KRPXng rack & pinion drives concept, by REDEX

KRPXng is the newest range in the REDEX rack & pinion drives portfolio, designed for machine-tools with moving column or gantry. The cost-effective and easy-to-implement KRPX is an example of the close cooperation between REDEX and Machine-tools OEMs leaders.

Made of two planetary reducers, the KRPX-TwinDRIVE arrangement allows mounting on both sides of the machine frame. Coupled with an electrical preload, this system enables true zero backlash for rack and pinion applications while offering exceptional stiffness. Radial rigidity (accounting for up to 60 per cent of overall stiffness) is provided by the output shafted pinion technology invented by REDEX. This new version is now available in all sizes and integrates the new HQ-GF technology, which enables reduced energy consumption.

The implementation of a TwinDRIVE on a moving column or gantry machine was, before KRPX, rather difficult and required either a special extension on both sides of the main frame, or a new design and the production of special bracket supports to be fitted to the frame. Each option must keep the global stiffness at the same level as the main frame, to avoid deterioration of the dynamic performances. Such configurations required spending time and money on designing the part to fit, and manufacturing it. It may also significantly increase the design risk.

KRPX eliminates the need to design and integrate any high-precision fixation extension to the main machine frame, as the frame extension is already a part of the KRPX design itself. This simplifies the implementation process and is more cost effective (15 to 20 per cent less expensive) than conventional approaches. A precise keyway is machined on the mounting surface, allowing an easy settling while keeping mounting geometry. This smart system was specifically designed to cancel the risk of wrong mounting and system deflection.

Available in the five standard universal sizes (size 1 to size 5), KRPXng is compact and holds an implementation advantage with a pinion height not higher than 75.9-135mm. With this exclusive Racks & Pinion Drive concept, the machine-tools designer can expect to exceed the market standard with a maximum feed capacity up to 145,000N and stiffness on the rack up to 463,000N/mm. The full range is designed to be supplied together with the highest standard of quality racks, and its compatible fully automatic lube system.

KRPX housing is made of high-quality spheroidal graphite cast iron. KRPX uses oversized screws to ensure perfect mounting and absolute security. Its global structure has been optimised with FEM analysis methods to avoid deflection during acceleration. The output pinion is machined into the output shaft, and at the same diameter, offering a combination of transmissible torque and rigidity at the rack. The output bearing consists out of two preloaded and substantially oversized angular contact roller bearings.

Reduced radial bending

This construction enables the bearing to support the pinion as close as possible to the force, as only the thickness of the fastening nut separates the pinion from the output bearing. This design reduces radial bending, a factor responsible for up to 60 per cent of the overall distortion.

As a consequence, the natural frequencies of the global axis drive systems, in which the KRPX is integrated, can be raised more: its performance in terms of compound stiffness combined with its low inertia enables higher accelerations (up to 25m/s2), resulting in the ability to move heavier loads at higher speed.

KRPXng is a complete, ready-to-use product which is described as the most cost-effective improved dynamic precision combination on the market.

REDEX engineers have also introduced a new gear-finishing technology to the machine tool industry. This new technology, HQ-GF, ensures high reversibility, significant noise reduction and a decrease of over 15 per cent of power losses, meaning that thousands of kWh can be saved over the lifetime of a machine. With the HQ-GF inside, the new KRPXng technology is joining the long line of REDEX's innovations designed specifically by its engineers team to improve the machine-tool industry.

For more information about REDEX rack & pinion drives including the KRPXng, please visit

Andantex Ltd

Rowley Drive

+44 (0)2476 307722

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