(PCD). These advances have enabled increased cutting speeds and decreased tool wear, providing for higher production throughput. Another tool clamping innovation is modular tooling. This is a standardization of tool holders to facilitate the quick change of tools, decreasing setup time. Refer to the tool and insert ordering catalogs and online applications from the tool and insert manufacturers for more information on modular tooling.
Important information about the tool must be given to the machine control unit (MCU) for the machine to be able to use the tool effectively. In other words, the MCU needs the tool identification number, the tool length offset (TLO), and the specific diameter of each tool. A TLO is a measurement given to the control unit to compensate for the tool length when movements are commanded. The cutter diameter compensation (CDC) offset is used by the control to compensate for the diameter of the tool during commanded movements.
The tool number identifies where the tool is located within the storage magazine or turret and often is the order sequence in which it is used. Each is assigned a tool length offset number. This number correlates with the pocket or turret position number and, in the case of a milling machine, is where the measured offset distance from the cutting tip to the spindle face is stored. For example, Tool No. 1 will have TLO No. 1. Finally, when milling, the diameter of the tool is compensated. In most cases, the programmer has taken the diameter of the tool into account. In other words, the programmed tool path is written with a specific tool size in mind. However, more commonly the part geometry is programmed in order to facilitate the use of different tool diameters for a specified operation. When using the part geometry rather than the toolpath centerline for a specific tool diameter, an additional offset is called from within the program called cutter diameter compensation (CDC).
In many cases today, tool presetting and tool management systems are used to accurately input the TLO and diameter data values via network connection to the machine tool. This prevents the incorrect data from being entered via the keyboard and does not use machine time for measuring. Tools are also often fitted with Radio Frequency Identification (RFID) chips that carry this information to the machine tool.
Figure 1-1 Milling Tool Holder Courtesy Kennametal
Figure 1-2 BT Tool Holder Courtesy Kennametal
CNC equipment enables more efficient machining by allowing the combination of several operations into a single setup. This combination of operations requires the use of multiple cutting tools. An automatic tool changer (ATC) is a standard feature on most CNC machining centers, while many CNC knee-mills still require manual installation of the tool. The illustrations in this section show types of tool holders used on CNC machines; they have distinct physical differences and all of the holders are tapered. In Figure 1-1, the tool holder has only one ring and is designed for machines that require manual tool changes. The tools in Figures 1-2 (BT), 1-3 (CAT), and 1-4 (HSK) are designed for machines that have automatic tool changers. The rings act as a gripping surface for a tool changer. The tapered portion of the holder is the actual surface that is in contact with the mating taper of the spindle. These tapers are standardized by the industry and are numbered according to size. Common sizes for CAT tooling are: No. 30, 40, and 50. Common sizes for HSK tooling are: 40, 50, 63, 80, and 100.
One benefit of these tapers over the standard R-8 Bridgeport style of tool holder is the increased surface area in contact with the mating taper of the spindle. The increased surface area makes the tool setup more rigid and stable. Big-Plus® style tool holders mate the taper and the flange to further increase the contacted surface area.
Figures 1-3 CAT Tool Holder Courtesy Kennametal
Figure 1-4 HSK Tool Holder Courtesy Kennametal
Another feature on the tool holder is the notch or cutout on the centerline of the tool (there is an identical cutout on the opposite side). These cutouts enable axial orientation within the spindle and tool changer. As the holder is inserted into the spindle, the cutouts enable it to be locked into place in exactly the same orientation each and every time it is used. This orientation makes a real difference when trying to perform very precise operations such as boring a diameter. These notches also aid the spindle driving mechanism.
On CNC machines with a manual tool change, the holder is inserted into the machine and rotated until the holder pops into place (axial orientation is done by hand). The draw bar is then tightened to clamp the tool holder in place. Finally, another component of the CNC automatic tool changing system is the retention knob or pull-stud (Figures 1-5 and 1-6). Machining centers need the retention knob or pull-stud to pull the tool into the spindle and clamp the holder. This knob is threaded into the small end of the taper, as shown. Note: There are several styles of knobs available. The operator should consult the appropriate manufacturer manual for specifications required in their situation.
Figure 1-5 CAT Tool Holder With Retention Knob Courtesy Kennametal
Many tool and work holding methods used on manual machines are also used on CNC machines. The machines themselves differ in their method of control, but otherwise they are very similar. The major objective of CNC is to increase productivity and improve quality by consistently controlling the machining operation. Knowledge of the exact capabilities of the machine and its components, as well as the tooling involved, is imperative when working with CNC. It is necessary for CNC programmers to have a thorough knowledge of the CNC machines they are responsible for programming. This may involve an ongoing process of research and training updates with the ultimate goal of obtaining a near optimum metal-cutting process. From this research and training come a decrease in the cycle time necessary to produce each part, thus lowering the per piece cost to the consumer. Fine tuning of the machining process for high-speed production gives more control over the quality of the product on a consistent basis. The following are some of the most important factors that affect the metal cutting process.
Figure 1-6 Retention Knob Courtesy Kennametal
The Machine Tool
The machine used must have the physical ability to perform the machining. If the planned machining cut requires 10 horsepower from the spindle motor, a machine with only 5 horsepower will not be an efficient one to use. It is important to work within the capabilities of the machine tool. The stability, rigidity, and repeatability of the machine are of paramount importance as well. Always take these things
