Rotary Stroke Bearings

Rotary Stroke Bearings
Important notes on design
EN

As already described, preloading value v represents an important criterion for the functioning of the MarMotion high-precision rotary stroke bearing. It influences the loading capacity, the smooth running and, if the recommended values are exceeded, the service life.

The following installation notes should therefore be observed:

  • Load the rotary stroke bearing more with radial force than with moments in order to prevent local overloading of the balls.
  • In the case of high moments, arrange two guide zones one after the other with a gap in between.
  • If necessary, fit a joint support tube with screw-on flange.
  • Set the points of application of the driving force in the guide plane if possible.
  • Protect from impact. Impacts can leave ball impressions even on hardened running faces.
 

Rotary Stroke Bearings
Mounting the guide bush
EN

Avoid pressing the guide bush!

Avoid pressing the guide bushes as this may damage the micro-finished guide diameter d1. The bush adapts to the location bore. This results in form errors and excessive preloading, thereby impairing the correct functioning of the rotary stroke bearing. Clamp-type fittings and pressure screws are also unsuitable for the same reasons.

The tolerance of outside diameter dB of the MarMotion guide bushes corresponds to ISO-n4 (or ISO-h6 for type N 570). The tolerance of the location bore should be selected so that there is no press fit of the guide bush.

We recommend:

  • Mechanical clamping by means of flanges, stop bits, safety rings, etc.
  • Bonding by means of commercially available single-component or two-component systems. The manufacturers’ bonding instructions in terms of the bonding aperture, hardening time, etc. must be adhered to. Experience has shown that a bonding agent that hardens slowly is advantageous.
  • The walls of the bush should not be made too thin. Thin-walled bushes are hard to manufacture and can easily be damaged during installation. Suggested value for wall thickness: Inside diameter d1 · 0.1
  • The required wall thickness is also determined by the type of clamping used.

Separate ball operating zones
 
 

Bonding aperture
 
 

Safety rings
 
 

Flange with stop bit
 
 

Cap                                     Sealing rings, wiper seals
 

Installation with seals

A seal is necessary when there is a lot of dirt present, especially when this takes the form of abrasive substances or if particularly high demands are placed on smooth running, ease of movement and durability.

Sealing options:

  • Sealing rings (see type N 553)
  • Wiper seals (see type N 570)
  • Bellows (see type N 820)
Rotary Stroke Bearings
Mounting the guide shaft
EN

Unlike the guide bush, the guide shaft can be clamped or pressed in.

A radially loaded rotary stroke bearing is subject to elastic deformation on the rolling faces and the guide shaft. The rigidity of the guide shaft is largely determined by the type of clamping used.

With a relatively high load, a long shaft and a need for very accurate guiding over the entire stroke path, at least one of the two holders should be designed with a clamping length of

s >= 1.5 · dw

If there is a clamp on one side only (cantilever beam), the application point of the load should be placed as close as possible to the clamped end.


Beam "on two supports" (loose bearing)
f(a) Deflection at force application point
g(a) Elastic curve

Clamped beam

Pressing in

Make the location bore e.g. ISO-R6 with axis in true alignment. The parallelism deviation of two paired shafts should not exceed the preloading value.

Clamping in the location bore, e.g. ISO-H6

  • Indirectly with a slot and a tension bolt.
  • Directly with a pressure screw. The end of the shaft must be slightly flattened, tapped or turned in to secure it axially.

Clamping in vee-block

  • With a clamp
  • With a tension bolt

Clamping in location bore:Clamping in vee-block:

Adhesive fittings

Poorly aligned location bores can result in tension in the shaft and rotary stroke bearing. This can be prevented by providing the bores with some fitting clearance, e.g. ISO F7-H7. At the final assembly stage, glue the shafts together with the rotary stroke bearing and allow to harden when properly aligned. The manufacturers' gluing instructions in terms of the gluing aperture, hardening time, etc. must be adhered to.

Rotary Stroke Bearings
Installing the ball cage
EN
If ball cages are used in conjunction with open guide bushes, the ball cage and the guide shaft should run together into the bush. Since undersizing (preloading) is employed, this method is only one that can prevent the balls sliding between the bush and shaft.

In the case of rotary stroke bearings with closed guide bushes, the guide shaft must be inserted against the preloading pressure. Lubrication grease is advisable to prevent the balls becoming flattened.

Particularly in the case of ball cages with larger diameters, it must be ensured that the cage is properly centered in the guide bush.
Rotary Stroke Bearings
Limit stops for the ball cage
EN

Despite the fact that the guide moves non-positively subject to preloading, the ball cage can alter its position axially ("cage creeping").

In rotary stroke bearings with an open guide bush, the path of the cage must be limited such that the ball cage cannot move out of the guide beyond a certain amount. This can be ensured by using fixed or sprung stops.

  • Stop bush which is pushed loose over the shaft and stops the cage at the linear reversing points.
  • Clamping bush which can be fixed to any point of the shaft.
  • Safety rings which limit a defined path.
  • Pressure springs.

 

Fixed stops:

Stop bush

Safety rings in the bush

Safety rings on the shaft

Safety rings on the ball cage

 
 
Sprung stops:

Pressure spring on one side

Pressure springs on both sides

Rotary Stroke Bearings
Special constructions
EN

Special designs
Guide shafts

Shafts with the clamping modes illustrated below can be produced on request.

Examples:

• with inside thread
• with shouldered locator shaft with inside or outside thread
• with recesses for safety rings
• with bearing on both sides
• with collar for clamping from above
• with a through-bore for screwing into a vee-block
• guide shafts of special stainless rolling bearing steel 1.4112
• special length guide shafts
• tailstock-sleeves with toolholding fixture

Special designs
Guide bush

In addition to the standard series, guide bushes can be custom-made to suit the customer’s specific dimensions and design requirements.

For example:

• with recesses for clamping with safety rings
• with flange for axial clamping on one side
• with dimensions d1, dB, l1 deviating from the standard dimensions
• made of stainless tool steel 1.4112

Special designs
Ball cages

Special dimensions differing from those listed in the tables are available on request – in small-scale production lots – for all ball cage ranges.

Examples of special designs:

• ball cages with balls in special stainless rolling bearing steel (1.4112)
• ball cages with dimensions differing from those of the standard ranges (dW, l2, k)
• axial ball cages
• ball cages with higher number of balls for particularly high loading

We would be pleased to advise you if you have any questions.


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