Flex Couplings Technical Brief

Flex Couplings Technical Brief
Ron Giovannone
December 8, 2015

Jacks used alone or in multiple arrangements require couplings to transmit power to the input shaft. Nook Industries provides several types of couplings for use with jacks. Specifically, the three types of couplings offered by Nook Industries are Jaw Type Series, Heavy Duty Series (Gear style coupling), and Economy Series (Gear style coupling). When properly considering critical speed and torsional twist, multiple jack arrangement can be a preferred and economical method for providing linear movement.

Jaw Type Series

The jaw style couplings are a common coupling option for close mounted arrangements, or in arrangements where the radial loads are being supported through the proper placement of pillow block support bearings. Jaw style couplings are made of two steel hubs and a flexible polymer insert. The standard insert for the jaw style coupling is made from a polymer material that has a hardness of 98 Sh A. The maximum angular displacement is 0.9° and the maximum radial displacement is ± 0.09mm (±0.004").


An example would be a direct coupling of a motor or gearbox to an adaptor flange mounted on the jack, or when mounting line shafting which is supported with radial support pillow block bearings mounted close to the couplings.


However, it is possible to use jaw couplings without pillow block support bearings if the input is hand driven. Deflection of the link shaft still needs to be considered with respect to the ratio of diameter to length.


Heavy Duty Series

The heavy duty couplings have been standard options for many jack arrangement applications. They provide a rigid mount that can eliminate the need for pillow block support bearings, while at the same time allow for significant torque transmission through the system. They are available in both Full Flex and Flex Rigid. The flex rigid hub has a longer engagement with the outer sleeve then the full flex hub. The full flex style coupling allows for greater misalignment then the flex rigid, however the flex rigid provides greater radial support and can be considered as a radial support. The maximum angular displacement is 0.5° and the maximum radial displacement is ± 0.13mm (±0.005").

If using flex type couplings, full-flex couplings should be used for close coupled arrangements. For floating shaft applications, use two Flex-Rigid couplings. The rigid half should be mounted on the floating shaft.


Both the hub gears and outer sleeve are made from alloy steel providing a high degree of support and torsional strength.


Economy Series

The economy couplings have been added to the Nook Industries product line has an alternative the more expensive heavy duty series. They are only available in Full Flex style and have a reduced maximum torque rating as compared to the heavy duty series. The hub gears are made from alloy steel and the outer sleeve is made of carbon fiber material. In applications where the torque requirements are not significant and consideration has been made with reference to radial supports, the economy coupling series can be a good choice.

When using the economy series coupling it is recommended to always use a supporting pillow block bearing. In a close mount arrangement, radial supports may not be needed based on operating conditions. The maximum angular displacement is 1° and the maximum radial displacement is ± 0.30mm (±0.012").


Figure 1