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Modified couplings prove their worth in diamond polishing machine

27th May 2021
When a UK diamond toolmaking machine manufacturer needed a custom coupling for use on its line of new extreme material finishing machines, it turned to Huco for a precision solution. Huco was able to meet the requirements by modifying a membrane-type coupling with special bore sizes and keyways, and ship it to the OEM cost-effectively in the relatively small quantities required.

The machine manufacturer is a leading supplier of specialised, individually built, high-precision equipment to the polycrystalline diamond industry and to the single crystal diamond and gemstone industry. With customers across the globe, the company exports over 90% of its machines, meeting the needs of users who need to precision polish, grind and shape some of the world’s hardest and most extreme materials.

One of the company’s key product ranges is its planetary scaife benches, used to polish facets on single crystal diamond tools or for gem diamond polishing. These benches combine the high speed of rotation of a scaife plate with a relatively slow, smooth, horizontal planetary motion. This motion gives a number of advantages over a standard scaife. The plate does not become tracked as polishing takes place over an annular band, so the scaife surface remains smooth and flat. In addition, the motion results in a constantly changing angle of attack, with an action that produces line-free facets without the need for any manual finishing.

In a new design of planetary scaife bench, the company required a coupling for the servo motors controlling the XY axis during polishing, with specific but unusual bore sizes of 1.5” with a 1/8” keyway on one bore, and 14mm with no keyway on the other. Given that the highest levels of reliability and precision were essential, the company turned to Huco. It knew of Huco’s reputation for highly reliable couplings, and the two had enjoyed several previous successful collaborations.

Cost-effective modification

With over 40 years’ experience to call on, Huco offers machine builders access to a convenient and responsive customisation service that encompasses its complete range of standard couplings. A brand of Altra Industrial Motion Corp., a leading global supplier of power transmission equipment, Huco can offer cost-effective modification and customisation on any of the products in its extensive range, even when only relatively small batches are required.

Offering an in-house design and manufacturing capability, Huco has built a reputation for being able to provide customised couplings with a wide range of specifications on short lead times. The company can complete the design process in days, with average sized orders manufactured and delivered in a couple of weeks.

Working closely with the customer’s technical team, Huco engineers selected the Flex M bolted series membrane-type coupling as the best fit for the planetary scaife bench application. These couplings feature heat treated, spring-quality, stainless steel, thin pressed membranes – torque is resolved to simple tensile stresses in opposing segments of the membranes. The couplings have near-infinite life and a dynamically balanced construction which makes them suitable for applications requiring high rotational speed and motion integrity.

A two-stage version was chosen for its short envelope and low bearing load, as well as the ability to accommodate up to 2 degrees of angular misalignment. Huco was readily able to modify the coupling to provide the required bores and keyways, in a 47.9 mm long design with a peak torque rating of 11.3 Nm.

While a relatively small order such as this with an appreciable level of customisation might have been a challenge for other coupling manufacturers given the deadlines and target price, Huco’s lean, rapid-changeover production capability made it possible to manufacture the small batch of custom couplings as required.

Huco Managing Director, David Lockett, comments: “Customised precision couplings are vital for many builders of specialist equipment like planetary scaife benches. The coupling must offer not only the requisite performance for the application, but also meet the integration requirements. An off-the-shelf coupling will frequently not offer the specialisation required, so a customised component is often the best option.”

For the customer, the experience of working once again with Huco reaffirmed its excellent reputation for price and on-time delivery. As well as meeting the design specifications in a cost-effectively customised product, the modified Flex-M couplings have also proven extremely reliable, with the machine manufacturer reporting no field issues despite the highly demanding nature of the application.


Image 1: The Flex M bolted series membrane-type coupling was the best fit for the planetary scaife bench application.

Image 2: The company required a coupling for the servo motors controlling the XY axis during polishing, with specific but unusual bore sizes of 1.5” with a 1/8” keyway on one bore, and 14mm with no keyway on the other. (Image Source: AdobeStock_307118232)

About Huco

With more than 50 years of innovation, Huco Dynatork is recognised as a world leader in precision coupling and piston air motor technologies. Backed by extensive application experience, utilising the most advanced materials, Huco Dynatork designs and manufactures innovative power transmission solutions that meet the most demanding customer requirements.
Huco Dynatork manufactures a comprehensive range of precision coupling types including beam, Oldham, Uni-Lat, bellows, rigid, flex membrane, jaw and double loop. A full line of highly efficient piston air motors and air motor/worm gearbox assemblies is also offered.
Reliable Huco Dynatork products can be found in a variety of key markets including food processing, energy, textiles, medical, packaging, metals, machine tools and material handling on applications such as stepper & servo drives, dynamometers, scanners, pumps, fans & blowers, mixers, conveyors and compressors.

Editorial Contact: Brittany Kennan

Tel: +44 (0)1905 917477



Address: Progress House, Midland Road, Worcester, Worcestershire, WR5 1AQ, United Kingdom

Reader Contact:

Huco Direct: David Brooksbank

Tel: 001 815-389-6227



Address: 300 Granite Street, Suite 201, Braintree, MA 02184, USA