Today Coordinate Measuring Machines are offered by a number of manufacturers in all kind of sizes and uncertainties. In order to choose the most suitable 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 probe extension. As the example below shows, some parts require a coordinate measuring machine with a much bigger measuring range than the actual part dimensions.
Example:
Minimum required measuring range in X: 1610mm
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: Calculation of the required E-specification for given distances and diameter
Coordinate Measuring Machine A
Coordinate Measuring Machine B
E = 0.6 + L / 600
E = 2.2 + L / 400
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
+/- 0.0029
29%
1:3.4
2
1
Distance
320
0.012
-0.012
+/- 0.0011
9%
1:10.6
+/- 0.0030
25%
1:4.0
3
1
Distance
22
0.000
-0.008
+/- 0.0006
16%
1:6.3
+/- 0.0023
56%
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 Coordinate Measuring Machine can be selected.
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.