Technical Selection Guide
Foot Mount, Flange Mount, or Hollow Shaft: Choosing the Right Planetary Gearbox Mounting Configuration
The planetary gearbox mounting configuration determines how the unit transfers its reaction torque to the machine frame — and choosing the wrong one adds brackets, misalignment risk, and maintenance complexity that could have been avoided entirely at the specification stage.
Most OEM machine designers and procurement engineers focus on the torque rating and gear ratio when selecting a planetary gearbox — and reach the mounting configuration decision last, almost as an afterthought. This is the wrong order of operations. The mounting configuration determines the mechanical interface between the gearbox and the machine structure; changing it mid-project requires structural redesign of the mounting points and sometimes the motor position. Selecting it correctly at the concept stage eliminates a category of engineering problems entirely.
There are five primary planetary gearbox output shaft options encountered across industrial and mobile equipment applications: foot mount with solid output shaft, flange mount with solid output shaft, hollow shaft (shrink disc), splined hollow shaft, and torque arm. Each solves a different physical installation problem, and each has failure modes associated with incorrect application. This guide maps all five to the applications where they perform correctly.
The Five Mounting Configurations — When Each One Is Correct
AFoot Mount — Solid Output Shaft
Best for: base-plate mounted conveyor drives, pump drives, mixer drives
The foot mounted planetary gearbox is the simplest configuration: the gearbox housing has integral mounting feet that bolt directly to the machine base plate or floor mounting frame. The reaction torque is transferred through the feet into the structure. The output shaft connects to the driven machine via a coupling (jaw, gear, disc, or rigid type).
Where it fails: When the coupling alignment is not maintained at installation. A 0.1 mm parallel misalignment between the gearbox output shaft and the driven shaft creates a radial force on the output shaft bearing that is not within the gearbox’s design load. Over 2,000–4,000 hours this causes premature output shaft bearing failure — typically misdiagnosed as a gearbox quality problem. Laser-align all foot-mounted installations. Retorque mounting bolts at 200-hour run-in.
Key Data
Alignment: Laser required
Coupling: Flexible recommended
Torque path: Feet → base plate
Maintenance: Retorque at 200h
Typical use: Conveyors, mixers, pumps
BFlange Mount — Solid or Splined Output
Best for: motor-facing configurations, vertical installations, confined spaces
The flange mounted planetary gearbox bolts its housing flange directly to the mounting face of the motor or driven machine — no separate base plate or foot mounting structure required. This is the most space-efficient configuration and is standard for agricultural hydraulic motor drives (sprayer wheel drives, slurry spreader drives) and for compact industrial installations where the gearbox is co-located with the drive motor.
Critical point: The flange pilot diameter must be machined to the correct tolerance — typically H7 for the housing and h6 for the motor flange pilot. An undersized pilot bore causes housing offset that creates misalignment at the input shaft; an oversized pilot bore allows the gearbox to shift position under shock loading. Request the pilot bore tolerance specification from the supplier and verify it matches the motor flange before installation.
Key Data
Pilot tolerance: H7/h6 standard
Bolt pattern: Must match motor
Torque path: Flange → motor frame
Space saving: ★★★★★
Typical use: Hydraulic motor drives, vertical shaft drives
CHollow Shaft (Shrink Disc) — Most Common for Industrial Drives
Best for: conveyor head drives, mixer agitators, rotating drum drives — no coupling required
Most Widely Used
The hollow shaft planetary gearbox eliminates the coupling entirely by mounting the gearbox output bore directly onto the driven shaft. The driven shaft passes through the hollow output bore and is clamped by a shrink disc (or taper bushing) that creates a friction-based torque connection. The reaction torque is taken through a torque arm attached to the gearbox housing.
This is by far the most widely used configuration for industrial conveyor drives, agitator drives, and drum drives because it eliminates: shaft alignment errors, coupling wear and replacement, and the axial space required by a coupling. Installation time is reduced by approximately 60% compared to a coupled foot-mount unit of equivalent torque.
Critical installation step: The shrink disc must be tightened to the manufacturer’s torque specification using a calibrated torque wrench — not an impact driver. Under-torqued shrink discs slip at peak torque events and cause fretting corrosion on the driven shaft bore. Over-torqued shrink discs distort the hollow output shaft bore and cause bearing misload. Both failure modes are preventable with a torque wrench and a 15-minute installation procedure.
Key Data
No coupling: Yes — direct shaft mount
Torque path: Shrink disc → driven shaft
Reaction: Torque arm → frame
Install time vs. foot: −60%
Typical use: Conveyors, agitators, drum drives
Used where the driven shaft reverses direction under load at high frequency (winch drives, slewing drives, traversing drives). The spline transmits torque in both directions equally without the fretting that occurs at smooth-bore shrink disc interfaces under repeated reversal. The spline requires lubrication with MoS₂ grease at every assembly or removal event.
Typical applications: Hydraulic motor winch drives · Excavator track drives · Slewing machinery where reversal >50 cycles/hour
ETorque Arm (Swing-Mount)
Used in combination with hollow shaft or flange mount where no rigid mounting structure is available near the driven shaft. The gearbox “floats” on the driven shaft, with a single torque arm connecting the housing to a fixed structural point. The torque arm must be mounted at exactly 90° to the housing centreline for correct load distribution; incorrect torque arm angle transfers bending load into the housing mounting bore.
Typical applications: Conveyor tail drums · Belt scrapers · Portable drive units on mobile machinery
Quick Selection Guide — 3 Questions to the Right Configuration
If you are unsure which mounting configuration is correct for your application, work through these three questions in order:
Q1: Is there a driven shaft that the gearbox output can mount onto directly?
YES → Hollow shaft (shrink disc or splined) is the correct configuration. Eliminates coupling, alignment risk, and coupling maintenance. NO → Proceed to Q2.
Q2: Is the gearbox bolting directly to a motor flange, or is there a separate base structure?
MOTOR FLANGE → Flange mount. Compact, no base required, direct motor interface. BASE STRUCTURE → Proceed to Q3.
Q3: Is the installation environment accessible for periodic laser realignment checks?
YES (accessible) → Foot mount with flexible coupling. Most familiar to maintenance teams, easiest to service. NO (confined, elevated, remote) → Flange mount or hollow shaft — these eliminate the periodic alignment requirement.
Our inline planetary gearbox series is available in all five mounting configurations across 16 frame sizes from 1,000 to 500,000 Nm. The NB300R right angle planetary gearbox is available in foot mount and flange mount configurations with solid output shaft, covering right-angle applications requiring a 90° change in shaft direction alongside the standard torque reduction.
Not Sure Which Configuration? Send Your Application Details — We Recommend and Quote in 24 Hours
Torque, ratio, application, motor interface type, and any dimensional constraints. We select the correct mounting configuration, frame size, and output shaft specification — and return a dimensional drawing plus quotation within 24 hours. MOQ 1 unit.
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📧 [email protected] · Canada Planetary Gear Drive Co., Ltd
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Common Installation Errors by Configuration Type — and How to Prevent Each One
Each mounting configuration has a characteristic installation error that accounts for the majority of early post-installation failures. Knowing these errors in advance eliminates the most common avoidable failure modes:
- Foot mount: Misalignment at initial installation, not rechecked after thermal settling. The motor-gearbox coupling goes into resonance when thermal expansion shifts the alignment out of tolerance at operating temperature. Solution: laser align at installation; re-check at 200 hours running temperature.
- Flange mount: Incorrect pilot bore fit — either too tight (forcing the gearbox housing out of concentricity) or too loose (allowing housing shift under shock loading). Solution: verify the pilot bore tolerance specification against the motor flange drawing before installation, not after the gearbox is already on site.
- Hollow shaft / shrink disc: Under-torqued shrink disc that allows slippage at first peak torque event. Slippage polishes the driven shaft surface, making re-clamping at correct torque insufficient — the polished surface no longer provides adequate friction. Solution: torque to specification with a calibrated wrench; confirm the driven shaft diameter is within tolerance (typically h6).
- Splined hollow shaft: Assembly without MoS₂ grease on the spline, causing fretting corrosion within the first 500 reversal cycles. Solution: apply MoS₂ grease to both male and female spline surfaces at every assembly event — never assemble dry.
- Torque arm: Torque arm installed at an angle other than 90° to the gearbox housing centreline, transferring a bending load into the housing mounting bore rather than a pure torque reaction. Solution: confirm the torque arm pivot pin is parallel to the gearbox output shaft before final tightening.
These five errors account for an estimated 70% of all post-installation failures that are incorrectly attributed to product quality. In every case, the gearbox is undamaged and would have performed correctly if installation had followed the correct procedure. A supplier who provides installation instructions — not just a data sheet — reduces the probability of these errors occurring. All units in our range are supplied with installation documentation covering the specific mounting configuration ordered.
