All machining centres are advertised as “High Precision Machining Centres”, so how do you make comparisons between each machine? It is important for you, the customer to achieve the results you require and it is with this in mind that KERN do not promote their machines by highlighting the positional accuracy of the machine but rather what can be achieved “on the workpiece” which is what you want.
Accuracy on the workpiece also includes spindle concentricity another important factor to consider. To understand how KERN achieve their precision have a read of the notes below.
The smallest programmable increment is 0.0001 mm (0.1 µm) and the axis positioning is via a closed loop feed-back from linear glass scales with a low pressure air purge to ensure absolute cleanliness.
KERN, being a German machine tool manufacturer, use VDI/DGQ3441 as a standard for the measurement of accuracy on their range of machining centres. Positional accuracy is ±0.0003 mm. View the axis measurement certificate for an X axis movement. It is important to understand the
differences between German VDI and Japanese JIS national standards when comparing data. A good example is the data for Umax the maximum reversal error for hitting a certain point by approaching that point from both directions of movement.
Additionally KERN use the Heidenhain KGM measurement system to check both the positional accuracy and circular interpolation of movement.
Also shown is a test result sheet for circular interpolation movement, again you will note reversal error results show a slight difference (circular interpolation moving clockwise to circular interpolation moving counter-clockwise). It would be very nice to say we can machine a circle by circular interpolation better than 0.001 mm and this is possible using a slow feedrate. However KERN are a company that bases its test results on practical applications and in the test results shown are using a feedrate of 500 mm/minute and therefore expect a deviation greater than 0.001 mm. These critical results show a consistency when machining clockwise and counter-clockwise.
To machine parts accurately another critical feature is the spindle run-out. In the test report sheet it shows run-out to be 0.002 mm at a distance of 100 mm from the spindle nose, thus ensuring your endmills and drills have the highest possibility to achieve your tight tolerances. This feature is even more
important when “micro machining” and using small diameter endmills and drills. The cutting tools do not break because they are small, but because of spindle runout applying extra forces in a radial direction.