Turning Tools

Turning is the process of using lathes to remove material from the outer diameter of a rotating workpiece. Single-point tools shear metal from the workpiece in (ideally) short, distinct, easily recyclable chips.

Source: Machining 101: What is Turning?

Early turning tools were solid, rectangular pieces of high-speed steel with rake and clearance angles on one end. When the tool dulled, machinists would sharpen it on a pedestal grinder for reuse. High-speed steel tools are still common on older turning machines, but carbide has become more popular, especially in brazed single-point form. Carbide sports better wear resistance and hardness, leading to better productivity and tool life, but it is more expensive and requires expertise to resharpen.

Source: Machining 101: What is Turning?

Turning is a combination of linear (tool) and rotational (workpiece) movement. Thus, cutting speed is defined as the rotational distance (recorded as sfm — surface feet per minute — or smm — square meters per minute — traveled in one minute by a point on the part surface). Feed rate (recorded in inches or millimeters per revolution) is the linear distance that the tool travels along or across a workpiece surface. Feed is also sometimes expressed as the linear distance the tool travels in a single minute (in./min or mm/min).

Feed rate requirements vary depending on the operation’s purpose. In roughing, for example, high feeds are generally better for maximizing metal removal rates, but require high part rigidity and machine power. Finish turning, meanwhile, might slow down the feed rate to produce the surface finish specified on the part blueprint.

Source: Machining 101: What is Turning?

Boring is primarily used for finishing large, cored holes in castings or pierced holes in forgings. Most tools are similar to those in traditional, external turning, but cutting angles are particularly critical due to chip flow concerns.

Source: Machining 101: What is Turning?

The spindle on a turning center is either belt-driven or direct-drive. Generally, belt-driven spindles represent older technology. They speed up and slow down at a lower rate than direct-drive spindles, which means cycle times can be longer. If you’re turning small-diameter parts, the time it takes to ramp the spindle from 0 to 6,000 rpm is significant. In fact, it might take twice as long to reach this speed than with a direct-drive spindle.

A small degree of positional inaccuracy may occur with belt-driven spindles, because the belt between the drive and the positional encoders creates a lag. With integral direct-drive spindles, this is not the case. Ramping up and down with a direct drive-spindle happens at a high rate, and the positional accuracy also is high, a significant benefit when using C-axis travel on live-tooling machines.

Source: Buying a Lathe: Spindles and Tailstocks

A built-in, numerically controlled tailstock can be a valuable feature for automated processes. A fully programmable tailstock provides more rigidity and thermal stability. However, the tailstock casting adds weight to the machine.

There are two basic types of programmable tailstocks — servo-driven and hydraulic. Servo-driven tailstocks are convenient, but the weight they can hold may be limited. Typically, a hydraulic tailstock has a retractable quill with a 6-inch stroke. The quill also can be extended to support a heavy workpiece, and do so with more force than a servo-driven tailstock can apply.

Source: Buying a Lathe: Spindles and Tailstocks