In a lathe (CNC lathe, CNC turning machine), the workpiece spins around its axis, while the cutting tool does not spin. Lathe is referred to as “turning”, and is effective for making cylindrical parts. Common turning operations include drilling, boring, threading, ID and OD grooving.
1. Lathes vs Turning Centers
CNC lathe just strictly does turning; A CNC turning center has milling capability, Most people called it a lathe in the past, but as CNC became more popular and CNC turning Center has the addition of milling and sub-spindles, it evolved into a CNC turning center.
The main spindle end often includes a Morse taper. it’s driven by an electric motor.
The lathe bed is a base connected to the headstock such that the carriage and tailstock move in parallel with the spindle access. This movement is facilitated by bedways, which restrain the carriage and tailstock in a set track.
(3) Feedscrews and Leadscrews
The feedscrew is a long driveshaft that connects to a series of gears in the apron in order to drive the carriage along the Z-axis. The leadscrew has the same function but operates orthogonally to the feedscrew, moving the carriage along the X-axis. Feedscrews and leadscrews are manufactured to either imperial or metric standards, which can cause compatibility issues between workpieces made on different lathes.
The carriage holds the cutting tool and moves it longitudinally to the workpiece for turning operations or perpendicularly for facing operations. The carriage is composed of two castings: the top, or saddle, and the side, or apron.
The tailstock refers to the center mount which is positioned opposite to the headstock. In contrast to the headstock, the spindle in the tailstock—which can include a taper to hold drill bits, centers or other tooling—does not rotate. Instead, it travels longitudinally under the action of a leadscrew.
2. Turning Center Operations
There are many operations that can be performed on a lathe, and even more that can be performed on a turning center. Here are some of the most common:
Facing operations are used to produce flat surfaces on the end of a part.
Threading operations produce external or internal threads on a part.
Knurling operations are used to produce a regularly shaped roughness on cylindrical surfaces.
One of the most basic operations, drilling is used to generate holes in workpieces.
Boring involves enlarging a hole or cavity to produce circular, internal grooves.
Reaming operations involve sizing and finishing existing holes.
(7) Taper Turning
In taper turning, the diameter of the workpiece is gradually reduced over the length of the part.
3. Horizontal Turning vs. Vertical Turning
CNC turning centers come in either horizontal or vertical configurations. There are also inverted vertical turning centers, which reverse the position of the spindle and the chuck. All three machine types generally consist of the same basic components (i.e., headstock, carriage, etc.), but differ in their orientation. Deciding whether to opt for a horizontal, vertical or inverted vertical lathe depends on a host of factors, but there are some rules of thumb that can help you make the decision.
The advantage with a horizontal lathe is that gravity pulls the chips away from the part.
4. CNC Turning Applications
CNC turning centers today are used in most metal cutting environments—whether it’s automotive, aerospace, agriculture,.
CNC Turning: Bottlenecks and Mistakes
In manufacturing, mistakes and bottlenecks in efficiency are to be avoided at all costs. This holds true even for a technology as old as the lathe, though the advent of computing in manufacturing has gone a long way toward minimizing these issues.
Bottlenecks for CNC Turning
One of the major limitations on lathe efficiency lies in the turning operation itself. This is not an issue that can be overcome with better tooling.
Machine tools are always trying to catch up to tooling capabilities. You might be able to cut at X amount of surface speed, but I can’t spin my chuck fast enough to generate that kind of surface speed. With turning, your rpm is limited because of chuck grip capabilities. The centrifugal force means that as the chuck is spinning around, the jaws want to move outward. On a machining center, the part is stationary and my tool—which is very compact—can be spun at 10, 12, 20 or even 40,000 rpm without big issues. There’s no way you can spin a chuck at 40,000 rpm; it would just come apart.
Another bottleneck for turning efficiency is one which applies to most manufacturing processes: changeover.
CNC (computer numerical control) tools such as lathes have become a vital part of manufacturing in a wide variety of industries. With a CNC lathe, you can easily produce complex parts that would be very difficult to machine on a manual lathe. A CNC lathe still requires significant skill to operate properly, but you can learn basic CNC machining techniques with the right training and practice. Below are some tips for newer machines.
Tip 1. Load the part program into the lathe if it is not already there. On newer machines, use a USB drive to transfer programs from a computer to the machine. With old machines, you may need to use a serial connection to the computer or even a 3.5-inch floppy disk.
Tip 2. Load the workpiece into the lathe. Make sure the chuck or collet has a tight grip on the workpiece.
Tip 3. Load the necessary tools into the lathe. The tools you will need for a given program, as well as the turret slots in which they should be placed, will have been determined at the time the program was written. If you will be using a program you did not write, consult the programmer if you have any questions about which tools to use.
Tip 4. Turn on the coolant pump and move the nozzle so the coolant stream is hitting the tip of the tool. Repeat this step for each tool.
Tip 5. Set the tool offsets. Slowly bring each tool toward the tool setter on the lathe until you hear a beep. Record the tool's position in the tool offset screen under the appropriate tool number. Repeat this procedure to set the X and Z offsets for each tool. For some programs, you will also have to record the tip radius of certain cutting tools in the tool offset screen. The tip radius should be found either marked on the tool or in the documentation for the tool.
Tip 6. Set the work offset. Rotate the turret to one of the cutting tools for which you have set the tool offset. Start the spindle and manually jog the cutter so that it faces off the end of the workpiece, leaving a smooth surface. Record the tool's position under the Z-axis work offset.
Tip 7. Run the part program. Watch the machine to make sure the program works as intended. Be ready to stop the machine immediately if something goes wrong.