What Is a Guide Bushing?
A guide bushing is a fixture used in automatic lathes with spindle movement for precision component machining. Its purpose is to precisely hold the workpiece during processing.
Automatic lathes are machines that rotate the spindle gripping the material with a chuck while performing cutting operations with blades. There are two types of automatic lathes: those with a spindle that moves in the Z-direction while bringing the workpiece into contact with the blade for cutting (spindle-moving type) and those with a fixed spindle while moving the blade for cutting (spindle-fixed type).
In both types of automatic lathes, when the distance from the chuck, holding the material, to the blade becomes long, deflection and vibration increase, making precise machining difficult. Therefore, in spindle-moving automatic lathes, the guide bushing is used near the cutting point to hold the material, enabling higher precision machining. This fixture is referred to as the guide bushing.
Uses of Guide Bushing
The guide bushing is used in spindle-moving automatic lathes to accurately hold the material, enhancing the precision of cutting operations. However, while it is an essential fixture for spindle-moving automatic lathes, there are cases where it is not used.
Spindle-moving automatic lathes are suitable for machining thin and long precision parts. Originating in Switzerland and known as Swiss-type automatic lathes, these machines were developed for machining precision parts for watches. Guide bushings prove useful when dealing with product shapes that result in long distances between the chuck and the part where the blade makes contact, or when the material itself is thin and prone to deflection. The application of guide bushings extends beyond watch components to various industries, including medical devices, aerospace parts, and automotive components.
Principle of Guide Bushing
The guide bushing is fundamentally cylindrical and is attached just before machining in a Swiss-type automatic lathe. In addition to cylindrical guide bushings, there are square and hexagonal variations. The mainstream materials are steel with attached carbide, although some feature ceramics or cermet.
Attachment methods include a taper at the end of the guide bushing for press-fitting or a threaded part for screwing. Some guide bushings have a flange with screw holes, allowing them to be securely attached to the main body using screws.
Guide bushings play a role in supporting materials in extremely narrow gaps during installation, allowing the material to rotate while minimizing deflection and vibration. In addition, they are designed to enable the material to move in and out in the Z-axis direction along with the spindle’s Z-axis movement. Consequently, machines that synchronize the rotation of the guide bushing with the spindle’s rotation have become prevalent.
Some automatic lathes allow machining without using guide bushings, providing guide bushing detachable models. While guide bushing mechanisms inevitably result in the waste of material at the end of the spindle collet chuck to the guide bushing, guide bushing-less mechanisms allow more economical utilization of the material until the end.
How to Choose Guide Bushing
The shape, size, and attachment method of usable guide bushings vary by automatic lathe manufacturer. When selecting guide bushings, the first step is to choose from products compatible with the automatic lathe used in-house.
Choosing a guide bushing with a smaller difference between the material’s outer diameter and the guide bushing’s inner diameter makes it easier to prevent deflection and vibration, enhancing performance.
Moreover, considering the surface condition of the material, it is crucial to select the material and surface treatment of the guide bushing appropriately. For instance, when machining hard materials like stainless steel or titanium alloys, opting for a high-wear-resistant guide bushing, such as one with attached carbide, is advisable.