The secret of hard milling has been around for awhile. The problem is that people often don’t want to accept the requirements because of the necessary investment.You can’t take any shortcuts and expect to get results.

Hard milling is placing the CNC machine and the cutter in the worst type of cutting condition, so you must have all of the best solutions in place to counteract this. You must have a CNC machine with a rigid enough spindle to minimize vibration; a high quality end mill with the proper coating for the application; the expertise and assistance of an applications expert from the cutter company to ensure that you use the correct speeds, feeds, step-over and step-downs required for the material/hardness: too small of a step-over or step-down can be just as detrimental to a good result as too high a value; a highly accurate and rigid toolholder; and, proper CAM software.

Much of the software for CAM started out as general-purpose software. Often times the company was a CAD company first that decided to add CAM software in an attempt to supply a one-stop shopping environment. The toolpath that is output is very inconsistent and inaccurate, which causes the CNC machine to run on a rough or ragged path as opposed to a smooth path, resulting in poor surface finish and premature tool wear.

The Human Aspect of Technology
One aspect of hard milling that is often ignored is human resources. The new information that the CAM department must now understand and apply with regard to cutting tools, lasers, probes, machine tool capabilities, CAM software options, etc. has grown tremendously, so a fresh, open-minded internal review of procedures and personnel in the CAM/machining departments is required to be sure that you are not stuck in the “this is the way that we have always done it” routine. Every employee must be educated to understand that global competition is real, and will require personal sacrifices for the good of the company’s profitability to retain the jobs that we have.

Cutting tools are now more specifically application-designed and coated. All employees involved in the process must understand the specific differences between the various types and coatings. Using a tool for an incorrect application easily negates having the other variables satisfied.

Lasers being added to the hard milling process have allowed the elimination of the human in the accuracy of picking up each tool. It also has allowed for in-process checking and replacement of the tool as required caused by chipping or wear. Understanding of how the laser functions—including the macros that are used to control the laser—is now necessary as well as its required maintenance.

The probe now used in CNC machines for measurement introduces another piece of hardware/software necessary to understand. It is used for in-process checking, and in some cases alteration of the setup or offsets to bring the part into specifications.
The CNC machine has continued to develop over the years, including a more user-friendly, computer-oriented control. As the capability of the control has increased, the users learning requirements have grown. It is difficult to add more abilities to any product without requiring more involvement and understanding by the user. If there is an option available, there may be a normal default that doesn’t need to be changed very often, but someone must understand what the option is for and when it needs to be changed.

CAM software follows the same lead as the aforementioned items. Software has been developed and improved over the years based on user requests and complaints. Many of the new options are added, but the original variation is left available because many users prefer the original output. At this point a user must make a conscious decision as to what he wants the setting to be in this circumstance. This forces the user to be aware of the second or third choices—what they are designed for—to make the appropriate setting before starting the processing. This is not a one item situation. It grows as new things are added and will continue as software upgrades are released. To be effective the user must be given time to study the new capabilities of new releases and realize in his own application where they fit.