The term "CNC turning center" applies to several types of tooling machine which is more advance than an ordinary machines or the manual machining. Unlike before machines are now becoming more sophisticated that every processes shall be operated by programs with high accuracy and precision. This type of machines works well and faster than that of he previous tooling machines.
Let's take a closer look to the features of these machines:
Bar machine-These units are capable in the preparation of the bar stocks ready for machining. They are ideal for short and long runs and allow quick setups and changeovers. Typically, automatic feeders are standard on bar machines, so you can place large bundles of pipe, tube or bar stock in the feeder and run the machine unattended if desired.
see www.topbarfeed.com
Swiss type CNC machine- This type of machine uses a sliding headstock with stationary tooling to machine parts. A bar constantly feeds out of the spindle as a stationary cutting tool removes metal. By cutting as close to the spindle as possible, maximum workpiece and cutting tool rigidity are maintained. The Swiss type machines typical has faster revolution of spindles and greater feed rate performance . Therefore, certain parts can be machined more efficiently than on a traditional CNC turning center. Good turning center must have parts of the least diameter and four times longer than their larges diameter.
see www.eurotechelite.com/newFrame_tss_15~.htm
Slant-bed turning center. The slantbed machine is a high-performance unit—a marvel of technology. It offers positioning accuracy and repeatability in the millionths of an inch, with rapidtraverses exceeding 1,100 ipm on several models. In addition, some units come with 30-, 40- or even 50-hp spindles. They can rotate a workpiece at up to 6,000 rpm, depending on chuck size. Standard acceleration is from zero to full-rapid in 0.01 sec., with the turret indexing in less than 0.01 sec.
Slant-bed turning centers allow fast setups by incorporating precision turrets and indexable tooling. The turrets have eight to 12 tool positions and accommodate both ID and OD tools. The slant beds generally have a larger turning diameter than the same size flat-bed machine.
Twin-spindle turning center. This version of the slant-bed turning center is designed for longer production runs and is especially useful when machining the faces and backsides of parts. Upon completion of the first operation, the sub-spindle—instead of a tailstock —moves forward with its chuck in the open position and clamps onto the part. The main spindle releases the part, which is retracted to its new machining location. The rear of the part is then machined. This type of setup reduces operator intervention. 
Twin-spindle/twin-turret machine. Similar to the twin-spindle arrangement, this type of turning center has a second turret that allows you to simultaneously machine both ends of a part.
Turn/mill center. This machine, also known as a turning center with live tooling, was designed for part runs of 100 to 1,000. It may be equipped with a C-axis or Y-axis for cross-drilling, keyslot milling, producing bolt-hole patterns and other operations. It can produce very complicated parts.
Depending on the part configuration, a turn/mill center can eliminate secondary operations. It comes with a hefty price tag, though, so it is not for the faint of heart. These units can be very efficient and lead to high profits, but the performance-to-cost return should be weighed carefully. And, successful operation of a turn/mill center requires a functional knowledge of machine tool programming language.
Because of this requirement, turning center builders offer training in conversational programming, G-code programming and offline programming systems. Most builders, because of the level of machine sophistication, recommend up to a week of training at their facilities. Additionally, some include training in the base price of the unit; others sell it as an option. Of course, the buyer covers travel, hotel and meal expenses for trainees.
CNC lathe options
Choosing the right option(s) for your CNC lathe is another important aspect of machine selection. Some of the most common add-ons builders offer are described in the following paragraphs.
Chuck. Most CNC turning centers come with a standard chuck. It may be a collet chuck or a simple hydraulic, 3- jaw chuck. Other types of chucks are available.
Bore size. Most CNC turning centers come with a standard through-hole. The size is dependent on the manufacturer. Bores larger than standard are usually available. Touch probes deserve serious consideration. Some machine builders include them as standard equipment, especially with production CNC turning centers. As the touch probe swings in, the operator jogs the tool to the probe in the X and Z axes. Then the touch probe transmits tool length and diameter offsets to the controller, automatically eliminating any operator error. On some turning centers, the operator simply inputs what tool he wants and the rest will be done by the machine program and its tooling part.
Live tooling. Live tooling allows crossdrilling, key-slot milling, milling flats and so forth—the normal operations of the machining center. The motors that drive the live tooling can range from 4.5 hp to 7 hp or higher. They have a relatively low rpm and torque.
Tailstock. Although some manufacturers consider tailstocks to be standard items, they probably rank at the top of the list of options for both combination lathes and CNC turning centers. They are available in several versions: manual tailstock with manual quills, manual tailstock with programmable quills, programmable tailstock with fixed quills and programmable tailstocks with programmable quills. 
