioning errors due to thermal expansion. This undesirable effect could affect the ability of the machine tool structure to pass the ISO 230-3:2020-6 tests for thermal deformation.

Taking these factors into account, rack and pinion drives prove to be a good solution for controlling the thermal behavior of feed drives in large multi-purpose machines. Redex has developed cooling-optimized rack and pinion drives for highly dynamic and heavy-duty movements.

Advantages of Cooling-Optimized Rack and Pinion Drives

With cooled rack and pinion drives, there is no need to compensate for thermally induced changes in length when controlling the linear movement.(Image: Redex) — With cooled rack and pinion drives, there is no need to compensate for thermally induced changes in length when controlling the linear movement.
(Image: Redex)

Cooling-optimized rack and pinion drives are characterized by a low temperature at the contact point between the pinion and rack, regardless of the feed speed. In addition, there is no critical speed at high feed speeds, as the rack and pinion mesh at low speeds. Another practical feature is the modular and freely extendable travel length using rack segments, as well as the high and constant rigidity regardless of the position.

Cooled rack and pinion drives allow for easier control of the linear motion of a machine tool without the need to compensate for thermally induced length changes that can sometimes occur when using a ball screw or uncooled rack and pinion drive.

Keep Cool Under Pressure

The manufacturer has developed several cooling options to protect the drive from heat buildup when used in high-dynamic machine tools, such as multitasking models.

The company draws on its experience: About 40 years ago, it developed water-cooled, two-stage gearboxes for high-torque high-speed spindle drives in machine tools. It was the first manufacturer to offer cooled hollow shaft gearboxes to achieve a satisfactory operating temperature in the integration between the motor and the spindle. This gearbox maintained an operating temperature delta (Delta T) that was about 10 °C lower than that of the spindle and motor, even at speeds of up to 12,000 RPM.

In the latest development, the work of the engineering department focused on the newest generation of gearbox motors. Both the motor and the gearbox have been equipped with a cooling circuit to dissipate heat. This system ensures a low operating temperature. As a result, the spindle structure remains stable, which is necessary for precise turning and milling operations.

Predicting the Operating Temperature of Gearboxes

The rated power of planetary gearboxes is derived from the theoretical bearing and gear load capacities as a function of the load level at different speeds and the calculated service life. Redex engineers have developed a numerical model that can be used to predict the operating temperature of gearboxes and, in particular, their thermal behavior and efficiency. This model makes it possible to extrapolate a torque curve corresponding to the constant (thermal) power of the system in a given configuration. A test program with the RP series planetary gearboxes showed the correlation between theoretical and experimental data.

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With this approach, the company predicts and evaluates the thermal operating limits in order to propose the optimal solution for heat dissipation and determine the most suitable cooling method.

Details of the RP Gearbox Series

The RP planetary gearbox series offers two cooling options: Standard and special configuration. The standard configuration is a form of external forced lubrication in which cooling is achieved by recirculating the lubricating oil bath in a closed circuit, allowing losses to be dissipated via an oil/water or oil/air exchanger.

Redex offers a choice of forced lubrication or a cooling jacket as cooling options for the RP gearbox series.(Image: Redex) — Redex offers a choice of forced lubrication or a cooling jacket as cooling options for the RP gearbox series.
(Image: Redex)

As a distinguishing feature from competitors, Redex offers holes as standard in both the SRP and KRP series gearboxes as well as those in the KRPX series, which facilitate the internal circulation of the coolant.

If the requirements of an application exceed the thermal capacity of a drive, the standard cooling option for RP series drives is a suitable option. For cooling drives on large multi-purpose machine tools, this is the simplest and most cost-effective solution from this manufacturer.

In the special versions, a cooling jacket is used instead of the external forced lubrication. The additional cooling jacket increases the size, weight and cost of the standard gearbox, but can be very effective for certain applications.

Application Tests with Temperature Control and Digital Twin

The company often develops and produces application-specific solutions for machine tool manufacturers. It tests these, including running tests with full temperature control and checking the nominal data of the gearbox. To support accurate simulations, the manufacturer has developed modeling systems that use digital twins.