KA Series Single Standard Worm Gear Reducer

The KA Series Single Standard Worm Gear Reducer — designated WPKA — is the hollow-bore output variant within the WPA dimensional family. Rather than presenting a solid output shaft stub, the WPKA output bore passes completely through the worm wheel hub, accepting the driven shaft directly. This shaft-mount arrangement eliminates the output coupling, coupling guard, and key-fit alignment procedure that solid-shaft reducers require, replacing them with a single keyed bore and a locking element. The result is a compact worm gearbox that sits directly on the driven machine shaft — shorter in the output direction, lighter in total assembly weight, and simpler to maintain than any comparable solid-shaft configuration. Covering sizes 50 through 200 with standard gear ratios of 10:1 to 60:1, the WPKA suits every application where the driven shaft can act as the reducer’s mounting point rather than a downstream connection target.

Technical Specifications — KA Series (WPKA) Hollow Bore Worm Reducer

The Hollow Bore Advantage: What Disappears When You Remove the Output Shaft

The engineering case for hollow bore output is straightforward: every component between a solid-shaft reducer’s output stub and the driven shaft is a potential failure point. The WPKA eliminates the output coupling, coupling guard, and the requirement for parallel and angular alignment at the driven end. The driven shaft slides directly into the bore and is secured by a DIN 6885 parallel key and a locking element — the entire output connection is inside the reducer housing.

Output Bore Engineering: Fit, Key, and Locking Element Selection

Bore Fit and Tolerance

The WPKA output bore is machined to H7 tolerance — a close clearance fit that centres the driven shaft within 0.015–0.025 mm radial clearance depending on bore diameter. This tolerance is tight enough to prevent rocking of the reducer on the shaft under dynamic loads, while still allowing manual disassembly without pressing equipment. The mating driven shaft should be machined to h6 or js6 tolerance at the bore contact length. For shafts machined to k6 (light interference), a hydraulic push-out tool will be required at disassembly — acceptable in permanent installations where removal is infrequent.

Keyway and Torque Transmission

The output bore keyway is broached to DIN 6885 Form A at the W×Y dimensions listed in the specification table. A parallel key seated in matching keyways on both bore and driven shaft transmits the output torque. For reversing or shock-load applications, a second key 180° opposite (keyed rather than single-keyed bore) can be specified as a custom option, increasing the torsional capacity of the shaft-bore connection without increasing the bore diameter. The key is a standard item; it must be fitted to zero backlash in the shaft keyway before the reducer is slid onto the shaft — a rocking key that contacts only on one face causes fretting corrosion in the bore over time.

Locking Elements and Shrink Disc Options

Three locking element options are available for the WPKA bore connection. A set screw through the bore hub is the standard, lowest-cost option — adequate for unidirectional constant-torque loads. For reversing or cyclic torque, a proprietary locking ring (shrink disc) that generates radial clamping force over the full bore length provides superior axial retention and eliminates the fretting risk associated with set screws under reversed loading. For hollow shafts or shafts where set screw indentation is unacceptable, a keyless interference bushing can be pressed into the bore and expanded onto the shaft — this option requires no machined keyway in the driven shaft.

Where Hollow Bore Output Solves Real Australian Engineering Constraints

The WPKA is most valuable where the driven shaft diameter, position, or axial length makes a solid-shaft reducer with coupling arrangement geometrically awkward. The following application archetypes represent its strongest fit:

• ⛓️ Conveyor Head Shaft Drive — Shaft-Mount Configuration
  A WPKA slides directly onto the conveyor head shaft, secured by a torque arm to the conveyor frame. The worm reducer, motor, and all drive components sit on the conveyor shaft — the structure carries zero drive weight. Repositioning the reducer along the shaft to adjust sprocket position requires no structural modification. Size 80–120 at 20:1–40:1 covers the majority of Australian food processing and materials-handling conveyor applications.
• 🌾 Grain Auger and Screw Conveyor Head Drive
  Grain auger shafts in Australian bulk handling are typically 40–60 mm diameter and extend to the edge of the loading hopper — a solid-shaft reducer and coupling would require the motor to overhang the hopper, creating a cleaning and safety access problem. A WPKA bore-mounted directly on the auger shaft brings the motor parallel to the screw axis and eliminates the overhang entirely. Size 100–135 at 30:1–50:1 covers the standard 540 rpm PTO-equivalent electric motor speed range for bulk grain augers.
• 🚿 Irrigation Channel Gate and Rack Actuators
  Headstock-mounted gate actuators in Australian irrigation infrastructure use WPKA units where the gate shaft must be the mounting reference. The reducer sits directly on the gate lift shaft; a torque arm anchors the housing to the headstock frame. Salt-water spray environments on coastal irrigation infrastructure benefit from the WPKA’s sealed housing with no exposed coupling gap for moisture entry.
• 🎡 Carousel and Turntable Centre-Shaft Drives
  Rotating display units, product turntables, and carousel drives in Australian retail and exhibition environments use WPKA size 50–70 at 40:1–60:1 directly on the vertical centre shaft. The self-locking property at these ratios holds the turntable position when power is removed — preventing drift under uneven display loading — without any additional brake device.
• 🔄 Fan and Blower Shaft Drives (Low-Speed Retrofit)
  Where an existing large-diameter fan or blower shaft must be driven at very low speed (10–30 rpm output) from a standard 4-pole motor, a WPKA at 60:1 bore-mounted directly on the fan shaft eliminates the design challenge of supporting a solid-shaft reducer at the cantilevered end of a large-diameter shaft. The hollow bore centres itself on the shaft and the torque arm takes the reaction.
• 🏗️ Winch and Hoist Drum Shaft Drives
  Wire rope winches on Australian lifting equipment use WPKA size 120–155 at 20:1–40:1 mounted directly on the drum shaft. The worm self-locking provides the secondary load-holding function required by Australian Standards AS 1418 for manually suspended loads — with the hollow bore placing the reducer directly at the drum shaft, the drive envelope is minimised in the drum width direction.

PTO Shaft Integration, Torque Arm Configuration, and Drive Accessories

The WPKA input shaft is a standard WPA-class solid stub, accepting any standard motor or PTO coupling. The distinctive accessory requirements are on the output side — the hollow bore and torque arm combination replaces everything that a solid-shaft reducer’s output coupling system would require:

Shaft-Mount Installation: Step-by-Step for Reliable Service Life

WPKA Selection: When Hollow Bore Is the Right Answer and When It Isn’t

The hollow bore configuration is not universally superior to solid-shaft. The WPKA is the correct choice when the driven shaft meets the following criteria — and a standard WPA or WPS is the correct choice when it does not:

Maintenance Schedule — WPKA Hollow Bore Configuration

For bore size confirmation, torque arm design assistance, and shrink disc selection for WPKA applications across Australia, the technical team at our worm gearbox engineering portal provides application-specific calculations and dimensional drawings. For agricultural shaft-mount drive integration including PTO-to-electric conversion projects, contact us via the technical enquiry page with your driven shaft specification.

Frequently Asked Questions — KA Series (WPKA) Hollow Bore Worm Reducer