Shaft couplings for precision applications

Where flexible shaft couplings are used on machines to transfer power and rotation, there are many different couplings to choose from.  There are also many different types of applications, each having a different set of performance requirements.  It is Important to match the performance needs of the application to the capabilities of the coupling specified.  Modern technology has pushed the envelope on machinery in-regards to the speed, power, and precision requirements.  With these changes, the need for coupling features like zero-backlash, high torsional stiffness, and low inertia factor in for positioning accuracy and performance under loaded conditions on the machinery.

Servomotors, steppers motors, precision gearboxes, ball-screws, and linear actuators are examples of components used in these high-performance applications requiring the highest levels of precision.  Examples of applications requiring high precision would include high-speed pick-and-place applications for placing chips into integrated circuit boards, high-speed indexing operations on packaging equipment, ball-screws, gantry systems, among others.

The CD coupling from Zero-Max has zero-backlash, high torsional stiffness, clamp-style hubs for reliable and secure shaft connection, whether keyed or keyless, and high misalignment capacity.

Zero-backlash and high torsional stiffness

Both backlash and torsional stiffness affect the amount of “lost motion” between the driving and driven shafts.  Zero-backlash and high torsional stiffness are important for precision applications to maintain accuracy in aggressive motion profiles and high speeds.  High torsional stiffness is important to minimize any torsional windup so the coupling does not experience lost motion under dynamic load conditions, and also to minimize settling time when indexing or stopping a high inertia load.  Figure 1 shows an application where the CD coupling is driving a turntable with an indexing motion.  The high inertia of the turntable could cause a “bounce” when stopping the index motion; however, the torsional stiffness of the CD coupling minimizes that bounce and reduces settling time at the end of the index cycle, meaning more production throughput for the machine.

shaft couplings fr precision applications
Figure 1 – An application where the CD coupling is driving a turntable with an indexing motion

Shaft connection

The method of shaft connection can also affect the performance of the coupling.  If for example a setscrew connection comes loose, the resulting lost motion will affect the positioning accuracy and overall performance of the system similar to how backlash would.  Zero-Max offers clamp-style hubs with clamp collars of their own design for higher strength and clamping forces compared to commercially available collars. Figure 2 shows the breakout of features for Zero-Max stainless-steel clamp collars, and these same features apply to our standard collars used on our steel and aluminum clamp-style hubs.  The high strength, oversized construction of the collars yields high clamping forces for a strong, secure shaft connection that will hold up to demanding applications having high acceleration/deceleration, starting, stopping, indexing, and reversing.  The secure shaft connection ensures high performance for the CD coupling for reliable long-term use without any maintenance.

shaft couplings for precision applications
Figure 2 – Features for Zero-Max stainless-steel clamp collar

Misalignment capacity

Although precision applications tend to have well aligned shafts, misalignment can still be a factor.  Shafts will always have some inevitable misalignment and additional misalignments can be introduced due to machine bases settling, component wear, or deflections occurring under high torque loads. 

The open-arm design of the CD coupling disc pack, along with the composite material used, allow the CD coupling to provide up to 3˚ angular misalignment, while eliminating fretting corrosion that can shorten the lifetime of metal disc-style couplings.  That compares to many other disc-style couplings that offer only 1˚ or 1 ½ ˚angular misalignment.  The parallel and axial misalignment ratings also benefit from increased misalignment capacity with the open-arm design of the composite disc pack.  This can increase the life of those components and the system (figure 3).

Figure 3 – The open-arm design of the CD coupling disc pack, allow the CD coupling to provide up to 3˚ angular misalignment

Indexing, start and stop applications

Precision Couplings are required for demanding applications for accuracy with rapid start/stop cycles.  A typical indexing applications is a high-speed horizontal form-fill-seal machine, also known as a pouching machine.  The CD Coupling used here drives a set of indexing rolls that pull the pouch through the form, fill, and sealing operations needed to package the product.  In use, this machine sees indexing rates of up to 3x per second, and the CD Coupling holds up very nicely to this punishing, high indexing rate involving starts/stops at 3-times per second.

Reaction loads / Sideloads

Depending on the coupling chosen, precision couplings having high torque and torsional stiffness are often less forgiving to handle misalignment due to their stiffness.  They can have higher reaction loads imparted to the connected components, which can affect lifetime and performance of the system.  The unique design of the Zero-Max field-proven composite disc-pack also reduces the reaction loads on the coupled components caused by this misalignment, but still maintain zero-backlash and high torsional stiffness.  Minimizing the reaction loads is important to extend lifetime for the coupling and the connected components, while also allowing for optimum performance of the machine (figure 4).

Figure 4 – The unique design of the Zero-Max field-proven composite disc-pack reduces the reaction loads on the coupled components caused by this misalignment

Torque transducer / Test machinery applications

Torque transducer applications are good examples of applications where low reaction loads are beneficial.  Torque transducers have only limited radial load capacity, so low reaction loads are vitally important, not only for the transducer, but for minimizing stress in the test machine.  Lower stress means more accurate readings for the testing, as you eliminate the influence of reaction loads and stress. 

Figure 5 – Transducer is supported by Single-Flex CD couplings by Zero-Max

Zero-Backlash and high torsional Stiffness are also important for these applications. Torque transducers can be “fixed” mounted to the machine frame using Double-Flex CD couplings,  “floating” where the transducer is supported by Single-Flex CD couplings, or can be a “flange-type” wireless transducer.  Zero-Max CD couplings can be configured to work with any of these styles of transducers, and Zero-Max Engineering is always available to assist with sizing and selection for the application (figure 5).


Many applications will have unique performance requirements, dimensional challenges, or other requirements that require customization to meet the specific needs of the application.  Zero-Max offers customization services and decades of field-proven results to fit the specific application needs. 

Figure 6 – Zero-Max offers customization services and decades of field-proven results to fit the specific application needs

Whether it is enhanced torsional stiffness, a design to overcome dimensional fit issues (especially common in retrofit applications), different plating or coating to hold up to a challenging environment, or higher speed capacity, Zero-Max is up to the challenge.  Zero-Max has dynamic balancing available for higher speed or vibration-sensitive applications.  Custom designs are available from a 1-piece quantity to hundreds or more, with no up-front engineering costs.  It is free to inquire and get a quote if you have a need for a custom coupling.  Zero-Max Engineering has decades of experience to assist with designs for challenging applications.

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