How Linear Motion Components Impact CNC Machining Operations

The key considerations for linear motion components on a CNC machine are the type of machine and materials it will be machining. CNC machines that machine metal must keep chips out of the linear components to prevent damage. Images provided by Bosch Rexroth. 

Q: What are the key factors that shop owners need to consider when evaluating linear motion components for their CNC operations?

A: Shop owners should always begin with the basics: the type of machine that’s being used, the material that’s being machined and how it’s being machined. For example, linear motion components in waterjet cutting machines need some sort of chrome plating or steel to protect against rusting. With lasers, heat must be managed correctly to reduce wear and tear on components and the overall machine. If the machine is working with a wood-based product, the linear components need to keep sawdust out so they don’t get clogged. Likewise, when machining metal, chips need to be kept out of the linear components to prevent damage. Regardless of machine type or workpiece material, the quality of the components matters. Operators can opt for cheaper components that lead to a smaller front-end cost but will likely need to be replaced sooner and could disrupt operations.

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Q: How has linear technology advanced over the years to meet consumer demand, including in CNC machining applications?

A: Ball bearings and cylindrical screws have long served as the foundation for many of the linear components used in CNC milling, as has the rack-and-pinion design. More recently, flexible plates in the runner blocks have helped transition bearings from an unloaded to a loaded zone. This adds load capacity and brings vibrations down. Measuring the impact these components have can get down to the micron level now, and it’s dependent on the operator to identify how precise operations and technology need to be.

Additional recent developments include a circulation piece inside a ball nut, which provides more of a tangential lift-off compared to an instantaneous one. In rails, there are now water-cooled versions for high-end machines, which help reduce the expansion of the rail and maintain a high level of precision and accuracy.

A final example is a ball nut where the screw is stationary and the nut and motor move. This can be used in both wood and steel milling applications to enable faster speeds and machine tools that can operate multiple cutting tools on a single axis, making individual cuts at the same time on one axis.

Recent advances in linear motion technology for CNC machines include flexible plates in the runner blocks that help transition bearings from an unloaded to a loaded zone to bring vibrations down. Water-cooled rails reduce machine expansion and help maintain precision and accuracy.

Q: What types of protective measures exist on linear motion components regarding debris management?

A: Seals are critical in protecting linear motion components, and full-contact seals routinely provide the best results. Wire brush options are available, but they don’t have the coverage that full-contact seals offer.

Plating also plays a central role in protecting against debris. There are various types, such as the chrome plating mentioned above for waterjet milling, which helps against rust formation.

Other debris management solutions include pneumatics near the bit, which deliver consistent air flow, as well as lubricants such as oil blasting. Again, operators need to make sure the components they’re using can handle a constant inflow of these types of debris deterrents.

Q: How are digital design tools improving the selection, integration and long-term success of linear technology?

A: Digital design tools play a huge role in integrating linear components into CNC applications. Previously, when sizing tools or CAD file integration wasn’t available, the selection process was more cumbersome. It typically involved phone calls and a review of files on a CD or flash drive. There wasn’t constructive transparency that allowed for easy selection.

Now it’s more of a consultative process, and among the most productive are free, web-based sizing tools that don’t require a specific log-in, like Bosch Rexroth’s LinSelect and configurator tools. Operators are learning about these types of resources daily and, as a result, are having more of a hands-on role in selection, which expedites the overall speed to market for both suppliers and end-users.

Eric Falasco is the sales product manager for screws and bushing/shafting at Bosch Rexroth.

Q: What are the key data points CNC operators are tracking regarding how their linear motion components are performing, and how does that factor into their maintenance efforts?

A: The two main data points CNC operators are tracking are vibrations and lubrication, with the latter being managed either automatically or manually. These two factors will continue to become more digitalized processes as sensors are appearing in advanced linear solutions. Operators are not only tracking them in real-time but are increasingly exploring AI for preventative and predictive maintenance. The most successful CNC OEMs know the typical lifespan they’re getting out of their linear components and have strategically planned for any disruption in downtime by factoring in lead time for replacement components.

Q: How should shop owners weigh the importance of higher quality components that could last longer but are more expensive, compared to cheaper components that may need to be replaced faster?

A: This is the fundamental issue when considering linear components, and it can be translated into a more direct question for operators: What is the cost of machine downtime? If operations are impacted because components or machines need maintenance or replacement, how is that going to affect throughput goals or production metrics?

It’s important that CNC OEMs with purchasing departments have a clear dialogue on how purchasing decisions impact productivity. If the cheapest option for a component is chosen, what may seem like a difference of a couple of hundred dollars could end up affecting the operations on a much larger scale when the component eventually breaks down.