Clean up the machine at the end of use with a wet/dry vacuum or wash machine guards with coolant to remove chips from the working envelope.
Most new CNC machines are equipped with guards that envelop the worktable. The guards protect the ways and sensitive micro-switches installed as limit switches for table movement. Guards also help keep the surrounding floor space clean, but there is still the task of chip disposal. Some larger production machines incorporate a chip conveyor, which carries the chips to a drum on the floor on either side of the machine for easy removal. Even with these features, there is still a need for chip cleanup inside the working envelope at least once a day. If chips are allowed to gather within the guards, they will eventually find their way around the guards that protect the machine ways. Over time, some of the chips might become embedded into the ways and cause irreparable damage.
Another problem that may occur as the chips collect is that they bunch up and are pushed into contact with the micro-switches. This contact stops the machine from working because the switches send a signal to the control that indicates table travel limit has been exceeded. This message prevents the machine from operating until the chips are removed. If chips get within the guards around the micro-switches, it is necessary to remove those guards and clean. If this extent of cleaning becomes necessary, the machine should be turned off and a Lock-Out/Tag-Out should be incorporated to prevent injury. Remember: it is essential to replace the guards after cleanup.
It is very important to thoroughly clean the machine when many chips are present. The exterior of the machine usually will need only wiping down with a clean rag. You can clean the ways and the working envelope without damaging the machine by using coolant to wash the machine table and the guards free of chips. Another effective cleaning method is to use a wet/dry vacuum to pick up the chips. Along with the chip conveyor system, these two methods have proven hard to beat.
It is NOT recommended that you use compressed air to blow away the chips from the ways. It is, however, appropriate to use compressed air to remove chips and coolant from the workpiece itself or work holding fixtures such as a vise. The problem with using compressed air to clean up around the ways is that when chips are blasted away from the table, many are forced behind the guards, further worsening the micro-switch problem described above.
Last but not the least important is the cleanliness of the worktable, tools, and area. Be sure to clean off any metal chips and remove any nicks or burrs on the clamping or mating surfaces. Always clean the machine after use.
Proper selection of cutting tools and work holding methods are paramount to the success of any machining operation. The scope of this text is not intended to teach all of the necessary information regarding tooling. You must consult the appropriate tooling catalogs, websites, and online resources for selection of tool holders and cutting tools that are relevant to the required operation. Least expensive is not necessarily best.
Sound machining principals require that the most rigid set-up possible be used that does not allow large overhangs of tools or workpieces. Ignoring these basic principles can cause tool and workpiece deflection and vibration that will contribute to poor surface finish and, eventually, tool damage, which also makes it difficult to maintain dimensional accuracy.
Just as with the rest of the machine tool, there are components used with the actual cutting tool that make it what it is. Obviously, the tool cutting edge is where the metal removal takes place. Without proper tool clamping, the cutting action may not produce the desired results. Therefore, it is very important to carefully select the most effective tool clamping method.
In the case of a simple operation of milling a contour on a part, we may select a collet or a positive locking (posi-lock) end mill holder for the end mill. The correct choice would depend on the actual features of the part to be machined and its dimensional tolerance. If the amount of metal to be removed is minimal and the tolerance allows, then a collet would probably suffice. But if a considerable amount of metal is to be removed (more than two-thirds of the tool diameter on a single depth of cut pass), then the posi-lock end mill holder selection is important. The reason for selecting the posi-lock holder is that under heavy cuts, a collet may not be able to grip the tool tightly enough. This situation could allow the tool to spin within the collet while cutting is in progress, with the result of ruining the collet and possibly damaging the part being machined. There is a tendency for the tool to dive into the workpiece when the tool spins within the collet and so damage to the part may occur.
Note: Most high speed steel (HSS) end mills have a flat ground on them to facilitate the use of the posi-lock holder. This flat area allows for a set-screw to lock into it, creating a rigid and stable tool clamping method. The clamping method for drills could be either a collet or a drill chuck. A keyed drill chuck usually is used for heavier metal removal or larger holes, whereas the keyless-type drill chuck is suitable for small holes. Generally, in the case of larger drills, a collet will be necessary to hold the tool. When holes are to be drilled, remember to center-drill or spot-drill first, so that the tool does not have a tendency to wander off location. The center-drill may be held in the same manner as a drill. For high volume/accuracy applications, hydraulic shrink-fit tool holders may perform best; when high rev/min are required, tool balancing is imperative for best accuracy.
For turning, the selection of the type of tool holder is determined by the finished part geometry and the part material. There are a variety of tool holder styles as well as indexable insert shapes available to accomplish the desired part shape and size.
For more information on the proper selection of inserts and tool holders, refer to the Machinery’s Handbook section titled “Indexable Inserts”.
Another valuable resource for technical data regarding the selection of inserts and tool holding are the ordering catalogs, online advice, and optimization applications from the tool and insert manufacturers.
Cutting tools are a very important aspect of machining. If the improper tool and/ or tool clamping method is used, the result will most likely be a poorly machined part. Always research and use the best tool and clamping method for a given operation. With the high speed and high performance of CNC machines, the proper selection process becomes increasingly important. The entire CNC machining process can be compromised by a lack of good tool planning and improper use.
There are many different types of machining operations performed on either turning or machining centers. The tool is where the action is, so if improper selection takes place here, the whole machining sequence will be affected. Years of study have been dedicated to this subject and are documented within reference manuals, buyer’s guides, and online applications. Using these references will be helpful for correctly choosing a tool for a given operation.
Remember that in your selection process you are searching for the optimum metal-cutting conditions. The best way to understand how to choose the proper conditions is by studying the available data such as: the machine capabilities; the specific type of operation; the proper cutting tool(s) and tool clamping method(s); the geometry of the part to be made; the workpiece and cutter material; and the method of clamping the part.
It is important to utilize the most technologically advanced methods of metal removal available. Do not hesitate to research this new technology. For example, in recent years, there have been numerous cutting tool innovations that include indexable insert coatings and materials such as: Titanium Nitride (TiN); Titanium Carbon Nitride (TiCN) applied through Chemical Vapor Deposition (CVD), or Physical Vapor Deposition (PVD); Ceramic; Cubic Boron Nitride (CBN); and Polycrystalline Diamond
