The guide rails of ordinary lathes in the early days were hard rails. Hard rails are obtained after heat treatment, grinding and scraping. The production cycle is long and the processing technology is difficult. Now, in order to reduce the workload of scraping, plastic pasting is generally used. Hard rails have large friction, large inertia and high strength. They are now generally used on economical and heavy-load CNC machine tools. Linear rails are now used on CNC milling machines and multi-axis machining centers. The friction is small, the machine tools are sensitive and the inertia is small. Generally, they are fixed to the bed through multiple sets of pressure plates. They are easy to install and adjust, but the strength is not as good as hard rails, and heavy-load processing may bend. Slide rails are round rails. The performance is similar to that of linear rails. They are generally used in light-load brackets such as inkjet printers and plasma cutting machines~

The machining center is divided into hard rails and linear rails. There are two types of linear rails: ball rails and roller rails. The linear rails have fast movement speed, high precision and good stability. After pre-tightening, the linear rail can achieve zero clearance between rails and full load capacity in all directions.

Hard rails are also called wide rails or square rails. Hard rails can only move if there is a gap on the moving surface, and the friction coefficient is large, which is easy to cause adhesion, resulting in processing errors. In the past, it was mostly used in heavy loads. After the guide rails are worn, the linear rails are easy to replace, and the hard rails are very troublesome because they need to adjust the clearance. 

Now most machine tool manufacturers at home and abroad use linear rails in large quantities. Now the width of the linear rails can be made larger. The load-bearing capacity has been greatly improved. A large number of gantry machining centers use linear rails in large quantities. Three or four rails are mostly used. Hard rails and linear rails are both structural methods for linear motion on machine tools, such as the movement of workbenches.

Linear rails usually refer to rolling guides, and this type of component is often called "linear guides". The linear guide itself is divided into two parts: the slide rail and the slider. There are internally circulating balls or rollers in the slider, and the length of the slide rail can be customized. It is a modular component, a standardized series of individual products produced by a special manufacturer, which can be installed on the machine tool and can be disassembled and replaced after wear. Linear rails are rolling friction, fast speed, low resistance, and easy lubrication. Now more and more machine tool industry uses linear rails, but high-end imported machines still use hard rails more and more, and domestic regular brand machining centers also use hard rails more and more. The guide rails and the bed of the hard rail are one-piece castings, and then the guide rails are processed on that basis, and then processed into guide rails after quenching and grinding. Now there are also bed and guide rails that are not necessarily integrated, such as steel-inlaid guide rails, which are nailed to the bed after processing. Hard rails are guide rails that are sliding friction, have good rigidity and strong load-bearing capacity.