A lathe center is a tool that has been ground to a point to position a work piece on an axis accurately. The angle of a lathe center is usually 60 degrees, with 75 degrees being used for heavy duty machining.
The primary purpose of a live lathe center is to make sure concentric work is produced, enabling work pieces to be transferred among machining processes without compromising accuracy. A part can be made into a lathe, and sent off for hardening and tempering, then ground in a cylindrical grinder between centers.
A live lathe center, often shortened as a live center, is part of the center family. Unlike a dead lathe center that has not moving part and does not rotate, live centers feature a bearing assembly to allow its tip to rotate with the part so that much less friction is produced between the part and the tip. As a result, faster turning action and higher rotational speeds can be realized.
With the above said, not all live centers are the same as each type is tailored to a suitable application. In this article, we’ll specifically review some of the common types of live centers as well as each of their intended application.
The revolving centers, also known as the rotating center or running center, is a live center often used in the tailstock or non-driven end of a machine. It has a 60-degree angle running in its own bearings which enables superior turning speed without using a separate lubricant, as well as higher clamping pressure.
As a matter of fact, this type of live center is used complementary to CNC lathes almost exclusively. It is often used for standard machining operations as well. Some revolving centers also possess interchangeable shafts which is especially valuable for application that requires a design without using the 60-degree tip.
A pipe center is also referred to as the bull nose center. Rather than the standard sharp point, this type of live center has a conical nose with large diameter. This make the lathe center the perfect choice the bore of a pipe and other work pieces with relatively larger diameters.
While a pipe center ensures that the work piece stays focused, its main benefit is that it firmly supports the work piece and can be used for parts whose larger inner diameter prohibits a standard pointed center from being used. If excessive force is applied at the chuck end, thin-layered material such as pipes can collapse easily.
There are essentially two types of cup centers: One for woodworking which makes up the majority of applications, and another for metalworking. The woodworking type of cup center has a central point that resembles a standard live center with a ring surrounding it. The ring functions as a protection of the softer material around the center point which prevents the wood from splitting due to pressure applied from the central point.
Another type of cup center is mainly used for metalworking, and can be further divided into a variety of subtypes based on the material condition. This type of cup live center has a tapered hole instead of a conical point. Unlike its counterpart, a metal working type live center does not support the part by using a center hole, but by making contact with the outside diameter of the part instead.
The design of this type of live center is derived from the principle of machine tool spindles. It has three angular contact bearings secured to the rotation point with a needle-roller and a locknut bearing behind the point.
The bearings allow rapid rotation while retaining the needed rigidity of the live center. This type of live center is representable by its sturdiness, versatility, rigid head for enhanced stability and support, and longer and thinner head for increase tolerance. It can be used for most operations.
This type of live center is a high quality and highly precise tool that is specifically designed to accommodate high speed turning applications. Its spindle speed can go up as high as 12,000 rpm. To minimize the heat generation and turning resistance from the high speed, precision live center is lubricated with lightweight spindle oil rather than grease. This type of live center utilizes an extended point that comes with both carbide and steel tips, which is said to provide optimal balance between tool tolerance and rigidity.
Heavy duty center is specifically designed to accommodate heavier work pieces. To achieve so, the angular contact bearings have to be made larger than the normal ones, and secured in a stable assembly. A heavy duty center also has a thick, rigid point that extends into the shank where support is offered by a wide, needle-roller bearing. It is said that this type of center can accommodate work pieces as heavy as 12,000 pounds with these features.
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