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A small but vocal discussion in the 3D printer community is on bearings and bushings that are used by 3D printers, and how these can be optimized to create better printers and better print quality. Some believe 3D printing will run counter to globalization by ensuring that end users will begin producing many of the products that they consume. Others think 3D printing could be the means through which manufacturing will be fundamentally transformed. Many in the printer community are intent on increasing the quality and the speed of 3D printing. This task involves refining all printer components to make them the best they can be, and this includes the bearings and bushings that make up the linear motion systems.
Why linear motion systems are important in 3D printing
In most 3D printers the build platform (including the extruder) slides over smooth rods as it moves. The polished rods support the components and guide the motion of the extruder along a linear path. Bearings or bushings are used on the straight steel rods to create motion that is smooth and jerk-free where the extruder is moving in a single direction.
Among 3D printer enthusiasts, bearing and bushing options are available, including bushings of various materials, and linear bearings, which tend to be made of bronze and have rows of ball bearings located on the inside.Bushings, or sleeve bearings, look like tubes and can be made from bronze or polymers. Both types attempt to achieve a reduction in power, noise and wear. The bronze bushings are sometimes impregnated with oil or require external lubrication for operation.
Bronze bushing enthusiasts appreciate the lower cost over
linear bearings in the application. Also, because they can
run on hardened or less expensive non-hardened shafts, the ancillary equipment tends to be less expensive.
However, bronze bushings have their detractors. Bronze bushings can wear away at the shaft, and they sometimes require significant amounts of lubrication at regular intervals. Additionally, the lubrication sometimes forms a gritty mixture that wears away at the shaft. Bronze bushings can also have a stick-slip problem, which results in a jerky motion when printing as the bushings are prone to sticking on the shaft followed by slipping over the shaft. They can also have large toler-ances,where they are not made to specification, and this can make them a poor fit for 3D printers.
Polymer bushings, which are another option for those interested in sleeve bearings, can be made from a range of materials. Slip-stick can also be a problem with cheaper polymers, as can the wide tolerances that sometimes accompany mass-produced bearings. Mass-produced polymer bearings are occasionally available in limited sizes, and may not meet the needs of the consumer.
High-end self-lubricating polymers tend to reduce the likelihood of slip-stick, especially where the coefficient of friction is low and the dynamic and the static coefficients of friction have values that are similar. With polymer bushing manufacturers, it may be possible to get the exact required tolerances and the precise sizes that are required.
Linear ball bearings are also in use and are the alternative to bronze and polymer bushings. They can also be tube-like, flanged or pillow boxes, but have linear ball bearings that are located along their inside diameter. These run on the shaft, making the motion a rolling one rather than a sliding one.
The cost of linear ball bearings can also vary significantly depending on quality. Durable well-known linear ball bearings can be expensive compared to bushings. In addition, they should be used with hardened shafts so that the balls do not eat into the shaft; the ancillary equipment asso-ciated with them can be expensive.
Some suggest that maintenance can be higher, and that lubrication needs to be monitored to ensure performance with linear ball bearings. Moreover, because dirt and dust can combine with greasing, these balls can eventually run louder and even jam if the grit-containing lubrication becomes a significant problem.
The issue of whether to choose bearings or bushings seems to be more pronounced among those with RipRap printers, which involve a high degree of innovation. The culture of this printer com-munity promotes individualization and adaptation. Essentially, users may replace all components according to preference or even make the components that are required themselves.
A view of the Vesconite Hilube bushings inside a 3D printer in a South African computer compo-nent.
For those converting their machines or those committed to modifications, the debate as to whether to use bearings or bushings is particularly pertinent. One option is to include specified parts that are described in production catalogues.
3D printer users report a phenomenon called dimpling and pimpling when a rod becomes deformed. This phenomenon is caused by the rod slightly lifting on one side and slightly tilting on the other side as the bushing or bearing moves from one side to the other. This is typically a result of wear to the rod. 3D printer users report that this phenomenon is eliminated when Vesconite Hilube bushings are introduced. Vesconite Hilube is a thermopolymer in the Vesconite range, designed for operating in wet conditions, including pump and marine applications.
The material is self-lubricating, requires no greasing, and the polymer bushings require very little maintenance. Because there is no gritty greasing mixture that embeds on the mating surface, wear caused by the constant movement of this contaminated oily mixture is eliminated. Wear caused by metal-on-metal contact also becomes a thing of the past, as the hard-wearing polymer glides smoothly over the rods.
Vesconite Hilube has an unlubricated friction coefficient on steel of 0.1 and a static friction coefficient as low as 0.08. These friction coefficients make the movement of the bushing along the rod smooth and also eliminates the problem of the jerky motion (stick slip) when the extruder is moved to a new location.
