PC based CNC machine tool controllers are starting to become the trend in CNC machining. Retrofitters and OEMs are looking toward the PC as the new machine tool controller platform to accommodate today's need for "high-speed" machining. More and more retrofitters and OEMs are starting to switch from a pre-fabricated controller to a PC based CNC controller for a variety of positive reasons. The most common reasons are described below.

PC based CNC machine tool controllers are less expensive than pre-fabricated controllers. You can replace your existing pre-fabricated control with a PC based controller at a fraction of the cost when compared to replacing your control with another pre-fabricated controller. This cost savings is accomplished because a PC based CNC controller uses a standard Windows based 95, 98, ME, NT or 2000 personal computer, motion control board, digital I/O card and CNC machine tool control software, which are relatively inexpensive components.

If you don't want to build your own PC based CNC machine tool controller, you don't have to. Today, there are several different companies manufacturing various ready-to-go, bolt-on professional PC based CNC controller enclosures. Most of these controller enclosures include all the hardware and software necessary to control your machine including the amps and motors. Users can also purchase separate high-quality hardware and software components and use their own personal computer.

PC based CNC machine tool controllers are easy to install. The idea behind advanced PC based CNC machine tool controllers is to eliminate the need for tracing wires to the PLC or write ladder logic. Rather, the computer becomes the PLC and does the logic thus eliminating the need for PLCs and writing ladder logic. PC based CNC machine tool controller software generally comes equipped with several ready-to-go operator screens to choose from and even customize for ease of use and to get you up and going in minimal time. The software generally allows you to mix and match physical buttons, knobs, gauges, switches, lights and displays with virtual ones.

PC based CNC machine tool controllers are also easy to use. A well designed PC based CNC controller software package generally has the ability for a user to fully customize the control's user interface without being a C++ or VB programmer. For example, the control's user interface is able to be designed by dragging and dropping control objects around the operator screen and then setting each control object's size, caption and functions with fill-in-the-blank or check boxes within Windows. The user interface can be as simple or as feature rich as the operator desires. Control operators are no longer subject to the rigid design of pre-fabricated controllers. PC based CNC machine tool controllers also offer various programming styles such as G code, conversational or CAD to motion.

PC based CNC machine tool controllers are quickly retrofitted. Most companies cannot afford to take months off to get a machine on-line and productive. A good PC based CNC machine tool controller's learning curve is only about 1/5 of the time needed when compared to most controllers that still use PLCs. On average, installation is capable of being done in three days for the most common types of knee mills, bed mills, lathes, lasers, water jets, plasmas and punch presses.

PC based CNC machine tool controllers are capable of stilling running a customer's old G code programs. A state-of-the-art PC based machine tool controller, for example, allows flexibility to run a Fanuc G code program in the morning and then an Allen Bradley in the afternoon. Definable G code and M code tables are generally built into the control to allow configuring the new controller to understand pre-existing programs.

Real time solid modeled or wireframe tool path simulation while the machine is cutting is one of the features a good PC based CNC machine tool controller contains. Being able to perform tool path animation and CNC verification prior to pressing Cycle Start is also an important feature. Simulation provides step-by-step control over each move graphically, moving the light source, solid model rotation and viewing angles.

PC based CNC machine tool controllers are user customizable and are considered an open system. The best software allows screens to be customized without having to be a VB or C++ programmer. Typical Windows-style fill in the blanks and check boxes are used on well-organized screens so that even novice Windows users can drag and drop objects into place and set their properties. More advanced users are able to configure the controller routines to support new processes and new technologies with well-documented software application program interfaces (APIs) made available to all customers as well as source code for ActiveX and DLLs.

All good software supports the ability to integrate third-party applications. PC based CNC machine tool controller software contains, at a minimum, machine maintenance software, remote diagnostics via a modem, self-diagnostics and remote machine tool monitoring via RS232, ActiveX or a Network card. This includes automatic collection of manufacturing data in real time without operator intervention as a standard feature.

PC based CNC machine tool controllers are fast and can easily accommodate today's "high speed" machining requirements. With over 200,000 motion cards shipped to date these cards can achieve 62.5 microsecond servo update times per axis, which result in cutting feedrate velocities of up to 122,000 IPM. Some digital I/O cards can detect a change of state at rates in the 10 KHz range. DSP microprocessors close the servo loop using dual 32 bit micro processors to increase productivity, feedrates, accuracy and cut quality. Multiple events and multiple position motions can happen simultaneously. 3D profiles can even be cutting while the tool is changing. The extra processor on the motion card is not only the best way to close the servo loop with the motors, it is also the fastest method known to date to produce the fastest block-to-block cutting speeds.

With PC based CNC machine tool controllers, maintenance and repair are no longer an issue. Machine operators are now the masters of their own machine. Self-diagnostics are generally a part of every system. When it comes to parts, off-the-shelf Windows 95, 98, ME, NT or 2000 personal computers and brand name hardware purchased from local sources can be used. Are your parts now either so proprietary or hard to find that they do not exist anymore? How long can you be down? PC based CNC machine tool controllers eliminate the need to rely on others. Machine operators can learn how to service, support, maintain and upgrade the complete control and replace any part themselves.

PC based CNC machine tool controllers help eliminate downtime. No more waiting for proprietary parts that can only be obtained through the control's manufacturer. Generally, there is a terminal strip and cable that connects the machine wiring to the computer. All that needs to be done is to unplug the cable from the computer. This will not disturb the wiring to the machine. Next, restore the screens, G codes, M codes and logic files within 10 seconds from a saved backup on a floppy disk. The backup file is also small enough to be emailed. If the problem is the motion or I/O card, either of these can be replaced by anyone without disturbing the wires. If a control breaks, swap out another computer to replace any control for any machine type at anytime.

PC based CNC machine tool controllers are easier and quicker to service. Manufacturers of PC based CNC controller software hire qualified technicians to immediately answer technical questions via phone, fax or email. If application assistance or custom logic is needed, the PC based CNC controller software manufacturer has qualified in-house staff and local reps that can fulfill these needs either on-site or via the internet. Also, most PC based CNC machine tool control software manufacturers do not detach themselves from the hardware boards and takes responsibility for all of the hardware boards they sell.

PC based CNC machine tool controllers allow use of your existing motors and amplifiers. This holds down the cost and labor plus ensures that the motors and amps are sized right for the machine. Good hardware can control existing motors that are: Brush or brushless, AC or DC, servo, stepper, PWM or hydraulic. The amps or drives can be either current driven or velocity type. Spindle drives use current mode or inverters. Feedback can be closed or open loop. Closed loop systems use encoders or resolvers. There are a number of companies that also make digital I/O cards. Touch screens are also available.

If you need a machine that will improve your speed and accuracy then try a CNC machine when you are getting large jobs done or doing very repetitive tasks. You can get a used one for half the cost of a new one since most individuals wouldn’t want to spend their money on a new one. CNC equipment can be found in woodworking shops or industrial settings. Add them to your collection that includes a milling machine as well.

If you need to drill holes than consider a CNC router. Some of them can hold more than one tool too. This makes it possible to do more than one procedure at a time. This will help you cut back on the tie you spend working and help you become more accurate.

Computer Numerated Control is the full name for CNC. In the 1970’s this technology was first created. These machines are easy to run and operate after they have been initially set up. They also need to be set up correctly and programmed before they are operated.

They can be made so you can drill a hole automatically. This can be much more accurate and quicker than manual drilling. You will get more uniform results. If you have a large job that needs a lot of drilling then this can be a good choice for you. You might get more inconsistent results when you are doing manual drilling and if the operator gets tired.

If you want a good thing to cut wood with then try a CNC lathe. You can buy one that ranges from 15-40 horsepower. You will choose the lathe power you need depending on the type of wood you use. You can get a model that comes with more than one mode. You can one that is totally manual or CNC. You can rig each machine for your individual project.

If you want the best in milling technology then try a Bridgeport mill. You can find a mill in both a small shop or a large one. If you want a mill that will last forever than try a Bridgeport mill. They are very pricey and more so than most people can afford.

A CNC mill use a special type of instrument that uses a combination of robotics and computer programming. You will get great results better than anyone could ever want. These are the kind of mills that the airline companies use. The CNC decides which tool is need for an operation and changes as it goes.

Since CNC equipment is so pricey it means most people can’t afford it. If you get a used machine you may find that you can afford it. You may be able to save about half on a used machine compared to a new one.

All CNC programs must be verified. While new programs present more challenges than proven programs, operators must be careful and alert during every step of a program's verification.

Step 1: Verify the correctness of the CNC program. This step is required for new programs or for programs that have been modified since the last time they were run (possibly because of engineering changes). It is also necessary to do this step if there is any doubt as to whether you are working with the current version of the program (after making changes at the machine the last time the job was run, perhaps the setup person forgot to save the program).

The objective of Step 1 is solely to confirm the correctness of motions commanded in the program. Other potential problems will require further verification at the machine; however, when Step 1 is successfully completed, the setup person will have confidence in the motions made by the program.

Some operators perform this step on the CNC machine during setup, which requires time. Many current model CNC machine tools have built-in toolpath displays, and as long as you verify the new program while the machine is running, you won't interfere with production. Not all CNC machines allow you to view one program's toolpath while another program is running. In this case, Step 1 will add to the setup time. If mistakes are found, the time it takes to correct them will also add to setup time.

Not all CNC machines provide toolpath display, and it is difficult to see a program's true motions by watching a CNC machine run a program. You may not be able to achieve the objective of Step 1 in this case because there might be serious mistakes to be found and corrected in Steps 2 and 3.

With the affordable off-line G-code level toolpath verification systems available, Step 1 can be performed for upcoming jobs, while the machine is running production shortly after a CNC program is created or modified. With these desktop computer-based systems, users can gain a better view of the program's movements than they could by watching the machine move.

If using an off-line system, the programmer is usually responsible for this step. They will perform this step shortly after the program is created. While most CAM systems have toolpath verification that is done as the CNC program is created, if changes are made to the G-code level program, many CAM systems cannot display the changes.

Even if changes are not made to the G-code level program, I recommend using a G-code level off-line program verification system to check the program's motions. If nothing else, this gives the programmer another way to see the motions a program is going to make before it is run on the CNC machine.

It takes a watchful eye to catch mistakes with an off-line system. Because the job is not currently on the machine, there is no real urgency, so mistakes can slip by. It might help to have someone else perform this step (another programmer or a setup person). Because the original programmer is so familiar with the job, he or she might not catch obvious mistakes. A setup person can be the best bet, since he or she will be responsible for actually running the program at the machine.

Many off-line systems don't show the location of clamps and other obstructions, so the person verifying the program must be able to visualize the placement of workholding components around the workpiece. The more problems they catch, the fewer problems there will be for the setup person to find and correct.

There may still be problems with the program's motions alter Step 1 is completed, but these problems should not be severe. Even with a toolpath display, it can be difficult to catch small motion mistakes. Some solid model-type program verification systems allow performing measurements on the virtual workpiece machined in the system; however, you must suspect that a problem exists before taking a measurement. For instance, with a mistake of less than 0.01 inch, it is likely that you may not suspect that anything is wrong.

After completing Step 1, the setup person can proceed to Step 2, which will be explained in next month's column. They must still be extremely careful, but there will be no big problems in the program's motions.

It's no secret that CNC retrofits of older 1 to 5 hp manual machine tools increase productivity and profits for machine shops. By automating manual operations, a CNC retrofit typically turns out parts 75 to 300 percent faster than a manual machine. It also assures repeatable accuracy; makes complex parts more easily; and reduces scrap, rework and manufacturing costs.

In function and price, a CNC retrofit for a manual mill fills the gap between a $2,000 digital readout (DRO) retrofit package and a $50,000 to $60,000 two-axis CNC milling center, but increasing capabilities of newer CNC retrofits are narrowing the gap between them and new machines.

For instance, a CNC retrofit control package recently introduced by Mitutoyo/MTI Corporation (Aurora, Illinois) approaches the functionality of a low horsepower CNC milling machine at about one-fifth the cost. Called MILLSTAR, this CNC retrofit package includes a control with Windows 95 compatibility, choice of shop or G-Code program language, advanced geometry calculations, and glass linear scales. According to MTI, it enables a manual mill to turn out low to medium volume work at the same rates as a full CNC milling machine of equal spindle horsepower.

Connectivity to Windows 95 software makes programming user-friendly and intuitive for machine operators, freeing operators up for more complex jobs. This helps shops cope with the skills shortage, especially programmers, and the need for operators to program on their own. Shop and G-Code language, likewise, facilitate programming by operators. Part prints in G-Code can be downloaded directly to create the program, saving time and eliminating another error source.

The company reports that high-precision glass linear scales provide better positioning accuracy than rotary encoders: This is why they are offered as extras on many CNC retrofit packages and built-in controls. The difference becomes especially important on older mills where there may be more play in the table ways. Positioning repeatability of a retrofit CNC control with glass linear scales matches that of the controls on a full CNC milling machine.

This retrofit package includes servo-motors with adequate power to move the table at optimum feed rates for heavy cuts, even on large 5-hp manual mills. Because the CNC part programs will be calling for higher material removal rates than are customary for manual work, under-powered servomotors are likely to hold the operation back.

A DRO-equipped machine provides no such automatic table movement, but rather clear, more readable positional readings. The operator must dial in table feeds and stops, and start each cut as if on a manual mill; there is still a possibility for error.

Advanced geometry calculation saves both programming and running time for complex shapes including angles, radii, and irregular pockets. During programming, the operator inputs the known linear and curved measurements and designates the type of cut. No calculations are necessary on the part of the operator. The machine's geometry calculator computes the unknown measurements and the required tool path. During operation, moreover, complex cuts are made at the same removal rates as simpler cuts. The control "thinks" fast enough to keep the cutter running at full speed. If a shop's work involves a lot of circles, hole patterns, arcs and pockets, the additional programming efficiency of canned cycles may justify a retrofit.

Large memory for routines means that routines can be retrieved and used on another job. The larger the memory, the more routines available for the next job. The MILLSTAR's memory can store hundreds of routines, depending on their length. Similar parts do not have to be reprogrammed; only new dimensions need to be inputted. The system recognizes the part and updates the routine with the new data.

Manual override enables the operator to run a one/off or prototype job as usual. Where there's an applicable routine or subroutine, the operator can pick it up from memory. Where something unique to the part needs to be done, the operator switches to the manual mode, makes the cut, and returns to program mode.

The benefit of thee-axis readout in a two-axis CNC retrofit is precise control of height/depth at lower cost than full three-axis control. The company is launching a three-axis CNC control at IMTS 98. However, current two-axis units will be upgradable to three-axis control.

Owners of old manual milling machines confronted with today's capacity crunch have at least three choices for increasing throughput without buying a new CNC machining center. They can retrofit an existing mill with a CNC control package or a DRO, or they can buy a new manual mill with a CNC retrofit package in place from the outset. MTI reports that a substantial number of MILLSTARs are going onto brand new manual mills.

CNC retrofit packages vary widely in capability, standard features, extras, and cost. Each shop's choice should be dictated by specific requirements including workload and its complexity, volume and lot size, delivery requirements, and availability of capital and skilled labor. It is a good idea to spend no more than you can recover in a year out of increased throughput and labor savings in programming and chipmaking.