Considerations for a New CNC Machine

Here are five factors you shouldn’t overlook.

When you evaluate CNC machine tools to determine which would best suit your needs, there are surely countless factors that will affect your buying decision. Rapid rates, axis travels, spindle horsepower and cutting tool capacity are but a few of the many criteria that will help you determine whether a given machine will do what you need it to do—based on the price you are willing to pay.

Once you make the buying decision, you likely set about ensuring that the machine will hit the floor running. You order cutting tool components, workholding, accessories, fluids and anything else you will need once the new machine is delivered. The following are five considerations that tend to get overlooked in a new machine installation, however. While they would probably not affect your decision to buy a given machine, they can have a big impact on long-term machine utilization.

1. Power curves for the spindle drive system. All machine tool builders specify spindle horsepower as part of their standard quotations. This is usually a duty rating, meaning the motor can output the specified horsepower for a given percentage of usage time per hour. It is important to know that the spindle cannot output maximum horsepower and torque at all rotational speeds. Generally speaking, the faster the motor runs, the greater the available power. 

For this reason, builders often provide multiple spindle ranges to increase power output at lower motor speeds. This can be done using some kind of transmission gearbox or with multiple coil windings on the motor. Spindle-range changing can be somewhat transparent. With many machining centers, for example, it is done using an S word, without requiring a special programming command. Thus, some programmers may not even know that a machine has multiple spindle ranges.

Of course, in order to make the best use of a machine, you must know how much power is available throughout the various speeds in each spindle range. Surprisingly, power curve information may not be as readily available as you might think. Some machine builders include a power curve graph in their programming manuals. With others, you may have to make a special request.

2. List of recommended spare parts. Hopefully, your brand-new CNC machine will run for a long time before anything wears out. Even so, you must be prepared for eventual failures. Your machine builder and control manufacturer should be able to provide a list of components that are most prone to failure and specify those components that will most likely break during a mishap (crash). Common examples include batteries for memory and absolute encoder position backup, filters, fluids, and taper alignment pins. Don’t wait until something fails before ordering a replacement. Instead, maintain a complement of recommended spare parts for the time when they are needed. 

3. New or different maintenance procedures. It is likely that any new machine will include new features and functions that require your maintenance personnel to do some things differently. For example, you may be buying your first machine that has absolute pulse coders on axis drive motors. These motors require a battery to maintain position while the power is off, and a special (different) procedure to reset the home position should it be lost for reasons such as battery failure or crash. The time to prepare for these new procedures is while the machine is new, before the procedure is required.

4. Memory backup. I’ve said this many times before: You must know how to create backup copies of all data stored with the CNC. This is especially true with a new machine. Backing up common usage data like CNC programs and offset settings may be part of your company’s standard operating procedure, and you likely have a direct numerical control system to save CNC programs for repeated jobs. For maintenance purposes, you must create backup copies of all other data as well. This data includes CNC parameters, custom macro variables (if your machine has a touch probe), the programmable machine controller (PMC) ladder program and PMC parameters.

5. Confirm some basic usage settings. If you have other machines that are similar to the one you are buying, you will probably want to use similar (or identical) operational techniques. You must first know if any initial settings are dramatically different on the new machine, however. ]

The set of initialized states, that is, modes automatically instated during power-up, should be the same for all of your machines. For example, you will not want some machines powering up in the metric measurement system while others power up in the imperial (inch) measurement system. One severe complication is related to decimal point entry or, better said, what happens if a value is entered without a decimal point. Typically, on older machines, if you enter a value of 20 (no decimal point) in the imperial system, the CNC will interpret the value as 0.0020 inches. Newer CNCs provide a setting choice (commonly called calculator input) that determines what happens if a value is entered without a decimal point. With these CNCs, it is possible that a value of 20 (again, no decimal point) will be interpreted as 20.0 inches.