Understanding the Difference Between Hard Rail and Linear Rail in CNC Machining Parts

 

 

 

Hard rail refers to the casting that integrates the guide rail and the base, and the guide rail is machined according to the casting when the CNC machined parts. That is, the shape of the guide rail is cast on the bed, and then machined by quenching and grinding. The bed and the guide rail are not necessarily integrated. For example, nailing steel rails to the bed after CNC machining. Linear guides for machine tools that use hard rails usually refer to rolling guides, which are the kind used in linear modules, which are now often used in the machine tool industry. We usually refer to these types of components as "linear guides".

 

In the field of CNC machining, the choice between hard rail and linear rail systems plays a crucial role in determining the performance and functionality of the machine. Both hard rail and linear rail systems have their own set of advantages and disadvantages, and understanding the differences between them is essential for making an informed decision. This article aims to provide a comprehensive overview of the disparities between hard rail and linear rail in CNC machining parts, enabling readers to make an educated choice based on their specific requirements.

 

 

 

Introduction

 

CNC machining is a manufacturing process that utilizes computer numerical control (CNC) systems to control machine tools. It enables precise and efficient production of complex parts and components. In CNC machines, the movement of the cutting tools is facilitated by rail systems, which guide the motion along a specific axis. Two common types of rail systems used in CNC machining are hard rail and linear rail.

 

 

 

Understanding Hard Rail Systems

 

Hard rail, also known as boxway or box guide, is a traditional rail system widely used in older CNC machines. It features a robust design with hardened and ground surfaces that provide excellent rigidity and support. The hard rail system consists of metal sliding surfaces and lubrication channels that ensure smooth movement. It is often preferred for heavy-duty machining operations that require high load capacities and stability.

 

 

 

Exploring Linear Rail Systems

 

 

Linear rail, also called linear guide or linear motion system, is a modern rail system that has gained popularity in recent years. It utilizes a series of rolling elements, such as balls or rollers, to enable precise linear motion. The linear rail system offers low friction and high-speed capabilities, making it suitable for applications that demand rapid movements and accurate positioning. It is commonly found in modern CNC machines and offers several advantages over hard rail systems.

 

 

 

Rail machining center machine

 

 

Its full name is linear guide machining center machine tool, generally refers to rolling guide. There are two common structures: rails and roller rails. The difference is that the guide rail is a point contact type, and the roller guide rail is a line contact type. Their principle is the same, they are all driven by rolling on the guide rail.

 

The CNC bed is composed of hard rails and linear rails. The hard rail has good rigidity and is suitable for manufacturing steel CNC machined parts. Line rails are specially used for aluminum CNC machining parts because of their fast moving speed, but their rigidity is not as good as that of hard rails. Therefore, the feed (XY direction), bottom feed (z direction) and feed rate of aluminum parts processed by hard rail machine tools will have advantages over rail machine tools.

 

According to the size of the spindle taper hole, CNC machining centers are divided into BT 30, BT 40, and BT 50. BT 30 is the smallest and BT 50 is the largest. The taper hole not only determines the size of the spindle and the force stiffness of the spindle, but also determines the outer diameter of the tool holder. The larger the spindle taper hole, the larger the handle, the better the rigidity, and the larger the parameter.

 

In addition to the cooling system, oil cooling has the best effect, followed by water cooling, and air cooling is only used when necessary. It also affects processing parameters.

 

 

The stricter the customer's requirements on appearance, the smaller the cutting amount, and the slower the feed speed.

 

 

Advantages:

 

1. The linear guide is supported by rolling parts, the rolling and sliding performance is better than the friction and sliding performance of the hard rail, and there is no creeping phenomenon;

 

2. The friction coefficient is small and the movement speed is fast;

 

3. The friction coefficient is small, and the wear is small;

 

4. Under normal circumstances, the linear guide is composed of better materials and more precise equipment, so its accuracy is also higher;

 

5. Convenient for later maintenance. After the guide rail is worn out, it is convenient to replace the line track, because the gap needs to be adjusted, and the hard track is troublesome.

 

 

 

Disadvantages: Due to the small contact surface, the rigidity is lower than that of the hard rail.

 

 

Advantages, disadvantages and applications of hard rails in CNC machining parts: hard rails have large sliding contact surfaces, good rigidity, strong shock resistance, and strong load-bearing capacity, suitable for heavy-duty cutting. The hard rail is dry friction. Due to the large contact surface, the frictional resistance is also large, and the moving speed cannot be too fast. At the same time, crawling is easy to occur, and the gap on the moving surface can cause CNC machining errors. Maintaining machine tool tracks is a top priority. Once the track lubrication is insufficient, it will cause the track to burn or wear, which is very important to the accuracy of the CNC machining machine tool. The application of hard rail is suitable for heavy cutting, large molds, high hardness workpieces, and CNC machining parts with general accuracy requirements.

 

 

 

 

 

 

 

 

Hard track machining center

 

 

The integral casting of a stock index guide rail and the bed, the material quantity is generally not less than HT250, and the Brinell hardness of the body is between hb180-hb240. The hardness of the guide rail after high frequency or super audio frequency quenching is generally above 50%, and it has good wear resistance (steel inlaid guide rail is also a kind of hard guide rail). The hard rails used in CNC machining centers are generally rectangular, commonly known as rectangular rails.

 

Advantages: The sliding friction surface of the hard rail is large, the machine has strong rigidity and good stability.

 

Disadvantages: Due to the large contact surface, high friction resistance, fast wear, and limited movement speed, defects such as crawling are prone to occur. Therefore, most of the machining factories use the jamming process to reduce the wear and creep defects of the hard rail.

 

 

In CNC machining parts, the advantages and disadvantages of linear rails and their applications. Nowadays, many CNC machining machine tools run very fast, especially idling speed. This is largely due to the linear guide. Linear guide rails can be pre-tensioned to achieve a high-precision zero gap between the guide rails.

 

In terms of service life, linear guides are much higher than hard rails. The cutting force of the linear guide is smaller than that of the hard guide. Only used for hard tracks. In fact, the linear guides of many CNC machining machine tools have greatly improved their load-bearing capacity. The application of linear guide is suitable for high-speed machines, high-speed cutting, suitable for CNC machining parts and small precision molds.

 

 

Today, more precise CNC machining centers use linear guides.

 

 

 

Comparison of Hard Rail and Linear Rail

 

 

1. Precision and Accuracy

 

In terms of precision and accuracy, linear rail systems outperform hard rail systems. The rolling elements in linear rail minimize friction, reducing the chances of stick-slip motion and enhancing positioning accuracy. On the other hand, hard rail systems may experience more friction, leading to slight inaccuracies over time.

 

 

2. Load Capacity

 

Hard rail systems excel in load-carrying capacity due to their robust construction. They can withstand heavy loads and provide stability during machining operations involving significant cutting forces. Linear rail systems have a relatively lower load capacity but are suitable for applications with moderate loads.

 

 

3. Maintenance and Durability

 

Hard rail systems are known for their durability and resistance to wear and tear. However, they require regular maintenance, including lubrication, to ensure optimal performance. In contrast, linear rail systems are relatively low maintenance, as their rolling elements experience less friction and wear.

 

 

4. Speed and Performance

 

When it comes to speed and performance, linear rail systems have the advantage. The reduced friction in linear rail enables higher acceleration and deceleration rates, resulting in faster machining times. Hard rail systems may have limitations in terms of speed, making them more suitable for applications that prioritize precision over speed.

 

 

5. Cost and Affordability

 

Hard rail systems are often more affordable initially, making them a cost-effective choice for budget-conscious buyers. However, they may incur higher maintenance costs over time. Linear rail systems tend to have a higher upfront cost but offer better long-term cost efficiency due to their lower maintenance requirements and improved performance.

 

 

6. Application Considerations

 

The choice between hard rail and linear rail depends on the specific application requirements. Hard rail systems are well-suited for heavy-duty machining, such as milling large components, while linear rail systems are ideal for applications that demand high-speed and precise movements, such as engraving or small parts production.

 

 

 

Conclusion

 

In summary, the difference between hard rail and linear rail systems in CNC machining parts lies in their construction, performance, and application suitability. Hard rail systems offer robustness and high load capacity, while linear rail systems provide superior precision, speed, and low friction operation. Understanding the disparities between these two rail systems is crucial for selecting the right option based on the specific needs of a machining application.

 

 

 

 

FAQs

 

 

Q1. Which rail system is better for heavy cutting operations?

 

For heavy cutting operations, hard rail systems are typically preferred due to their robustness and high load capacity.

 

 

Q2. Can linear rail systems be retrofitted into older CNC machines?

 

Yes, linear rail systems can often be retrofitted into older CNC machines to enhance their performance and precision.

 

 

Q3. Are linear rail systems more expensive than hard rail systems?

 

Linear rail systems tend to have a higher upfront cost, but their long-term cost efficiency, lower maintenance requirements, and improved performance make them a worthwhile investment.

 

 

Q4. Do linear rail systems require lubrication?

 

Linear rail systems require minimal lubrication compared to hard rail systems due to their reduced friction design.

 

 

Q5. What are some common applications of linear rail systems in CNC machining?

 

Linear rail systems are commonly used in applications such as engraving, small parts production, and operations that require high-speed and precise movements.