​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