WC/WCS series linear shaft

A smooth axis refers to a metal straight axis whose surface has undergone precise processing (usually grinding), has a cylindrical shape, and features high dimensional accuracy, high straightness and low surface roughness. It is a basic component in itself and needs to be used in conjunction with linear bearings (such as linear ball bearings and linear needle roller bearings) or sliding bushings to form a linear motion system.

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Introduction

I. Core Positioning and Definition

Positioning: High-precision, standardized cylindrical linear motion guide rail components. It is a core component of sliding friction or simple rolling friction linear guidance systems.

Key feature: "smooth " is mainly reflected in:

Smooth surface: After fine grinding and polishing, the surface roughness is low (usually below Ra0.8).
Pure shape: It is usually an equal-diameter cylinder without threads, keyways or steps (there may be threaded holes at one or both ends for installation, but the guiding part remains smooth).
High precision: It features strict diameter tolerance, roundness tolerance and extremely high straightness.

II. Core Structure and Types

Classified by material and heat treatment:

Common carbon steel smooth shaft: such as 45# steel, surface high-frequency quenching. Economical, with moderate hardness (HRC50-55) and average wear resistance, it is suitable for light loads.
Bearing steel smooth shaft: such as GCr15 (SUJ2), quenched as a whole. It is the most commonly used, with high hardness (HRC58-62), good wear resistance and excellent core toughness.
Stainless steel smooth shaft: such as SUS440C, quenched. Anti-rust and corrosion-resistant, used in food, medical and clean environments.
Chrome-plated smooth shaft: Hard chromium is plated on a carbon steel or bearing steel substrate. It has a higher surface hardness, is more resistant to corrosion and wear, and has a bright appearance.

Classified by precision grade:

Standard grade: Used for general automated equipment.
Precision grade: Higher straightness, used for precision instruments.
High precision grade: Used for high-end measurement and optical equipment.

Classified by structure:

Solid optical axis: The most common.
Hollow smooth shaft: Reduces weight and can be used for threading wires or passing coolant.

III. Core Features and Advantages

Extremely high cost-effectiveness

Compared with ball/roller linear guides, the combination of a smooth shaft and linear bearings is the lowest-cost linear guidance solution, which is highly suitable for applications that are cost-sensitive and where the load and precision requirements are not extreme.

Flexible design and relatively simple installation

The optical shaft itself has a simple structure and can be easily fixed to the frame through the shaft support (flange type or square type). The layout is flexible and can achieve single-axis, double-axis or even multi-axis support structures.

The system is open and easy to assemble and maintain.

Have basic athletic performance

When used in conjunction with linear bearings, smooth linear motion can be achieved. Although the frictional resistance is higher than that of ball guides, it is much lower than that of ordinary sliding friction.

It can withstand a certain radial load.

Good corrosion resistance and appearance (specifically referring to chrome-plated smooth shafts) :

The hard chromium layer is not only aesthetically pleasing but also rust-proof, making it suitable for equipment with high requirements for appearance.

Standardization and Accessibility

There are standard diameter series (such as φ6, φ8, φ10, φ12, φ16, φ20, φ25...) The length can be customized and the market supply is abundant.

IV. Comparison with the core of ball/roller linear guides (such as MGN/HGH)

Characteristic	Linear Shaft + Bushing System	Ball/Roller Linear Guide (e.g., MGN/HGH)
Guiding Principle	The shaft rotates or remains stationary, while the bushing slides/rolls along it. Typically an open structure.	The carriage block rolls along a precision rail. It is a closed or semi-closed structure.
Friction Type	Sliding friction or low-precision point contact rolling friction.	High-precision rolling friction (balls or rollers).
Rigidity	Low. Acts as a cantilever support, offering very weak resistance to overturning and lateral moments.	Very high. Designed with four-point contact, providing extremely strong resistance to overturning and lateral moments.
Accuracy	Relatively low. Subject to cumulative errors from shaft straightness, bushing clearance, and installation.	Very high. Guaranteed high precision grade (parallelism, straightness) from the factory, offering stable accuracy after installation.
Load Capacity	Acceptable for radial loads, but almost incapable of bearing overturning moments.	High load capacity in all four directions, specifically designed to withstand overturning moments.
Operating Speed	Low to medium. Prone to vibration and heat generation at high speeds.	Suitable for high-speed and high-acceleration motion.
Installation Requirements	Deceptively simple; achieving high precision (e.g., dual-shaft parallelism) is very difficult, demanding high standards for mounting surface machining and adjustment.	Features precision mounting reference surfaces; precision is ensured simply by screw tightening, offering good installation repeatability.
Sealing & Lifespan	Open structure, prone to contamination, requires frequent cleaning and lubrication, resulting in a relatively shorter lifespan.	Integrated multi-layer seals provide dust and water resistance, maintain lubrication well, and offer a long lifespan.
Cost	Very low (for the components themselves).	High
Core Disadvantage	Poor rigidity, low accuracy, and low tolerance for moments.	High cost
Application Philosophy	“Good enough for basic guiding.” Suitable for light-load, low-cost, non-precision applications without significant lateral forces.	“Precise and reliable guiding and load-bearing.” Suitable for applications demanding high load, high precision, high speed, and high rigidity.

V. Typical Application Fields

The optical axis system, with its extreme cost advantage, is still widely used in the following fields:

Lightweight non-precision automation: feeding mechanism, stop-stop mechanism, simple lifting mechanism.
Office and household equipment: The scanning heads of printers, scanners and copiers move.
Light industry packaging equipment: auxiliary guide shafts for labeling machines and packaging machines.
3D printer (low-end FDM model) : X/Y/Z axis guidance.
Sliding parts of doors, Windows and furniture.
Used as a "guide shaft" rather than a "drive shaft" : for example, when paired with a ball screw, the screw is responsible for driving and load-bearing, while the smooth shaft is only responsible for preventing the worktable from rotating (anti-rotation rod).

VI. Selection and Key Points for Use

Recognize the limitations: First and foremost, it is necessary to clarify whether the application has requirements for rigidity, precision and torque. If so, linear guides should be directly considered.
Diameter and length selection: Diameter is the main factor determining rigidity. The greater the length, the larger the required diameter is to prevent sagging due to its own weight. The aspect ratio (L/D) usually has empirical limitations.
Support spacing (key) : The distance (span) between two support points must be as short as possible to minimize bending deformation. For long strokes, a multi-support structure must be adopted.
Paired bearing selection: linear ball bearings (low cost, high speed), linear needle roller bearings (high load capacity, low speed) or oil-free bushings (lowest cost, requires lubrication).
Installation parallelism: When using multiple optical axes, ensuring absolute parallelism is extremely difficult but crucial; otherwise, it will lead to jamming and a sharp increase in wear. Professional tools are required for adjustment.
Lubrication is necessary: Even when using linear ball bearings, regular lubrication is required to reduce wear and prevent rust (except for stainless steel and chrome-plated ones).

The optical axis is the most fundamental, economical, but also most performance-constrained component in the world of linear motion. Its essence is a "precise stick", and its core advantages lie only in low cost and simple structure. In modern precision mechanical design, it is increasingly being replaced by rolling linear guides that have a comprehensive performance advantage. However, in those situations where the load is extremely light, the precision requirements are low, the space is open, and the cost pressure is huge, the optical axis system remains a feasible option that cannot be ignored. Choosing the optical axis means that designers must make a clear and sometimes difficult trade-off between cost and performance.