Yes. Sentrimax rebuilds two- and three-stage planetary centrifuge gearboxes by replacing components worn beyond tolerance and re-machining salvageable parts back to OEM specifications. The rebuild verifies the original differential ratio is preserved, matches the gearbox to its backdrive type, and balances the reassembled unit with the rotating assembly to ISO G 0.5 before a test run.
What a planetary rebuild replaces versus re-machines
A planetary gearbox failure is rarely total. In most rebuilds, some components —
typically the gears with visible tooth wear or pitting, and bearings past their useful
clearance — are replaced with parts built to meet or exceed OEM specifications. Other
components, including shafts and housings without cracking or excessive wear, are
machined back to their original tolerance rather than replaced outright. Deciding which
path applies to which part is done during the inspection stage, before any repair work
starts, and is documented in the quotation package along with the scope of work and
required parts.
The goal is not simply to make the gearbox turn again — it is to restore the exact
differential ratio the centrifuge was designed around, since that ratio is what the bowl
and scroll speed relationship depends on for correct solids conveyance.
Two-stage vs three-stage: what changes in the rebuild
| Two-stage planetary | Three-stage planetary | |
|---|---|---|
| Reduction achieved by | A single planetary gear set | Two planetary gear sets working in series |
| Rebuild complexity | One gear set to inspect, machine and verify | Both stages must be inspected individually and matched to each other after repair |
| Where it’s typically found | Smaller and mid-size decanter and tricanter centrifuges | Applications needing a larger speed differential or higher torque capacity than one stage provides |
Whichever configuration is on your machine, both stages (or the single stage) go
through the same disassembly, oil analysis, and 75-point inspection process that applies
to the rest of the centrifuge, not an abbreviated version of it.
Verifying ratio and backdrive type before reassembly
Before a rebuilt planetary gearbox goes back into the centrifuge, two things are
confirmed: that the gear train reproduces the original differential ratio, and that the
gearbox is correctly matched to how the machine controls that differential — whether that
is a fixed mechanical ratio or, on some machines, a hydraulic backdrive working alongside
the gearbox rather than replacing it. Getting either wrong changes how the scroll conveys
solids relative to the bowl, which can show up as poor cake dryness or uneven wear on the
scroll flights long after the gearbox itself looks fine.
Reassembly is followed by dynamic balancing of the full rotating assembly to ISO G 0.5
and a test run — the gearbox is never verified in isolation from the components it
drives.
How a planetary gear set actually works
A planetary gearbox arranges gears around a common centerline: a central sun gear, a
set of planet gears that mesh with it and orbit around it, and an outer ring gear the
planets also mesh with. Depending on which of those three elements is held fixed and
which is driven, the arrangement produces a specific speed reduction between input and
output. A two-stage design uses one such arrangement; a three-stage design links two of
them in series, with the output of the first stage driving the input of the second, to
reach a reduction ratio a single stage cannot provide on its own. On a decanter, that
output ultimately sets the differential speed between bowl and scroll.
Precision fits: why machining accuracy matters more here than elsewhere
A planetary gear set only produces its intended ratio and runs smoothly if the
components are held to the tolerances they were designed around. A shaft that has worn
slightly undersized in a bearing bore, or a gear bore that has opened up a few thousandths
past its original fit, does not necessarily stop the gearbox from turning — but it
reintroduces play that shows up as backlash, uneven load sharing between planet gears,
and accelerated wear once the unit goes back into service. This is why measuring
critical precision fits is a defined step in the inspection stage, and why machining
salvageable components back to OEM tolerance is treated as a repair in its own right,
not a cosmetic cleanup before reassembly.
Parts sourcing when an exact replacement isn’t available
Replacement gears and bearings are sourced or built to meet or exceed OEM
specifications wherever possible. When an exact OEM part is not available — common on
older or discontinued gearbox models — Sentrimax’s engineering services and machine
shop can design and manufacture a reverse-engineered replacement, machined and
precision-ground to match the original component’s function and fit rather than leaving
a planetary gearbox unrepairable for lack of a stocked part.
When a planetary gearbox is beyond rebuild
If the housing is cracked through a structural section, or if wear has progressed to
the point that the original bore and shaft tolerances cannot be restored by machining,
rebuilding stops being the right recommendation. That determination is made at
inspection, and it is documented honestly rather than pursued as a repair that will not
hold up in service.
What a properly rebuilt planetary gearbox should feel like
After a rebuild, the input shaft should turn with the same resistance and the same
absence of play that a new unit would show — no perceptible backlash, no rough spots as
it rotates through a full turn, and consistent resistance whether turned clockwise or
counter-clockwise. Any of those being noticeably different from that baseline once the
gearbox is reassembled is a sign the rebuild has not fully corrected the underlying wear,
which is why the post-repair quality control inspection checks these characteristics
before the unit goes on to balancing and test run rather than assuming reassembly alone
means the job is complete.
How the machine shop supports a planetary rebuild
Much of what makes a planetary rebuild durable rather than a short-term fix happens in
the machine shop rather than at the assembly bench. Milling and lathe-turning bring worn
shafts and housings back to their original dimensions; precision-grinding restores gear
tooth surfaces and bearing seats to a finish that will not accelerate wear in the
replacement bearings and gears mated to them. This is the same engineering services and
machine shop capability Sentrimax applies across centrifuge repair generally, not a
separate gearbox-only process.
Documentation you receive with a rebuilt planetary gearbox
A rebuilt planetary gearbox does not come back with just a repaired part — it comes
back with the paperwork that shows what the repair actually consisted of. The
inspection report documents what was found at receipt, including the oil analysis
results and the measured precision fits that determined the scope. The quotation
package that follows lays out the parts, pricing structure and estimated delivery
before any work begins. Once the rebuild and balancing are complete, a post-repair
inspection and test run performance report confirm the finished unit runs correctly, and
the final invoice details all parts, labor and analyses performed. Together, this gives
a plant maintenance manager a record of exactly what changed inside the gearbox, not
just an assurance that it was “rebuilt.”
Related gearbox designs
Not every centrifuge uses a planetary design. If your unit shows the warning signs
covered on our gearbox failure signs
page but turns out to be a cycloidal drive instead, see our
CYCLO gearbox service page. If it uses a
hydraulic backdrive to set differential speed
rather than a fixed planetary ratio, that page covers what its service involves instead.
For the full range of gearbox repair options, see the
centrifuge gearbox repair overview.
What to do if the gearbox has already been opened by someone else
If a gearbox arrives having already been partially disassembled — by in-house staff
attempting a diagnosis, or by a prior repair attempt — that history does not disqualify
it from a proper rebuild, but it does need to be disclosed. Components that were
reinstalled without the correct precision measurement, or reassembled with mismatched
parts, can mask the original failure mode or introduce a new one. The inspection stage
accounts for this by measuring the gearbox as received, regardless of what work may have
already been attempted on it.
Why the rebuild-or-replace decision is made per component, not for the whole unit
It is tempting to think of a planetary gearbox rebuild as a single decision — rebuild
or replace the whole unit. In practice, the decision is made component by component
during inspection. A housing in good condition with a worn gear set is a different
scope than a housing with cracking and gears that are otherwise serviceable. Treating
the whole gearbox as one binary choice either overpays for a full replacement when
individual components would do, or risks reassembling a gearbox around a housing that
will not hold tolerance. The itemized inspection report exists specifically to avoid
both outcomes.
Send a gearbox in for inspection
An inspection at receipt tells you definitively whether your planetary gearbox is a
rebuild candidate and what the scope of that rebuild looks like before any repair work is
approved.
Frequently asked questions
How do you tell a two-stage planetary gearbox from a three-stage one?
The nameplate or original equipment documentation typically identifies the configuration. If that information is unavailable, our technicians identify the stage count during disassembly and inspection, since the internal gear arrangement differs visibly between the two.
Will a rebuilt planetary gearbox have the exact same ratio as the original?
Yes — restoring the original differential ratio is a specific verification step in the rebuild, not an assumption. The gear train is measured against the original specification before the gearbox is reassembled and returned to service.
Can only the worn gears be replaced, leaving the rest of the gearbox as is?
The inspection identifies which specific components are worn beyond a serviceable tolerance versus which can be machined back to specification. Only the parts that need it are replaced; the rest of the assembly is restored rather than swapped out unnecessarily.
Does a planetary gearbox rebuild require removing the gearbox from the centrifuge?
Yes. A full rebuild requires disassembly, precision measurement and machine-shop work that can only be done with the gearbox at one of Sentrimax's facilities, not on site with the unit still installed.
What causes a planetary gearbox to wear unevenly between its stages?
Uneven wear between stages can result from a misalignment introduced elsewhere in the drive train, contamination reaching one stage before the other, or a load imbalance from an issue with the bowl or scroll. The inspection looks at both stages independently to identify the cause rather than assuming it is symmetrical.
Talk to a centrifuge specialist
Send us the machine details and we will come back with an inspection scope and a quote.