How to select a 3D Coordinate Measuring Machine


Today Coordinate Measuring Machines are offered by a number of manufacturers in all kind of sizes and with all kind of measuring errors. In order to choose the most suitable 3D measuring machine for your individual requirements, we recommend to follow 2 basic steps:

Step 1: Determine the required measuring range of the CMM

To be considered: The dimension of the biggest part, the fixture, the diameter of the probe head as well as the length of the longest stylus.
As the example below shows, some parts require a 3D coordinate measuring machine with a much bigger measuring range than the actual part dimensions.

Example:

How to select a CMM coordinate measuring machine - measuring range
Minimum required measuring range in X: 1660mm



Step 2: Determine the maximum permissible CMM errors E, P and THP

All features to be inspected (Distance, Diameter, Form and True Position) are compiled in a chart, together with their tolerances. Then the CMM specifications E, P and THP (according ISO 10 360), which still ensure a sensible ratio of "Tolerance to CMM error", can be calculated.

Example: Comparing the "E" spec of 2 Coordinate Measuring Machines for given distance and tolerances.


  Coordinate Measuring Machine A Coordinate Measuring Machine B
E = 0.6 + L / 600 E = 2.2 + L / 300
No. Sheet Feature Nom
[mm]		 U-Tol
[mm]		 L-Tol
[mm]		 CMM Error
[mm]		 In % of
tolerance		 Ratio CMM Error
[mm]		 In % of
tolerance		 Ratio
1 1 Diameter 286 -0.020 -0.040 +/- 0.0011 11 % 1:9.3 +/- 0.0032 32 % 1:3.2
2 1 Diameter 320 0.012 -0.012 +/- 0.0011 9 % 1:10.6 +/- 0.0033 27 % 1:3.7
3 1 Diameter 22 0.000 -0.008 +/- 0.0006 16 % 1:6.3 +/- 0.0023 57 % 1:1.8

Based on the maximum permissible CMM errors E, P and THP, calculated in above chart, and with the minimum measuring range determined in step 1, the most suitable 3D Coordinate Measuring Machine can be found.

Hexagon Metrology GmbH offers a free, unbiased analysis of the minimum required measuring range as well as the maximum permissible CMM errors, based on your part drawings.

All you have to do: Send your drawings or your CAD file to your local representative, listed under contact.