Spindle gearboxes: role, architectures and maintenance
Between the motor and the spindle, the gearbox widens the usable power range: high torque for steel and titanium, high speed for finishing aluminium. Brochexpress works on motor-gearbox-spindle assemblies, on machines of every brand.
Why put a gearbox between the motor and the spindle
TLDR: A spindle motor cannot deliver high torque at low speed and high speed for finishing at the same time. The two-speed gearbox removes that compromise by giving the same machine two ratios.
Machining steel or titanium calls for torque at moderate speed. Finishing aluminium calls for the opposite: little torque, many revolutions. A motor on its own has to be sized for one or the other, which condemns the machine to excel on one family of materials and struggle on the other. The spindle gearbox removes that compromise: fitted in line between a water-cooled motor and the spindle, it offers a low ratio at high torque and a high ratio at high speed, selectable during production. That is what allows a single machining centre to handle parts with opposing cutting requirements without changing machine.
Hollow shaft planetary gearboxes and kit design
TLDR: Modern spindle gearboxes are hollow shaft planetary units: the shaft passes through their centre, which keeps them compact. So-called kit designs remove the redundant bearings between motor, gearbox and spindle, to the benefit of temperature, vibration and noise.
The dominant architecture is the hollow shaft planetary gearbox, whose central bore lets the spindle shaft pass through — a decisive space constraint on a machine tool, where every millimetre saved on the outer diameter is a millimetre available elsewhere. Recent generations improve torque density while reducing the outer diameter and increasing the bore diameter. Kit design, meanwhile, removes the redundant bearings from the system: instead of the motor, the gearbox and the spindle each carrying their own guidance, the assembly shares the same supports. The result is fewer parasitic stresses, and therefore lower temperatures, vibration and noise levels — and a longer service life for the spindle itself.
What we take on
- Hollow shaft planetary gearboxes fitted in line on a spindle
- Two-speed architectures, with selectable high torque and high speed ratios
- Motor-gearbox-spindle assemblies of kit design, without redundant bearings
- Spindle gearboxes on machine tools of every brand, including the REDEX ranges
- Output torques commonly encountered from 500 to 1,000 Nm depending on the configuration
How we approach the motor-gearbox-spindle assembly
TLDR: A gearbox cannot be diagnosed in isolation. The backlash it develops and the heat it produces are passed to the spindle shaft, and shorten the life of its bearings.
Diagnostics of the whole assembly
- Inspection of gear backlash, temperatures and vibration across the complete chain, motor and spindle included
Controlled removal
- Method established before work begins according to the architecture: on kit designs, the subassembly comes out without dismantling the whole machine
Overhaul
- Bearing and seal replacement, gear inspection, reassembly to the manufacturer's original clearances
Load test
- Verification of both ratios, of the shift between them and of thermal behaviour before return
Frequently asked questions
What is a gearbox for on a machine tool spindle?
It widens the motor's usable range: a low ratio delivers the torque needed for steel or titanium, a high ratio delivers the speed needed to finish aluminium. Without a gearbox, the choice between the two has to be made when the machine is designed.
Can a failing gearbox damage the spindle itself?
Yes. A gearbox developing backlash or running hot passes vibration and stress to the spindle shaft, which accelerates wear on its bearings. That is why we diagnose the whole motor-gearbox-spindle assembly rather than the suspected component alone.
Do you work on in-line two-speed gearboxes?
Yes. These architectures, fitted between a water-cooled motor and the spindle, require careful dismantling: we handle them together with the assembly they belong to.
What output torques do you encounter on this equipment?
Common spindle gearboxes deliver 500 to 1,000 Nm at the output depending on the configuration, but the exact figure depends on the model and the host machine.
Does the machine have to be dismantled to work on the gearbox?
It depends on the architecture. On kit designs, the subassembly can be removed without dismantling the whole machine. We establish the method during diagnostics, before any commitment.
A spindle gearbox to diagnose?
Gear noise, difficult ratio changes, abnormal heating: these symptoms spread to the spindle if they are left to settle in. Diagnosing the whole assembly tells you what actually needs overhauling.
Our teams are at your disposal from our sites in Beaurepaire (France) and Lussery-Villars (Switzerland) for a diagnosis or a personalised quotation.
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