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Machine brand
Grob Spindle Repair and Head Overhaul
We overhaul spindles and spindle heads from Grob universal machining centres. CNC Spindle Service is an independent workshop in Sankt Augustin, Germany; we are not authorised by Grob and not a Grob service partner. A spindle unit can be crated and shipped to us, or removed and refitted on site abroad by prior technical arrangement.
Scope
Grob spindle systems we work on
On a Grob G-series machine the motor spindle does not sit in a fixed column. It is carried in a swivelling head that provides two of the five axes, so the spindle and its mounting are one assembly in practice. A rebuild that ignores the head is only half the job: after the spindle goes back, the geometric relationship between spindle axis, swivel axis and the pallet has to be measured again.
Motor spindles from G-series heads
The rotor runs directly on the spindle shaft inside a fairly compact housing, so heat, winding damage and bearing wear are hard to separate from the outside. The unit is stripped, shaft and housing seats are measured, and the bearing set goes back with the preload the design calls for.
Swivelling head and A-axis assemblies
The head that carries the spindle rotates, and its own bearings, clamping and seals wear as well. Where a customer sends the complete head, the swivel bearings, the clamp and the rotary feedthroughs for coolant and air are inspected with the spindle rather than after it.
High-torque and high-speed variants
The same machine family is built with quite different spindles: high-speed units for aluminium structural parts, heavier low-speed units for cast iron and steel. Bearing arrangement, lubrication and balance requirements differ between them, so the rebuild follows the variant in front of us, not a house standard.
Spindles from production systems
Units reaching us also come from linked manufacturing systems, where the machine runs in shifts and a stopped spindle stops a line. These arrive worn evenly rather than crashed, and the useful question is which parts are near their limit, so we report the measured wear on all of them.
The exact configuration depends on the machine model and the year of manufacture. Two machines with the same model designation can carry different spindle units, so we confirm the build from your nameplate photograph before quoting.
Symptoms
Faults we see most often on Grob spindles
Noise and rising vibration
Vibration on a swivelling head can come from the spindle bearings or from play in the head itself. Both are checked, because replacing bearings on a head with worn swivel bearings solves little.
Overheating and thermal drift
Cooling on a compact motor spindle depends on a clear jacket circuit and correct preload. A unit that heats up in the first minutes usually points to preload or lubrication; slow drift more often to the cooling side.
Runout at the taper
HSK tapers on 5-axis heads take abuse from tool changes at angle. The taper is reground and runout corrected against the bearing journals; a bent shaft or damaged nose is reported before further work.
Tool clamping problems
Clamping problems show as tools pulling out or as poor finish after a change. Clamping force is measured, the collet set and springs renewed, and the unclamp cylinder and its air or oil feed checked.
Encoder and orientation faults
Orientation faults on these heads are sometimes the spindle encoder and sometimes the head's own rotary measuring system. We separate the two before opening anything, since the cure is quite different.
Coolant or grease ingress
Heads working at angle with heavy through-tool coolant lose seals eventually. Once emulsion is inside, bearings and winding are both at risk, and we report how far it has reached before quoting the rebuild.
Process
What a repair looks like
The spindle is logged in and inspected on arrival, then dismantled completely. We measure shaft and housing geometry, check the bearing seats, inspect windings and encoder, and photograph what we find. You receive a written quotation with the scope of work before anything is repaired. After the work is done the unit is dynamically balanced, run-in tested and shipped with a test report containing the measured values.
The individual operations — bearing replacement, rotor and stator rewinding, taper regrinding, drawbar and clamping repair, encoder work, seal and cooling circuit overhaul — are described on the services section of our homepage. On a Grob spindle they are usually combined into one rebuild rather than ordered separately.
What to send with your enquiry
- Photographs of the spindle nameplate and of the tool interface
- Machine model, spindle type and year of manufacture
- A short description of the symptoms and when they appear
- Any measurements you already have — runout, temperature, vibration, current draw
- Whether the machine is still assembled or the spindle is already removed
Removal should be carried out by qualified personnel following the machine documentation. If that is not possible on site, ask us about removal and refitting as part of an on-site visit.
Shipping and on-site service
Our workshop is in Germany and we have no branch, warehouse or permanent staff in other countries. Customers outside Germany send the spindle to us by freight forwarder; we inspect, repair, test and return it. On-site work — removal, installation, alignment and commissioning — is possible internationally, but only after the job has been agreed technically in advance, so that the right parts and instruments travel with the technician.
Questions
Grob spindle repair — frequently asked
Yes. The workshop takes spindles directly from the machine owner, and no dealer needs to be involved. We are independent, which also means we hold no Grob authorisation and are not a Grob service partner; we say that plainly rather than leaving it vague. Parts are sourced on the open bearing and seal market.
Units reaching us usually come from G-series universal machining centres, the G350 and G550 sizes in particular, and from linked production systems built around the same heads. That describes what we see rather than promising compatibility with a given model, so send the spindle type plate and we will confirm.
In most cases the head geometry should be checked again. Removing and refitting a spindle in a swivel head can shift the relationship between spindle axis and swivel axis, and on a 5-axis machine that shows up in the part rather than in the spindle. Alignment measurement on site is arranged separately, by prior technical arrangement.
Typically 5 to 10 working days from arrival, depending on parts availability and what the teardown reveals. That is an estimate, not a committed date; a binding date is only valid if confirmed in writing. If the complete head comes with the spindle, allow more time, since its bearings and seals are inspected too.
Finding the fault means stripping and measuring the unit, and that work is charged. Once it is done you receive a written quotation with the findings and the proposed repair, and repair work starts only after you accept it. If the spindle is not worth rebuilding, the report says so.
Send us the spindle details
Tell us the machine model, the spindle type and what the machine is doing wrong. We come back with an initial assessment and a written quote before any work begins.