Benefits of precise linear movements: everything about linear shafts

Linear shafts are high-precision and robust machine elements and, in conjunction with linear bearings, enable controlled, linear guided movement. The full or cylindrical components, which are available with a cylindrical or hollow shaft and are often offset on one or both sides, generally serve as guides for linear ball bushings or linear plain bearings located on the shaft.

Linear shafts offer a high degree of precision in movement, are highly configurable parts and are usually made of steel or stainless steel. Through different designs of the shaft ends and optional surfaces and if necessary heat treatment, linear shafts can be adapted to the specific requirements of the respective application in mechanical engineering.

Linear shafts, as one of the possibilities for implementing a linear guide, offer high rigidity with relatively low maintenance requirements and a long service life.

Where are linear shafts used in technology?

Linear shafts are used for guided axial movement and can be used for both horizontal and vertical linear movements. They are utilized in almost all industries in the field of plant and mechanical engineering. For example, they are utilized in 3D-printers, dosing systems, measuring devices, positioning and alignment devices, bending devices and sorting systems. Linear shafts are known for their precision and lifetime. They are therefore often utilized in applications with high demands on these properties, for example in lifting movements.

Linear shafts are available in various sizes and lengths for almost any application and can be easily configured and ordered online.

A few facts about linear shafts

• Linear shafts are usually made of steel or stainless steel
• Linear shafts are very robust and enable highly efficient, precise movement
• A variety of possible shaft end designs are available
• Depending on the application, linear shafts can be manufactured without additional heat treatment or induction hardened
• The surface layer of the raw material is hardened before grinding. This means that treated areas, such as key surfaces have a different surface hardness
• The surface may be untreated, hard chrome plated, low temperature black chrome plated (LTBC) and chemically nickel-plated
• Coatings and platings are applied to the raw material after hardening and grinding, but prior to further processing. Machined areas, such as flat surfaces and threads, may therefore be uncoated
• MISUMI linear shafts are offered in ISO tolerances f8, g6 and h5

How does a linear shaft work?

Linear shafts can usually be integrated with relatively little technical effort and enable very precise linear guide. For this purpose, the linear shaft is usually supported by two or more shaft holders or ball bearings supported in the machine frame.

In principle, a linear shaft can also be subjected to torsion, but this is usually not desired since it is used as guide component. As a rule, the linear shaft is therefore fixed and does not transfer any rotary motion, but is mainly subjected to bending stress. If two parallel linear shafts are used, as in this example, torsional stress is nearly eliminated.

What is the difference to a linear rail?

Linear shafts are precision-ground, round shafts that, in combination with linear ball bushings or plain bearing bushings, enable linear guide.

On the other hand, linear rails, also known as profile rails, are rails that work in conjunction with supports (freewheel bodies, carriages) according to the rolling or sliding principle. These components also enable linear movements.

Linear shafts enable precise results in 3D-printing

3D-printers are often utilized in the industry to produce prototypes and individual parts. The 3D-templates are constructed and transmitted to the device with the help of software. The 3D-printing is then done by applying the material layer by layer. The high precision of the linear shafts and linear drives enable producing complex and precise 3D-print products.

As a reliable and precise technology, linear shafts and linear drives form the basis for interaction with all other components of the 3D-printer to transform efficiently and precisely materials such as plastics, metals, sand, wax, resins and ceramics into three-dimensional objects.

How do you distinguish between linear shafts, rods and rotary shafts?

When considering whether to select a linear shaft, rod and rotary shaft for your applications, remember that each has its own advantages- and disadvantages.

Linear shafts are precision-machined shafts and are used as leading axles in machines. They are manufactured with high precision and are often firmly connected to the machine frame via shaft holders. They form the guide for one or more linear bearings, which can be moved axially while guided on the linear shaft. Linear shafts are mainly subjected to bending stress.

What is a rod?

Rods are usually understood as raw materials. As opposed to a shaft, they usually have a higher tolerance when delivered. An exception to this are precision rods, which are also available in higher precision. Bars and rods are some of the simplest parts in a machine and can be a good choice for applications with lower surface finish and tolerance requirements. Rods are generally not used for direct force transmission (linear movement/rotation), but may be suitable for this purpose depending on the material.

Rods and bars are available in round, hexagonal or square shapes and can be used as spacers or to join multiple components. Since rods and bars are only machined or treated to a limited extent, they may need to be additionally machined and adapted to your intended application.

What is a rotary shaft and what is the axis of rotation?

As opposed to linear shafts, the main application of rotary shafts is the transmission of rotary movements and moments. They are used, for example, as a rotary shaft between the motor and the gear box. Rotary shafts are primarily subjected to torsions and must meet high demands on torsional rigidity, straightness and concentricity.

The axis of rotation, shown in yellow in the picture, is the axis around which a component such as a rotary shaft rotates. If the axis of rotation does not exactly correspond to the axis of inertia, an imbalance occurs. Imbalances may cause rotating parts and mechanical structures to vibrate, which may not only lead to increased wear but even to the failure of a component.

How are linear shafts configured?

In order to use a linear shaft permanently and reliably, you must determine in advance the requirements of the planned application and the resulting required properties of the linear shaft.

To configure a linear shaft that is adapted to your desired application, you can use our linear shaft configuration.

1. Select the appropriate basic shape (e.g. solid shaft, hollow shaft, offset on one side or both sides)
2. Select the appropriate end shape for both shaft ends (e.g. straight, inside or external thread, conical). You can find more information in the blog Wave Guide Shapes.
3. Select the appropriate basic properties (e.g. material, hardness, coating, tolerance). Read more about tolerance classes, geometric tolerances and surface treatment.
4. Select the specific dimensions (length, diameter).
5. You can then order the configured linear shaft directly or download a CAD model (2D-model/3D-model) of the configured shaft from our CAD library.

You can then import the downloaded model directly into your CAD drawing.

Shaft holder

Shaft holders are a valuable connecting element for rigid shafts (axles) or for linear shafts. The holders for shafts and axles, which are available in many designs and materials, enable easy integration and can usually be customized to your needs. Shaft holders “clamp” the shaft to hold it securely. For floating bearings and the bearing of rotating shafts, a bearing with a housing or a pillow block is usually used.

If you have to choose one of the shaft types mentioned, you should consider the specific requirements of your application and select the optimal shaft holders or pillow blocks.

The matching parallel keys

A parallel key is a solid, elongated metal part that is inserted into a correspondingly milled keyway in the shaft and protrudes from it. The corresponding hub is provided with a continuous and cleared groove that matches the parallel key and is pushed axially over the parallel key. To ensure axial fixation on the shaft shoulder, retaining rings or lock nuts are usually used. The shaft hub connection implemented in this way is positive-locking and, when designed accordingly, reliably transfers torque from, for example, a shaft to a gear wheel or vice versa.

MISUMI parallel keys are manufactured similarly to the standard DIN6885 defined shapes and specifications and key steel similar to the specifications of the standard DIN6880.

Quality control for linear shafts - How you can achieve precise results

At MISUMI, customers can request make-to-order (MTO)-components according to their specifications. Various geometries, final shapes and materials as well as surface finishes (untreated, burnished and nickel-plated) are available. The shaft diameter of the components may vary between 2 and 50 mm.

MISUMI uses the particularly precise tolerances h5/g6 for many components. For further information please use our tolerance tables according to JIS B0401-1, -2 (1998). They are consistent with all standard tolerance specifications and guidelines.

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