or unloading of workpieces with the spindle stopped.
• Follow recommended safety policies and procedures when operating machinery, handling parts or tooling, and lifting.
• Make sure machine guards are in position during operation.
• Keep wrenches, tools, and parts away from the machine’s moving parts.
• Make sure fixtures and workpieces are securely clamped before starting the machine.
• Inspect cutting tools for wear or damage prior to use.
Don’ts:
• Never operate a machine until properly instructed in its use.
• Never wear neckties, long sleeves, wristwatches, rings, gloves, or loose long hair when operating any machine.
• Never attempt to remove metal chips with hands or fingers.
• Never direct compressed air at yourself or others.
• Never operate an NC/CNC machine without first consulting the specific operator manual for the machine.
• Never place hands near a revolving spindle.
• Electrical cabinet doors are to be opened only by qualified personnel for maintenance purposes.
A large investment has been made to purchase CNC equipment. It is very important to recognize the need for proper maintenance and a general upkeep of these machines. At the beginning of each opportunity to work on any turning or machining center, verify that all lubrication reservoirs are properly filled with the correct oils. The recommended oils are listed in the operation or maintenance manuals typically provided with the equipment. Sometimes there is a placard (plate) with a diagram of the machine and numbered locations for lubrication and the oil type is found on the machine. Most modern CNC machines have sensors that will not allow operation of the machine when the way or spindle oil levels are too low. Pneumatic (air) pressures need to be at a specified level and regulated properly. If the pressure is too low, some machine functions will not operate until the pressure is restored to normal. The standard air pressure setting is listed in pounds per square inch (PSI) and a pressure regulator is commonly located at the rear of the machine. Keeping machines maintained and in their optimum health is required to avoid costly failures and ensure maximum productivity. Check with your company and follow their Total Productive Maintenance (TPM) program. Refer to the operator or maintenance manuals for recommended maintenance activities.
Coolant Reservoir
The coolant tank level should be checked and adjusted as needed prior to use. A site glass is normally mounted on the tank for easy viewing. Use an acceptable water-soluble coolant mix, synthetic coolant, or cutting oil. Periodically the coolant tank should be cleaned and refilled. The coolant PH level should be checked routinely with a refractometer; the mixture should be adjusted in order to prevent bacterial growth. When synthetic coolants are used, the coolant system may stay clean longer.
Because machine slide-ways need constant lubrication during operation, automatic oiler systems inject an appropriate amount of oil at intervals determined by the builder. There is almost always excess oil that finds its way into the coolant system. Because of this condition, companies employ the use of add-on oil skimmers designed to clean the coolant. The “tramp oil” must be removed and discarded properly. Some new machine tools are incorporating sealed lubrication systems to help alleviate this problem.
Daily Maintenance Activities
Do’s:
• Verify that all lubrication reservoirs are filled.
• Verify air pressure level by examining the regulator on the machine.
• Check that the chip pan, coolant level, and mixture are correct; clean or fill, as needed.
• Make sure that automatic chip removal equipment is operational when the machine is cutting metal.
• Be sure that the worktable and all mating surfaces are clean and free from nicks or burrs.
• Check to see that the chuck pressure setting is adequate for clamping the work to be machined.
• 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