Miniature single-taper, flange-type locking assembly with small timing pulley.

Gears, belts, and motors may be the workhorses of industry, but without locking devices, they wouldn’t accomplish a thing. Locking devices make multi-component solutions possible, holding almost any power transmission element on any shaft and letting it go when necessary.

Today, because of intense pressure to maximize uptime, precision, and efficiency while minimizing material, machining, and operating costs, keyless frictional locking devices are the hot trend. Although conventional keyless devices — now decades old — remain viable, the new breed of frictional types are clearly the future.

The old way

The goal of any motion control system is to repeat a specific move or move sequence many times without deviation. Timing belts and pulleys are frequently used to achieve such predictable precision because they are highly accurate as well as efficient.

Standard methods of mounting timing pulleys on shafts, such as keys, setscrews, taper-lock and QD bushings, reduce efficiency by introducing unwanted backlash into the system. And, if the pulley or other drive element is subjected to reversing or intermittent loads, backlash will worsen with time. Ultimately, you can count on a steady loss of accuracy and eventual connection failure.

As accuracy deteriorates, it may be necessary to adjust the system to restore the original timing of all indexed components. This process can be quite time consuming and is fraught with errors.

Another drawback to traditional technology is that it requires expensive machining. Keyways may need to be broached or milled, holes drilled and tapped, and tapers machined into drive components. Though partially offset by the efficiencies of mass production, the resources required to complete these manufacturing steps represent a hidden cost with standard solutions.

Go keyless

In light of the shortcomings associated with standard locking technology, keyless locking devices offer an attractive solution — a true zero-backlash, permanent yet fully adjustable connection that requires no complicated machining of the drive element.

Keyless locking devices come in several sizes and styles.

Keyless locking devices connect components by means of a mechanical interference fit. Torque, thrust, and other loads are transmitted through frictional resistance generated by pressure applied simultaneously to the shaft and mounted component. Contact pressures easily exceed those achieved through traditional interference fits.

The resulting connection is entirely backlash-free, eliminating the problems inherent in keyed connections; micro-movement, fretting corrosion, impact loads, and loss of accuracy are of no concern here. In fact, assuming proper selection and installation, a keyless locking device connection should never fail.

Keyless locking devices also can be made quite small; they’ll even fit on thin-walled drive elements using a single taper to maximize concentricity. Any shaft you might find in a newer motion control system is fair game.

Because a key is not required to transmit torque, system components such as shafts and bearings don’t need to be as large — smaller parts, lower costs. Likewise, timing pulleys and other drive elements need only a straight-through bore, saving more time and money.

As for advantages of ownership, keyless locking devices can dramatically shorten maintenance cycles because they can be relaxed quickly and easily to original fit clearances. This can add up to a huge savings in terms of downtime when it comes to mounted components requiring periodic timing adjustments or removal.

How they work

Keyless locking devices work according to the wedge principle. Integrated high-strength steel rings with one or more tapered interfaces convert standard screw-clamp loads into radial contact pressure. In the case of internal devices, the pressure is applied between the shaft and component bore. With external devices, the pressure is applied around the drive component’s hub.

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