FactoryFix.com - CNC Machine Maintenance and Calibration is necessary to keep your expensive equipment functional for as long as possible. Here is your guide to the routines you should adopt to ensure your industrial CNC equipment lasts the longest.

1.
Whether you’re a job shop or contract manufacturer, it’s important to repeatedly check
in on your CNC machine tools are doing to protect your capital investment. Whether
you’re intending to maximize your capacity or simply protect day­to­day operations, both
CNC machine maintenance and CNC machine calibration are indispensable routines
that you need to stay true to.
Preventive maintenance is a mindset to protect your CNC machine tools, maximize
optimization and reduce downtime. On the other hand, calibration will be necessary to
ensure a high degree of repeatability on the shop floor. To boost your equipment
lifetime and ensure constant uptime, check out the guide below.
Step One: Understand Predictive
Maintenance Programs

2. Predictive maintenance programs, or PDM programs, are used to reduce machine
downtime and gauge project quality by anticipating problems before they happen. To
assure each machine tool’s maximum performance, today’s manufacturers are using
four major programs to streamline maintenance, repair and calibration:
● Reliability and Maintainability
● Machine Tool Variability Management System
● Failure Mode and Effective Analysis
● Total Productive Maintenance
These programs, when adjoined, can predict expertly when a CNC machine tool will
become intolerant, fail or require calibration. While calibration will be discussed further
down, maintenance will be focused upon first.
Step Two: Plan for Downtime Ahead of Time
Your workplace will need to plan for downtime to ​reduce​ downtime. During critical
production periods, you’ll need to monitor machine tools, collect data, utilize a
combination of industrial instruments and conduct analysis effectively. Data is your
friend! That being said, if you do not have a plan on how to collect and store data, you
can become overwhelmed with the numbers.
You’ll need to gather a historic collection of in­house data. This data, when used
alongside the above­mentioned programs, will greatly assist the maintenance process.
Vibration analysis, calibration metrics and infrared thermography equipment, too, will be
needed.
Your historic data comparison will be used to predict your CNC machines’ service
requirements. Different machines have different work scopes, and each should be

3. attended to, repair and maintenance­wise, depending upon pre­scheduled periods. In
doing so, your shop can limit production interference while conducting maintenance.
Step Three: Conduct Quick­Check Tests
Next, conduct quick­check tests on any machines in production. While industry PDM
programs are designed to reduce workplace downtime; weekly quick­check procedures
will reduce machine service time on a day­to­day basis.
Because of this, quick­check techniques will need to be integrated alongside your PDM
programs to assess, predict and reduce machine downtime. Some company’s
quick­check procedures involve measuring a machine tool’s ​overall volumetric accuracy
via laser­based measurements. If your company is using new laser calibration
machines, these checks can be performed without ever needing to remove a machine’s
components or covers.
Step Four: Outline Your Maintenance Plan
Before jumping into predictive or preventive maintenance programs, you should
understand the scope of the maintenance that needs to be performed. Everyone in the
company needs to be dedicated to ​preventive maintenance. Your maintenance plan
should include—but isn’t limited to—several different areas of focus:

4. Filter and Oil Changes
First, filters and oils should be changed regularly. Most preventive maintenance
programs entail additional steps during filter and oil replacement depending upon the
machine. This maintains a high degree of repeatability, extending equipment life while
ensuring ongoing operation.
Electronic Check­Up
Next, preventive maintenance will require a check­up via electronic diagnostic
monitoring tools. To perform a total CNC machine check­up, your in­house workers will
need to check electric motors, drives, cables, amps, HMIs, and any other electronics
involved with the machine. Each should be inspected and undergo repairs when
needed.
Step Five: Understand Predictive
Maintenance Drivers
Industry­wide adoption of PDM programs are norm these days. In fact, the growth is
largely driven from a migration from manual machines to CNC machine tools. Higher
production rates, higher quality requirements and fast­paced industry production all
result in an intensive need for ongoing PDM programs, and your shop needs to be a
part of this trend.
A regular PDM program will require a thorough inspection of each CNC machine tool
twice per year. During these check­ups, vibration analysis and overall micron­level

5. accuracy will need to be noted. After these are measured, the data will need to be
analyzed using the machine’s baseline data, previous­year data and newly acquired
data. Together, these data sets can create a “prediction” about a machine’s needed
maintenance, calibration, and any failure that could take place in the near future.
A Quick Return to the Quick­Check Technique
The quick­check technique, again, is relevant. It grants users knowledge of a machine’s
volumetric accuracy, giving diagonal displacement measurements of complex functions.
Again, if your workplace has adopted laser­based measurements, it can use the
quick­check technique to examine movement pattern tests. In these tests, a CNC
machine will reveal any errors in laser alignment. A laser’s linear position, reversal, yaw
and pitch can help you catch a potential failure early in the process.
Step Six: Creating Your Own Predictive
Maintenance Process
Every manufacturer needs a custom PDM process uniquely tailored to them to
effectively service their machines. CNC machines can be incredibly varied, and a
standard PDM process may fail in accommodating for all processes, all components,
and different types of machines.
Every PDM program, for this reason, requires a long creation process. Your own PDM
program will be comprised of many steps. These steps, firstly, will identify which CNC

6. machine’s tools will be incorporated in testing. Secondly, they will determine the
technologies needed to measure, monitor and derive data from machine tool operation.
Make sure your PDM program, above all, accommodates for the following:
● Vibration measurements
● Calibration measurements
● Infrared thermography measurements
● Data collection and analysis
● Cleaning and restoration
Step Seven: Selecting Predictive
Maintenance Equipment
You’ll need to select equipment worthy of your PDM process, too. Once your workplace
has purchased its needed equipment, it’ll be able to “mold” PDM procedures around it.
That said, every PDM program requires several elements—elements which should be
accessible to your purchased equipment. While equipment, itself, is as varied as a CNC
machine can be, you should take care in purchasing maintenance equipment able to
conduct the following:
● CNC machine diagnostics
● CNC machine tool condition monitoring
● Data analysis and corrective action creation

7. Overall, your predictive maintenance equipment will host several options to identify,
measure and create solutions to maintenance issues. Early warnings are ​absolutely
important, and your workplace’s full integration of its precision measurement programs
is vital to each CNC machine’s manufacturing longevity.
Once your workplace has identified its needed program procedures, it must establish
criteria around acceptable accuracy and performance. These standards will create a
“baseline of error” which will alert your team of potential issues. All machine tool
baseline conditions must be identified, and consistent machine measurements will need
to be taken on a periodic basis. By collecting data frequently, you can create a data
trend. This trend, when analyzed, will be your key to creating maintenance
predictions—and, as a result, predictive maintenance schedules.
Machine Tool Calibration
Predictive maintenance is incredibly effective. However, with the adoption of new
technology practical instruments capable of measuring machine tool performance have
become even more important. In previous years, a manual machine tool’s overall
accuracy was determined by its operator’s ability to turn crank handles accurately,
navigate with precision and ensure consistency. Statistically determining these
processes, of course, was impossible. Simply put: There was little way to calibrate or
determine a process’s capabilities.
CNC machines, however, needed verifiable positioning, high­end precision and error
compensation. New calibration tools were the answer. Early developed machine
calibration techniques relied upon mechanical artifacts and a comparator to measure a

8. CNC machine’s static accuracy. Even in controlled conditions, however, the comparator
faced issues from low resolution. For this reason, any calibration method conducted by
an operator still faces accuracy issues.
Using a Grid Plate Encoder to Calibrate
To conduct basic calibration, consider using a grid plate encoder. A grid plate encoder
features a spindle­mounted, non­contact reading head. This reading head scans a
targeted area with a circular path, measuring a grid plate as it’s mounted upon the
targeted machine table. During grid plate encoding, the head reveals plot deviations
from a circle. Often, these measurements refer to a true circle, so as to limit deviations
as much as possible. The head’s created plot, then, can be used as a guideline to
correct servodrive errors, machine mechanism deviations and other measurements. A
grid plate encoder, however, can only correct errors in two axes.
Using a Double­Ball Bar System to Calibrate
Dynamic path accuracy can also be measured with a double­ball bar system. A
double­ball bar system is a telescopic bar with a mounted ball upon each end. When
one ball pivots within the system’s socket—which is anchored to a table—the other
pivots within its spindle socket. As a circular path is created, any changes in distance
between the two mounted balls will reveal an error in circle perfection.
Using a Capacitor Gage to Calibrate

9. The capacitor gage, meanwhile, may be used to measure a spindle’s thermal growth, or
“runout.” While a capacitor gage won’t be useful for calibration in every machine, it’s
incredibly useful for calibrating prolonged spindle use when thermal growth may offset a
directed path.
Using a Rotary Encoder to Calibrate Rotary Motion
In most cases, your CNC machine rotary tables will need intensive calibration. Regular
rotary table calibration involves the use of a rotary encoder, sine plate and level. These
tools, however, are prone to error when compared to upgraded options. Because a
rotary table is double­checked with a sine plate, it must be physically moved each time.
Set­up time is lengthy, and sine plates are expensive for their large margin of error.
Modern rotary motion calibration often uses Doppler calibration and laser interferometer
systems. These systems offer multi­optical support, an indexing table and high
accuracy.
Modern Calibration Tools
While the above calibration tools are useful, their limitations are only growing. The
industry is evolving, and optimized processes require pinpoint calibration accuracy.
Such a need for higher machine accuracy has increased calibration system demand,
pushing the development of precise, versatile options. The upcoming generation of
calibration tool equipment consists of two high­powered, laser­based measuring

10. systems: The Michelson interferometer and the Laser Doppler Calibration System.
Examine them below. If you can, prioritize them when considering your workplace’s
calibration equipment.
Using the Michelson Interferometer
Today’s Michelson interferometers utilize technology invented in the 1880s. Using a
white light source, the interferometer harnesses a movable mirror and fixed mirror to
precisely measure angles and position. Today’s interferometers use helium­neon lasers
and two corner cubes, however, as they’re far more accurate.
Single­Frequency Beams
The first of two types of Michelson interferometers uses a single­frequency helium­neon
laser beam and a beam splitter. When the beam passes through one of the machine’s
moving corner cubes, its other half is reflected into the other cube. These reflected
beams return, meeting one another within the beam splitter. These beams, together, will
create an interference fringe pattern. Once counted by a photodetector, the fringes
reveal a cycle of change intensity.
Two­Frequency Beams
The Michelson interferometer is available in a two­frequency variant. The two­frequency
interferometer, unlike the single­frequency interferometer, circumnavigates the regular
electrical noise, gain drift and slight inaccuracies of the single­beam variant. It uses two
helium­neon laser beams of different frequencies, creating an overall carrier frequency.

11. Distance information, then, is carried within AC waveforms—not a one­frequency
device’s DC wavelengths. A two­frequency interferometer is a fantastic calibration
device, but it requires the installation of permanent magnets and high­quality optical
components to ensure accurate measurements and polarization. Scattered light,
otherwise, may be lost when returning to the machine’s laser resonator.
Using the Laser Doppler Calibration System
The Laser Doppler Calibration System requires the use of a laser Doppler displacement
meter, abbreviated as LDDM. The LDDM utilizes optical heterodyne techniques,
electro­optics and several phase demodulators to measure a movable corner cube’s
position. This measurement, when compared to a machine’s operations, can expertly
track angles—calibrating it.
LDDM systems don’t suffer from issues with stray light and polarization. They
additionally don’t require specialized optics to maintain operations. Windows, inserted
into an LDDM system’s beam path, alongside several basic mirrors, can reflect the
system’s laser back. A compact system, the LDDM can be mounted easily. For this
reason, it’s a highly versatile machine tool that eliminates the need for multiple machine
components.
A Doppler system requires two optics: a retroreflector and a laser head. A laser
interferometer, meanwhile, requires three separate optics to be mounted via tripod
beyond the machine tool. In many cases, the Doppler system is far easier to install, set
up and operate. Data collection is automatic, which aids immediate measurements.

12. Future Calibration Tools
The world of CNC calibration is constantly changing. In the near future, machine tools
will likely feature immediately accessible calibration systems. These systems will be
formatted into a machine’s software, giving users immediate access to custom
solutions. Capable of automatically correcting errors with measurements, these
calibration tools will additionally collect and chart information automatically, helping
users determine a machine’s tool condition quickly, effectively and reliably.
Fortunately, cost­effective and efficient calibration systems exist today. While the
industry awaits on­line calibration options, quick­checks and predictive maintenance are
still highly efficient. With regular discipline, a broad PDM program and the correct tools,
in­house specialists can significantly reduce machine downtime, increase investment
returns and keep organizational operations at a peak.