Rotary Stroke Bearings
Rotary Stroke Bearings
FAQ Rotary Stroke Bearings
Q: Where can I get CAD data of the rotary stroke bearing components?
A: CAD files in STEP format are available from the Online Product Catalog. Choose a component. In the detail view under 'Download' you have the option to request the required files that will be sent to you by e-mail - easy access without registration. 
Q: What tolerance should be used when creating the locating bore for the guide bush?
A: The outside diameters dB of guide bush models N550, N552 and N553 are manufactured with ISO tolerance n4, and model N570 with ISO tolerance h6.
The guide bush can be damaged when it is pushed in. The locating bore should therefore be given a tolerance (e.g. n4/E6) that makes it unnecessary to push the guide bush in with force.
The guide bush can also be bonded in position. In this scenario, the locating bore must be large enough to provide an appropriate gap for the adhesive. The instructions of the adhesive manufacturer must be noted and complied with. It is best to use an adhesive which does not take too long to harden.
Q: What type of lubrication is suitable for a rotary stroke bearings?
A: In principle, greases and oils that are suitable for lubricating roller bearings are also suitable for rotary stroke bearings. The choice depends on the conditions of use (e.g. temperature, rotary speed, ambient media). Grease should be applied very sparingly. Solid lubricants are not suitable. Dry running is also possible in special instances.
Q: How often does a rotary stroke bearings need to be lubricated and/or maintained?
A: A MarMotion rotary stroke bearings that is large enough and is not subjected to abrasive particles or corrosion during operation, will show virtually no wear. Depending on the application conditions, life-long lubrication may also be possible or lubricant may be applied via existing central lubrication units. Maintenance can be performed at the usual intervals.
Q: What does preloading mean?

A: MarMotion rotary stroke bearings are preloaded, i.e. are absolutely free of play. The exact preloading value set is crucial for the running characteristics of the rotary stroke bearings. Low preloading enhances ease of movement. Higher preloading increases rigidity.
Even adjustments in the preloading of a few micrometers can produce a significant change in the characteristics of the rotary stroke bearings. Narrow production tolerances mean that components can be exchanged. It is best to always order complete rotary stroke bearings consisting of guide bush, ball cage and guide shaft, since the optimum preloading for the specific application can then be configured at the factory.

Q: What is the tolerance for the internal diameter of the guide bush?
A: The inside diameter of the guide bush and the diameter of the guide shaft machined to ISO tolerance h3 are dimensioned so as to generate a preloading in the rotary stroke bearing. If necessary, the diameter of the guide shaft and the inside diameter of the guide bush are matched to ensure optimum preloading. If ordered together, the rotary stroke bearings will be supplied as complete assemblies consisting of guide bush, ball cage and guide shaft.
Q: Are special designs possible?

A: All components can be supplied to customers´ specifications, e.g.:

Guide bush:

  • Special length and diameter
  • Grooves
  • Flange

Ball cage:

  • Special length and diameter
  • Other ball diameters or number of balls
  • Ball arrangement, e.g. in ball zones
  • Locking ring
  • Axial cages

Guide shaft:

  • Special length and diameter
  • Inner thread / outer thread
  • Flange
  • Hollow shaft
Q: Are stainless steel versions available?
A: Guide bushes, guide shafts and balls consist of hardened roller bearing steel 100Cr6 (1.3505). If required, stainless steel (e.g. 1.4112) is also possible as a special design. The balls in ball cage N502 are made of stainless steel as a matter of course.
Q: Are ceramic versions available?
A: If required, ball cages with ceramic balls can be supplied as special design.
Q: Are rotary stroke bearings available in aluminum or other materials?
A: Ball cages are made of brass or plastic (POM). Aluminum or bronze cages are also possible (special design).
Q: How can rotary stroke bearings be sealed against dirt and soiling?
A: Guide bush N553 is fitted with shaft sealing rings and model N570 with wiper seals. Alternatively, bellows can be used, e.g. leather bellows for model N820.
Q: How is the service life of a rotary stroke bearing calculated?

A: In the case of a MarMotion rotary stroke bearing of adequate size (P10 less than C10), the material is only loaded in the endurance limit. Provided the guide is free of abrasive particles and corrosion, the service life will be virtually unlimited.

Q: How is the bearing capacity of a rotary stroke bearing calculated?
A: The bearing load must be less than or equal to the bearing capacity of the rotary stroke bearing. For uniform radial loading, loading capacities of the ball cages are set out in the online catalog. The online product selector helps you to choose the components following the dimensions or loads given by your application. Intelligent filters guide you to the combination you need. In case of an unevenly distributed radial load or a moment load, the equivalent radial load must be calculated (see catalog).