HOW TO MAKE POSITIONAL DEVIATION AND REVERSAL ERROR CHECKS
TECTIP No. 018

   
SUBJECT:    Machine Geometry       
APPROVAL:    Ken Baeszler
PREPARED BY:    Mark Barrier
SYSTEM TYPE:    EDM

   
OBSERVATIONS:   
Many companies require that a machine tool be certified periodically to assure accuracy. By taking the following actions, you can check for positional and reversal errors on your systems:
           

• For our example, we will assume you are inspecting the Y-axis.
• See Figure 1 for pictorial details of the measurement setup.

 
ACTIONS:   
Perform positional deviation and reversal error checks for the Y-axis.

• Gently place a straightedge on the table parallel to the X-axis.  Attach an indicator (0.0001” graduation or better) to the quill and apply it to the face of the straightedge.  Align the straightedge parallel to the X-axis travel.  Gently strap the straightedge in place. Move the X-axis to midstroke when complete.
• Make a –1.0000” movement in the Y-axis direction.  Slide a 1.0000” gauge block between the indicator and the face of  the straightedge.  Zero the indicator.  Slide the gauge block in and out several times in order to verify a repeatable zero point.
• Make another –1.0000” movement in the Y-axis direction.  Slide a 2.0000” gauge block between the indicator and face of the straightedge.  Read the error displayed on the indicator.  This value indicates the positional deviation for a 1.0000” increment of movement.  Make a +1.0000” movement in the Y-axis direction.  Slide a 1.0000” gauge block between the indicator and the face of the straightedge.  Read the error displayed on the indicator.  This value indicates the reversal error for this movement.

Note:    The accuracy of this measurement is directly dependent on the accuracy of the indicator and gauge blocks being used.