A planetary gear set puts a sun gear, three or more planet gears and an internal ring gear on one axis. Load splits across the planets, so the same ratio fits in a much shorter housing. The carriers, pins and ring blanks that hold that stack together come off our machines.
Most planetary failures trace back to one of these four. Each one costs a rebuild.
If the carrier pin bores are not on a true pitch circle, one planet takes most of the torque. That planet wears first and the set starts to whine under load. Position error on the carrier, not gear tooth quality, is usually the root cause.
A pin that is 0.01 mm undersized lets the planet tilt. Tilt cuts the contact area on the tooth flank and raises local stress. The flank pits, then spalls.
An out-of-round ring forces the planets into a moving mesh clearance. Backlash changes with rotation angle, so the gearbox sounds different at different speeds. Buying a ground ring blank does not fix a housing that clamps it oval.
A thin carrier plate bends between the pins. Planet alignment shifts and the sun gear sees edge loading. This shows up in EV traction motors during hard launches, not on a bench at constant load.
One setup strategy per part family, checked against the ratio it has to hold.
The carrier is the part that sets planet spacing. Bore position tolerance drives how evenly the planets share load, so we keep all pin bores in one 5-axis setup instead of repositioning between holes. Position error stays inside ±0.005 mm on a 200 mm carrier.
For high-ratio sets we check the pitch circle against a CMM report before the part leaves the floor. The report lists each bore's radial position, not just hole diameter. That is the number that matters when the set is assembled.
Planet pins are turned and ground to a diameter tolerance that keeps the planet bearing preload steady. A pin held to ±0.005 mm on diameter and 0.005 mm on straightness keeps the planet from tilting under torque. Both ends get a chamfer so the bearing slides on without shaving material.
Internal ring gears start as a machined blank. We hold the bore round within 0.01 mm and keep wall thickness even, because an uneven wall distorts when the housing clamps it. Gear cutting and grinding are done after the blank is stress-relieved, so the roundness holds through heat treat.
Ratio and duty cycle decide the layout before any drawing is cut.
| Layout | Typical ratio per stage | Best for | Watch out for |
|---|---|---|---|
| Single stage, 3 planets | 3:1 to 8:1 | Compact servo reducers | Lower torque capacity per planet |
| Single stage, 4–5 planets | 3:1 to 6:1 | High-torque EV drives | Carrier must stay stiff between pins |
| Two stages compounded | 8:1 to 40:1 | Robot joints, winches | Stack-up error adds across stages |
| Ring fixed, carrier output | 3:1 to 10:1 | Wheel hub drives | Ring bore roundness is critical |
| Sun fixed, ring output | 2:1 to 6:1 | Backdriven actuators | Higher bearing loads on carrier |
Carrier plates, housings and covers with angled bores cut in one setup. 16 simultaneous 5-axis centers, up to 4,000 mm travel.
Sun shafts, planet pins and ring blanks turned to ±0.005 mm with Ra 0.2–0.8 μm on bearing surfaces.
Flat carriers, mounting flanges and internal gear pockets. 27 three-axis machines handle the simpler profiles at volume.
One-off carriers and housings for fit checks before tooling. Quotation and DFM analysis inside 12 hours.
Hardcoat anodizing for aluminium carriers, electroless nickel for steel pins, bead blasting for cosmetic covers.
Housings and covers where the load path does not need a machined billet. Machined interfaces stay on the CNC side.
| Item | Range | Notes |
|---|---|---|
| Maximum part size | 4,000 mm | Larger carriers split into bolted assemblies |
| Achievable tolerance | ±0.005 mm | ±0.0002 in, verified on CMM |
| Gear face finish | Ra 0.8–1.6 μm | Ra 0.2–0.8 μm on journals |
| Materials | Aluminium, steel, stainless, titanium, copper, plastics | 6061, 4140, 17-4PH, Ti-6Al-4V, PEEK |
| Batch size | One prototype to 10,000+ parts | No minimum order quantity |
| Inspection | 100% before shipment | Reports on request |
Founded in 2011, operating three wholly-owned plants across 7,600 m² in Dongguan and Singapore.
16 simultaneous 5-axis centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers.
The same tolerance on the first part and the thousandth, checked with in-process monitoring.
Raw material check, in-process monitoring and final inspection on every run.
A free design-for-manufacturing review comes back with the quotation. Production can start within 24 hours.
Prototype carriers and full gearbox housing runs on the same process flow.
Traction motor carriers need stiff pin plates that survive launch torque without flexing.
Two-stage reducers in robot joints live or die on backlash repeatability across a million cycles.
Actuator gear sets trade weight for stiffness, so titanium and 7075 carriers get thin walls.
Winch and indexer gearboxes run hot and dirty, so housings must hold bore alignment after heat cycles.
A standard train places gears on separate parallel shafts. A planetary set puts the sun, planets and ring on one axis, so input and output share a centerline and the housing gets shorter.
The tradeoff is the carrier. Every planet position depends on that one part, so carrier tolerance matters more than it does in a parallel-shaft box.
With the ring held fixed, the ratio is 1 plus ring teeth divided by sun teeth. A 60-tooth ring with a 20-tooth sun gives 4:1.
Change which member is fixed and the same hardware gives a different ratio. That is why the fixed member is called out on the drawing, not just the tooth counts.
Three planets is the usual starting point. It balances load, leaves room for a stiff carrier and keeps the assembly simple.
Four planets share load further and suit high-torque EV drives, but the carrier has less material between pins. Five or more only pays off when the ring is large enough to keep pin spacing practical.
Choose machined when pin bore position has to hold inside 0.02 mm, when wall sections are thin, or when the run is under a few thousand parts.
A casting makes sense for larger housings where the load path is less sensitive and tooling cost spreads over volume. We machine both, so the recommendation follows the tolerance, not the process we prefer.
Bearing journals want Ra 0.2–0.8 μm. Rougher surfaces wear the bearing race and change preload over time.
The pin body between the journals does not need that finish. Spending the cycle time only where the bearing sits keeps cost down.
We machine the ring blank and hold the bore round within 0.01 mm. Gear cutting and grinding follow stress relief so roundness survives heat treat.
If the ring is a purchased, already-cut part, we machine the housing to match its actual bore, measured rather than nominal.
A 2D drawing with tolerances, the material, and the quantity. For carriers, mark which bore is the datum. For pins, state the bearing fit class.
If the drawing is incomplete, the DFM review flags it. Quotation and that review come back within 12 hours.
Yes. Uploads stay confidential and an NDA is available on request before you send drawings.
Gearbox geometry is the kind of IP that competitors would like to see, so we treat drawings and CAD files as confidential by default.
Carriers, pins, sun shafts and ring blanks quoted with a free DFM review inside 12 hours. One prototype or ten thousand parts, same process control.
12-hour quote100% inspectionNo minimum order quantity
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Upload your 3D model or 2D drawing and get a quotation with a free DFM analysis. Maximum processing size 4,000 mm.
CNC Metals 13 grades
CNC Plastics 10 grades
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Surface & post-processing 10 options
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