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Linear shafts: shaft ends and mounting options for linear shafts
The fastening mechanisms for linear shafts or guide shafts in mechanical systems require careful planning. Different shaft ends permit different mounting options. This article provides an overview of available shaft ends and answers the question of which shaft holders or shaft support options are available and where they are appropriate. As part of this, we also take a detailed look at the fixed and floating bearing types for shafts.
What is a linear support?
The fastening mechanisms for linear shafts or guide shafts act as precision locating mechanisms in mechanical systems. Common mounting options for linear shafts include end washers, clamping fasteners or adjusting rings. Many of the mounting options can also be used for standing torque shafts, where they prevent axial movement while absorbing and dissipating torque exerted on the shaft into the machine housing.
Fixed and floating bearings for shafts
Typically, two bearings are required to support shafts and axis. In order to allow expansion, a fixed-floating bearing is recommended for shafts in most cases. The floating bearing acts as the radial support and axial guide for the shaft while allowing movement in axial direction. In contrast to the floating bearing, a fixed bearing fixes the shaft in axial direction. The fixed bearing becomes the reference point in the combination of floating bearing and fixed bearing.
Why is the combination of fixed bearing floating bearings appropriate for a shaft? If the shaft is for example installed with two roller bearings, there is a defined play inherent to the design. This play changes as heat builds up during operation; the shaft expands. The floating bearing now compensates for these distance differences, as it allows axial movements. This leads to a longer service life of the installed rolling bearings and the system as a whole.
Various connection options for linear shafts
Interlocking fit is a connection created when the components to be connected are mated together based on their shape. The shape prevents movement. For example, shaft grooves are used for shafts. In combination with a retaining ring, they precisely position the shaft axially. This type of interlock is for example appropriate to positively prevent linear movements and to prevent pull-out. However, precision adjustments are difficult. By contrast, a friction lock generates a contact force, usually with screws or clamps, that connects the respective components to one another. For shafts, this is for example accomplished with clamping screws or clamping sleeves, which provide a very stable connection after tightening. A prior precision adjustment remains possible. When used accordingly, a friction-lock can also prevent twisting in addition to fixing the axial position.
Friction locks are usually implemented as a circumferential clamp or as a clamp with grub screw. A circumferential clamp or clamp connection creates a compression over the circumference of the shaft, which secures the shaft against twisting and axial movement. It is also appropriate for higher torques. There are different concepts for implementing a circumferential clamp. This includes, for example, conical clamping elements or clamp connections with half shells. On some of these, such as the clamp connection with half shells, their asymmetric structure may cause an uneven surface compression and an out-of-balance condition.
If the shaft is clamped with a set screw, the shaft is held in position by the set screw. Tightening the set screw damages the shaft surface, which can subsequently interfere with disassembly due to the small gap. This can for example be prevented by point drilling the shaft before assembly. Clamp with set screws should only be used in applications with low torques, low axial loads, and low speeds. It allows for easy and fast assembly and disassembly in difficult-to-reach installation spaces. For a secure connection without damaging the components, the required tightening torque of the set screw must be observed.
Shaft ends for supporting linear shafts
The shaft end is not just the end of a shaft. The design of the shaft ends significantly influences the installation options of the shaft, the precision during assembly and alignment and the stability of the connection between the shaft and bearings or shaft coupling or machine housing. A shaft end can also act as a interface for further components, and mechanical energy is often supplied or dissipated over the shaft end. There are various standards for the different versions of shaft ends. Cylindrical shaft ends are for example standardized iaw. DIN 748 - Cylindrical shaft ends, dimensions, nominal torques.
The following table provides a partial overview of various shaft end configurations and their mounting options:
| Geometric shape of the shaft (example) | Detail image | Potential uses | Examples and properties of joining The two-sided mounting is preferential | Bearing seal |
|---|---|---|---|---|
| Stepped by 1 increment |  |
 |
- stepped shaft enables an extremely precise mounting due to fit - stepped as a stop serves as a restriction in an axial direction - secured in both axial directions possible via a shaft holder screwed to the component or through gluing - less used for linear shafts, otherwise it can be used as a floating bearing |
- fixed bearing: press-fit - press fit - floating bearing: floating bearing seal - clearance fit - bonding possible as fixation |
| Stepped by 2 increments |  |
 |
- stepped shaft enables an extremely precise mounting due to fit - stepped as a stop serves as a restriction in an axial direction - secured in both axial directions possible via a shaft holder screwed to the component or through gluing - less used for linear shafts, otherwise it can be used as a floating bearing |
- fixed bearing: press-fit - press fit - floating bearing: floating bearing seal - clearance fit - bonding possible as fixation |
| Stepped with threaded pin in fitting diameter |  |
 |
- highly accurate mounting is possible with a threaded pin and fitting hole at the bearing point - stable under heavy loads, horizontally and for long lengths |
Fixed bearing |
| Stepped with threaded hole, front |  |
 |
- highly accurate mounting is possible thanks to a stepped shaft with fitting and threaded holes - stable under heavy loads, horizontally and for long lengths - the shaft diameter can be freely adjusted according to the drill holes |
Fixed bearing |
| Stepped with ring groove (stationary axle) |  |
 |
- not suitable as fixed bearing for linear shafts as the circlips are limited in terms of axial load bearing capacity - no anti-twist protection | Floating bearing |
| Clamping surface, one-sided/D-shape |  |
 |
- anti-twist protection - length compensation is possible in case of temperature fluctuations |
Floating bearing |
| Internal thread, front, double |  |
 |
- counterbore/fitting hole allows for highly accurate mounting by fitting with shaft - stop and locking is possible in both axial directions via 2 screw connections with component - anti-twist protection - also suitable for mounting a torsion-proof end disc |
Fixed bearing |
| Internal hexagon, front |  |
 |
- as an alternative to the key area in critical installation conditions - front internal hexagon for easier shaft mounting - serves as a drive for shafts with threads at the other shaft end, among other things |
- |
| Tapered |  |
 |
- primarily as a mounting aid (insertion aid) - simplifies mounting of sealing rings or linear bearings without damaging them - unsuitable for the use with frequent installation with linear bushings. (It may damage the linear bushings.) |
- |
| Fitted hole with stepped threaded hole, front |  |
 |
- a fitting screw as a guide/centering in combination with the fitting hole of the shaft and threaded holes enables extremely precise mounting. - stable under heavy loads, horizontally and for long lengths |
Fixed bearing |
| Ring groove for shaft retaining ring |  |
 |
- unsuitable as a fixed bearing for linear shafts as the circlip in axial load-bearing capacity - no anti-twist protection - can also be used as a fixed bearing in combination with a shaft holder bolted to the support structure. |
Floating bearing |
| Threaded hole, front and spanner flats |  |
 |
- exact mounting is possible due to fit - locking in axial directions via front screw connection - key areas for simple mounting in confined spaces - with a conical through hole, the shaft; it can be centered in the cone and pressed - if in doubt, secure by gluing |
Fixed bearing |
| Transverse spring groove (keyway) |  |
 |
- exact mounting is possible due to fit - locking in axial directions via keyway - anti-twist proof due to the key |
Fixed bearing |
| Wrench flats/clamping surface - flattened on two sides at the end with locking groove and transverse internal thread for lateral tension |  |
 |
- for tensioning or parallel alignment of shafts | Floating bearing |
| Tapped hole crosswise for shaft support profiles |  |
 |
- linear shaft bolted to shaft support profile | Fixed bearing |
| Straight solid shaft |  |
 |
- simple shape - mounting in conjunction with shaft holders |
Fixed bearing |
| Solid shaft with external thread in shaft diameter |  |
 |
- easy installation - inaccuracies possible due to thread tolerances - if in doubt, secure by gluing |
Floating bearing/fixed bearing |
| Solid shaft with internal thread/threaded hole, front |  |
 |
- easy to mount with screws through due to through holes - low accuracy of the mounting position - horizontal fastening in low load applications |
Fixed bearing |
| Groove for set screw |  |
 |
- grub screw clamping/clamping screw clamping - without risking shaft surface damage |
Fixed bearing |
| Stepped by 2 increments and threaded pin |  |
 |
- highly accurate mounting is possible due to a stepped shaft with a fit and threaded pin - the stepping enables limiting the axial direction - shaft diameter can be freely varied when multiple shafts are used in a base plate with the same bore diameter - if in doubt, secure by gluing |
Fixed bearing |
| Front threaded hole and cross hole |  |
 |
- secured against axial tension - cross hole as a mounting aid in difficult-to-reach areas - if in doubt, secure by gluing |
Floating bearing |
note that the illustration is simplified. Different ends on the left and right are possible.
Shaft supports for securing linear shafts
Shaft supports, also known as pillow blocks, connect rigid shafts, axis and other components together in an overall system. They also act as horizontal or vertical bearings for axes and linear shafts. The compressive and tensile loads are transferred from the axis through the shaft supports into the machine housing or the load-bearing structure of the application. Identical fastening options apply for hollow shafts. The variant with support rail is also an option for open bearings with a segment cutout suited for supported linear shafts. This support rail prevents the shaft from sagging by supporting the shaft along its entire length.
Different shaft supports can be used depending on the application requirements. MISUMI offers different shapes of shaft supports:
- T-shape: This shaft support is upright. It consists of a base with a vertical bore for the shaft and allows for stable fastening.
- L-shape: Right-angled shape that allows for lateral attachment of the shaft.
- Block shape: Cuboid, robust construction that provides high stability and load capacity.
- Round: Cylindrical shape for uniform shaft support.
- Round flange: Round support with flange for stable mounting and precise alignment. Facilitates attachment to various surfaces.
Below are some shaft supports presented in detail:
Shaft flanges
Flanged brackets provide high stability because the flange is attached to the shaft. Shaft flanges are often installed in applications with vertical stroke. MISUMI has options to configure this package with slit clamp and clamping screw. A low-profile, round shaft flange can be used if installation space is limited.
MISUMI offers a rear mounting option as a special shape for shaft flanges. For this purpose, the rear of the shaft flange has a counterbore for a cylinder head screw used for securing the shaft. This installation method requires a linear shaft with internal thread on the front face. This type of fastening eliminates the need for further clamping.
Set collars and clamping rings as shaft supports
Set collars, also called clamping rings, are suited for locking shafts and can act as a stop and also as a positioning device. They secure the shaft in a predetermined position. The set collar can be mounted anywhere on the shaft, eliminating the need for a shaft shoulder. The flexible mounting also allows set collars to be used as shaft supports at the shaft end. MISUMI offers a variety of designs:
- Set collar with grub screw
- Clamping ring with slit
- Set collar with slit and clamping lever
- Set collar with keyway
Two-piece set collars are split in the center. Using two screws, the shells are tightened against each other to generate the clamping force on the shaft. The two-piece design allows for easy assembly in confined spaces. During maintenance, the set collar can be easily removed without having to remove the shaft.
High clamping forces can occur when clamping with set collars with slits. The position can be freely selected since fastening does not require a flat surface on the shaft. The slotted and the two-piece set collar both distribute the clamping force over the entire contact surface, resulting in a high clamping effect without damaging the shaft surface.
Shaft support for limited installation space
Shaft supports are not only used in large machines. Shafts and shaft supports can also be used in precision mechanics, e.g. for optical devices. For those cases with limited space, MISUMI offers particularly small and low-profile shaft blocks. On these shaft blocks, the mounting holes are located on the side, allowing them to be installed in tight spaces. Depending on the shaft diameter, the resulting shaft height is therefore approx. 5 mm.
