When most people of what makes a CMM affordable the first
impression is initial purchase price, while this is an important part of the purchasing decision
there are many other costs that go into making an informed decision. Items such as training
costs, software support and contracts, calibration costs, service rights, ease of use and ease of
repair. While these may appear to be insignificant let’s see how they may add up over time
Training costs, while typically not anticipated there is continual turnover of employees with
desired skills. Most CMM manufacturers have set charges for training classes and depending
on the software may have requirements for both basic and advanced classes to insure the
effective use of the CMM. Typical basic class costs around $2,500.00 and an advanced class
around $3,500.00, plus the cost of expenses as you send your student to the manufacturer
which will add another $500.00 to each training class
Software support and updates are free for the first year from most manufacturers, after the
first year, the cost is optional, but if you require support they will not help until a contract is in
place and if you need to upgrade (such as a change in the windows platform you are running) as
a rule they charge for every missed contract from after the first year. So, over the period of 5
years you can expect to spend an additional $10,000.00 at minimum laser the costs can go up
significantly
Service rights, most CMM service requires a key or password to get into the diagnostic software
and calibration files, this means that you are typically required to go back to the manufacturer
for any support issues. Open technology platforms offer by a few companies can give you
access to other support sources and do not hold you captive to the OEM, so the supplier must
provide you with a high level of service or you can go elsewhere for support not so with most
manufacturers, you become the owner of your machine not the OEM when you use open
technology
Ease of use, should be a primary consideration in the purchase of any CMM. The more difficult
the software is to use, the less use you receive from the product. Jobs will be sent to other
means of inspection, if the programming time on the CMM is lengthy or drawn out, the loss of
an operator due to illness or vacation can cause down time as no fully efficient replacement is
readily available to fill the spot. The requirement on many CMMs to have to create a part
program in order to effectively measure a part creates additional delays for one off inspections,
when the machine can not be used effectively to measure off a drawing or do simple
inspections
Ease of service, a number of OEMs use proprietary products in the CMM, things like a simple
probe head if you are using a Renishaw based system can be swapped out by the operator and
are typically available over night on an exchange basis, with proprietary products you usually
have to wait not only for the probe but also a service technician to properly install the
equipment, this can entail multiple days of unanticipated down time

So depending on the CMM over a period of 5 year your initial investment can cost more than an
additional 30K even if every thing runs without error and if there are no problems, so being
aware of these costs you should consider systems with
Free software updates and support for life
Non-proprietary packages of any type hardware or calibration
Open Technology
Ease of use in the software with lower training costs
What does a calibration cost?
In many cases the initial purchase price is just the beginning in having an affordable CMM

When looking for a piece of measuring equipment there are a few basic items that every potential user needs to understand during his research if not prior to, so you can make a good decision, some of these are accuracy, measurement range, who and how you will use the equipment the most, whether you are looking to do prismatic part inspection or non-prismatic part inspection, whether you wants to gather form data and how detailed they wants this information, and what quantity you will be doing his inspections in, will most of your work will be one off, if you will be doing small batches or if you will be doing productions runs
First let’s talk about the key item on everyone’s list, and that is accuracy.  First is understand what your part tolerance is, typically you want something that is at least twice the accuracy that you intend to measure for a DCC machine and three times the accuracy for a manual system, due to increased operator influence on the measurement.  IE: if your tolerance is 0.001 you need a machine that is at least 0.0005.  Accuracy is typically given in a formula so do the math and work out the formula, also insure that the accuracy stated against a standard such as ISO 10360, and also insure that the accuracy statement is at least 2 sigma to insure reliable results
Determining machine size sometimes is sometimes difficult, because measurement range and part size are not always true correlation. Features can create a need for extended machine sizes.  An feature such as a cylinder perpendicular to a plane with some depth can create a need for a longer axis.  IE 14-inch-long part with a 8 inch deep cylinder could generate the need for machine with a minimum 22 inch measuring length in order to meet the requirement for measuring that feature.  Supplying part prints to a potential supplier and have them quote to your need is always recommended, but the quote should be explained in detail for each item included with the reason why either in writing or in a meeting.
How you plan on using the machine the most is important as this will help determine, things to be considered are number of parts that will be inspected, will it be small lots, one off parts or quantity inspection.   If you are measuring small lots or one off parts software simplicity should be high priority, it might be important to have software that would allow you to bring a part to the machine and start measuring immediately without having to create a program, it should also have the ability to store this program for future use.  It would also be ideal that the same software would allow you to program from a CAD file if needed.   IF the software does not offer this type of flexibility or it is difficult or clumsy to use and not intuitive, you might rule this out as a possibility, but if you are running large runs of the same parts, then the capability to program off line and create programs from CAD may be more important even if it is more difficult to use.
Other considerations that are to be looked at should include, what are the parts like, are they basic prismatic measurements, such as blocks, cases and others or do we do free form surfaces or non-prismatic parts, such as airfoils, blades etc. do I want to do form type measurements, will I be trying to reverse engineer items, each of these need to be reviewed as they can affect the price that you will pay, by increasing the complexity of the software, creating a demand for specialized or dedicated probe systems.  Will I need to measure flexible parts such as gaskets, rubber or plastics that are thin walled and can create reproducibility issues.  Most of all be prioritize what you must have and what you would like to have and set a budget that you can live within. 

The initial purchase price for a CMM is just the beginning of the investment, there are many costs that come with CMM ownership that goes beyond the price that you pay on the purchase order.   
The first one that most owners run into are the expenses that go with the training provided with the CMM.  While almost all CMMs come with some kind of training included, this training is typically offsite at the OEMs facility. If you are lucky enough to be within driving distance of a facility the cost is minimized, but if not, you face Travel expenses that are at minimum hotel costs, meals, and transportation.  There is also overtime that may be involved due to the distance traveled by the employee.  This is then compounded by the fact that the efficiency of your employees after they come out of training (learning curve) is compounded by the fact that the training is done on standardized parts and the must learn to apply theory of the training to your actual parts.  Onsite training is much more effective provided the trainer will work with your parts and applications in teaching
The next cost that lies hidden is the software maintenance and support, most OEMs provide only one year of support and upgrades with the product, after that year is up, they will insist in the purchase of a software contract which can be as little a $1,000.00 per year to get this turned back on, but depending on options and software configurations can run more than $6,000.00 per year
Another hidden cost deals with those company that use proprietary products in critical components of their machines. If the OEM uses Renishaw products such as the PH10 these can typically be obtained over night and can be exchanged by the CMM operator with minimal or no support, the cost is typically less that $5,000.00.  If you deal with a proprietary product, you not only have to pay the exchange rate for the probe from the OEM, ($6,000.00 or more is typical) you then have to wait for a service technician to be available to install that part that can be over a week, depending on your location, thus not only paying in excess of $8000.00 to $10,000.00 for the service call but also the hidden cost of machine down time which can limit your ability to ship products to your customers
Another cost is calibration, a typical calibration from an OEM is in excess of $2,000.00 and they control the compensation software that precludes you from using other sources that could be half the price or less, so if possible, you should look for systems with an open compensation map.   Another cost of calibration is frequency, typical OEM will recommend an annual calibration, while it is your quality systems that should set the calibration interval cycle based on your actual use of the system.
Service Rates are another cost while they may seam simple based on hourly rates you need to look at hidden charges for things such as equipment rentals, (which are required to do the job but not part of the base price), charges for processing travel expenses, minimum daily charges, premiums on travel costs. That are hidden within the service rate sheets
Training costs and ease of software use are other charges that you will eventually incur, while none of us like to lose employees this will eventually happen and training cost should be part of your ownership calculation.   Most software’s typically require two stages of training to be effective basic and advanced at $1,500.00 to $5,000.00 per person per class this can add up to a rather large investment, the similar the software the easier to use the lower the cost of training.
All of these costs are directly tied to the initial purchase of the CMM and should be considered in the purchase of the machine you will buy

​

​In today’s market CMM accuracy is usually stated as ISO10360-2.  This is the statement of volumetric accuracy that is given dependent on the distance of the measurement you are making.    The statement is usually done in a simple formula such as accuracy equals X.X + L/XXX. 
The first part of the formula is a constant and should be considered in every measurement taken regardless of the distance traveled.  The following are a couple of examples
Part Length is 500 mm, machine accuracy is stated as 2.4 + L/250
Substitute in the distance being measured in place of the L
2.4 + 500/250
 2.4 + 2
 4.4 microns
0.00018 inches approximately
Part Length is 1000 mm
2.4 + 1000/250
2.4 + 4
6.4 microns
0.00028 inches approximately
 
Some companies state the accuracy formula differently in the second term to make the accuracy seam better an example would be 2.4 + 4L/750.  The formula would work out as follows
2.4 + 4L/750
2.4 + 4*500/750
2.4 + 2000/750
2.4 + 2.67
5.07 microns
0.00022 inches approximately
 
If you look at the two ways of presenting the accuracy 2.4 L/250 may not look as accurate at first glance as 2.4 + 4L/750, but if you work out the formula it shows that this is not true
Just an additional note some companies, will calibrate a machine quoted to ISO to the old B89 standard, there is a significant difference in the measurement testing.  ISO requires you use certified length devises such as Step Gage or Gage Block, B89 uses a ball bar that is of one uniform length.  Additionally, by measuring spheres instead of steps you average the probing error with the ball bar.  If the machine is sold to ISO you should insist that it calibrated to the ISO standard to ensure that it meets the requirements
 
There are other parts of the standard that we are willing to discuss such as ISO 10360-4 and 10360-5 please contact sales@mastersprecision.com

​Understanding temperature and it its effect on CMM measurement can be very confusing to most people.  There are many things to consider when deciding how this effects your measurement.  How does it affect the part, how does it affect the machine?
There are some major components to temperature,
Ambient Temperature
Rate of change
Drafts or localized effects
 
Ambient Temperature is the general room temperature that the machine is occupying.  The CMM manufacturer will specify and ambient and with a nominal deviation A typical statement would be 68 degrees F plus or minus 2 degrees, some machines will allow a larger spread such as +/- 4 degrees or tighter spread such as +/- 1 degree.  The Key in this statement is the spread not really the nominal.  For instance, if the machine is calibrated at 70 degrees in the +/- 2degree spread you can expect it to measure parts effectively from 68 to 72 degrees F, you might incur issues if you were to run the machine at 66 degrees
 
Rate of change is important as rapid changes in temperature even when within the specification can cause an issue.   If your temperature is changing quickly over a short period the machine will be moving during the periods of change and more importantly the part you are measuring due to is smaller mass or different material will be moving at a faster rate due to its reduced mass
 
Drafts are another cause measurement issues, because they can cause localized cold or hot spots on the CMM or part, deforming the part or machine until it stabilizes
 
Localized affect that can exist is divergent temperature between the manufacturing and the quality environments.   An example of this would be taking, a part sample from the manufacturing area to the quality room and measuring it immediately.  If the manufacturing area is 2 degrees warmer then the QA area on a 10-inch steel part this could be an error of 0.00018 in the measurement and on a tight tolerance part this could consume a large portion of your manufacturing tolerance
(calculation based on a general specification for thermal coefficient of expansion for steel)
 
There are many other effects such as gradient temperature, humidity and others that can cause issues to measurement values, these are some of the most common ones that are over looked when using a CMM or other measurement device.  If further information is required please contact Masters Precision at sales@mastersprecision.com  

Probe Tip Lengths effect measurement in in 2 primary ways

First is probe bending.   Probe tips vary in stiffness depending on the material, it is always better to keep probe tip as short as possible, typically lighter weight probe tips are not as stiff as heavier probe tips

Example going from a from a 60mm stylus to a 250mm probe tips on a CMM with an accuracy of .5 + L/1000 has shown a change in measurement accuracy of 2 micron, while this is small it could have an effect on tight tolerances measurements that require longer probe tips

Second longer probe tips magnify machine errors, errors such a straightness, pitch, twist or yaw, can be significantly magnified by the probe length. 

An example would be the manufacturer states that a 60mm probe is used for proving machine calibration results.   If you have a feature that requires the use of a 240 mm long probe tip, you could see the amplification of the error of the machine error 4 times greater than the results shown in the machine calibration

​If you are looking into purchasing a CMM it is recommended that you define your tightest tolerance measurement and insure that the machine has the accuracy capable of performing to this requirement, if that measurement requires a longer stylus you may want to have a demo on the part to see the results, it is even better if you right a performance specification into your purchase spec for the CMM

​Scanning is a term that is widely used with CMMs to mean three different types of

measurement. Each type of measurement has both positive and negative effects on the

measurement process these three basic types are.

Digital or peck scanning: Which is taking individual points in close proximity along a line or a

cross a surface or other geometric feature to define the feature. Spacing of the points are

determined by the operator/programmer dependent on the feature being measured, It is

inexpensive and does typically not require additional hardware with the CMM and is good for

simpler applications or those features that do not require a lot of definition. It is not a good way

to do form measurement if tight tolerances are required or if there are rapid changes in the

surface or form to be measured

Analog scanning or continuous contact scanning: Is the process where a stylus is in

continuous contact with the surface of the item to be measured, this provides greater accuracy

typically and allows for more data points. Faster than digital scanning in most cases and

provides greater point density. Programmers need a higher level of skill as they must consider

and apply filters to the points gathered to eliminate errors, such as outliers and friction issues

that come from the styli being in constant contact with the surface. A great number of

improvements in this technology has come forward in the past few years with

a) accuracy dependent on system speed. (the faster you move the greater the error) which

is another consideration for the operator when writing the program.

b) Revo 5 axis technology which allows scanning at up to 500mm per second and 400 data

points a second without degradation of accuracy and that with its improved technology

reduces and in some cases, or eliminates the need for applying filters to the scanned

This type of scanning is more expensive than digital scanning, but gives greater accuracy and

can provide throughput improvements on some parts up to 90%

Non-contact or Laser scanning: Is the third type of scanning being used in the market today,

it is extremely quick and gather millions of data points in seconds. This type of scanning is

great for applications with greater tolerances, (such as castings, plastics or rough machining

operations) or flexible parts where contact can deform the part and thus the measurement or

reverse engineering applications. Things that might be of issue are, parts with high reflectivity,

parts that are clear or opaque that do not reflect light well, part tolerances, (laser scanners

typically have a greater than 10-micron error in practical applications) Operator skill level

required to handle the set up and filtering of the part data, and that the device is line of site, so

that some features may not be able to be measured effectively and require additional

measurement with a contact type probe

These are rudimentary explanations of scanning with a CMM and are intended only to give a

basic understanding, if further information is needed please contact Masters Precision via email

sales@mastersprecision.com

Masters Precision is pleased to announce the Aberlink educational product offering to Schools and Universities.   This model of CMM is the Axiom series, but with the rebranding of the name to Educate.  This offering is exclusive to educational institutions and includes the following

• Rebranded Axiom CMM Model of their choice and configuration with Mark IV Software
• 10% discount on the machine and accessories
• Free CAD Programing and CAD compare modules with the CMM
• Offline Software seats at $95.00 per copy