Locking devices connect, or “lock,” power transmission components to rotating shafts. In this report, Motion System Design editors polled locking device experts for their advice on optimizing lifetime and ease of use. Here are the responses, which we believe you'll find most helpful.

What particular design/construction features in locking devices contribute to higher productivity, and why?

Mark/B-Loc: Keyless locking devices employ high-strength fasteners and alloy steels, which provide true zero-backlash power transmission connections. Most self-lock, making them durable in demanding motion control applications such as robotics, servo-driven timing pulleys, and indexing tables. They can be removed and reinstalled using only a torque wrench — allowing quick and easy access to mounted bearings, seals, and other wear parts. In precision-critical motion applications, keyless locking devices guarantee 100% repeatable accuracy for the equipment's life.

Doug/Zero-Max: Keyless shafts and single screw adjustment designs contribute to higher productivity. Mounted components such as hubs, gears, and sprockets rotate freely or rephrase on the shaft. A single-screw design provides quick, unlimited locking and unlocking of the bushing, saves time, and decreases component wear. Locking devices ensure proper balance and very little runout; their unique design also accommodates smaller-diameter shafts without keyways.

Andrew/Whittet-Higgins: Three design features contribute to higher productivity:

• One-piece mounting
• Torque/load measuring capabilities that ensure sufficient tightness
• Precise manufacturing for smooth contact with other components

Terry/U.S. Tsubaki: Keyless devices eliminate machining expenses, downtime, and maintenance because they easily slide into position. Cut keyways, splines, and grooves reduce shaft strength, since stress is concentrated at the cut. Therefore, a keyless device leaves the shaft intact and operates longer, especially in high-torque or hollow-shaft applications.

Slight discrepancies in fit cause backlash and fretting, which worsen over time and result in premature equipment failure. A keyless friction bond provides 360° shaft-hub contact and stays tight under shock and reversing loads.

Blair/Ruland: Most locking devices contain standard bore sizes and nonstandard hub requirements. Understanding that hubs are generally machined to match the locking device reduces rework and smoothes the development process. Minimum hub thickness is also critical and depends on locking device outer diameter and surface pressure. Hubs should be thicker than this calculated value to prevent excess stress and early failure.

Jeff/Lovejoy: Keyless locking devices offer a low-cost interference fit — optimum for high-torque, pulsating, or reversing load applications. This fit eliminates keys/keyways, fretting, corrosion, reduces replacements for damaged parts, curbs installation costs, and incorporates zero-backlash. Pre-assembly tolerances accommodate easy assembly or removal of mounted parts, without damaging the shaft or hub.

Eric/Fenner: Most keyless designs have two concentric rings with tapered faces drawn together through a threaded device. When pulled together, pressure builds inward on the inner ring and outward on the outer ring — locking the hub to the shaft. Machining a keyway takes significant time and weakens the shaft. During frequent start and stop applications and heavy vibrations, a wallowed bore and damaged key can result.

Keyless bushings can be positioned radially, allowing the teeth of each sheave to properly align with the teeth of the belt. Furthermore, a keyless locking device may be positioned along the length of a shaft, aligning both pulleys and sheaves for regular and synchronous drives. Improperly aligned sheaves cause premature belt failure and frequent downtimes.