Measuring the Accuracy of Machine Tool Rotary Table

A rotary table is a machine tool accessory with a rotatable table surface for clamping workpieces and achieving rotary and indexing positioning, also known as the fourth axis of the machine.

The working accuracy of a rotary table involves three aspects: positioning accuracy, repetitive indexing accuracy and origin-return accuracy.

The question of how to check the accuracy size is important.

I. Rotary table positioning accuracy detection

For positioning accuracy measurement, a standard rotary table, angular polyhedron, angle encoder and collimator are required.

The measurement method is to turn the table to an angle, both forward and reverse, then stop, lock and position, and it uses this position as a reference with rapid rotation in the same direction, locks positioning and measurement every 30 seconds.

It is required to measure one week in each direction of forwarding and reverse rotation, and to position 7 times in each direction.

It should take the maximum value of the difference between the actual corner and the theoretical value of the measured positioning position as the indexing error.

If the measurement is of a CNC rotary table, the average position deviation and the standard deviation should be calculated using the method specified in “Evaluation Method of Position Accuracy of Digitally Controlled Machine Tools”.

The sum of the maximum value of all average position deviations and standard deviations, minus the sum of the minimum value of all average position deviations and standard deviations, the result is the positioning accuracy error of the CNC rotary table.

Considering the actual use requirements of the dry-type transformer, it should generally be focused on the measurement of 0 degrees, 90 degrees, 180 degrees, 270 degrees of these right-angle equipoints, requiring that the accuracy of these points should be one grade higher than other angular positions.

It should be noted that the existing fast positioning accuracy measurement method for some machines, when using different feed speeds for positioning, it will get different positioning accuracy values.

In addition to this, the measurement results are dependent on the ambient temperature and the operating condition of the axis.

II. repeatability indexing accuracy test of the rotary table

For the measurement of repetitive indexing accuracy in the rotary table within a week, arbitrarily selected three positions for three times repeated positioning, respectively in the positive and negative direction of rotation for detection.

The detected value is subtracted from the corresponding position theoretical value, the largest difference for indexing accuracy is taken.

If the measurement is CNC rotary table, it should not arbitrarily take 3 positions, but take a point every 30 as a measurement of the target position, from the positive and negative direction of each 5 times fast positioning.

The difference between the actually reached position and the target position is the position deviation of the rotary table.

Finally, the standard deviation is calculated in accordance with the calculation method “digital control machine tool position accuracy assessment method”.

It should take the value of the largest of the standard deviations at each measurement point then multiply this value by 6 to get the repeatability of the indexing accuracy of the CNC rotary table.

III.  origin return accuracy test of the rotary table.

The repeated positioning accuracy of each coordinate axis is the most basic accuracy index reflecting the axis, , it reflects the stability of the axis motion accuracy, which can not be assumed that poor precision machine tools can be used for production stability.

For the detection of the return-to-origin accuracy, the return-to-origin should be performed once at each of the 7 arbitrary positions, and the maximum difference obtained by measuring the stop position is the return-to-origin accuracy.

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