The first step in creating an alignment is to know the proper methodology of creating a program. Keep in mind that the method that will be explained today is not all encompassing. There are many ways to approach alignments. This is one of the ways that has been successful for me. I use this approach in all my programs.

A sound program should have at least two alignments; 

•  A manual alignment 

•  A Direct Computer Control (DCC) alignment 

 

The manual alignment tells the CMM where the part is set up and the DCC portion of the alignment then refines that placement by measuring the datums while under computer control. It is best to have the computer take control and measure the datums for alignment rather than the programmer because the programmer can introduce variation into the measurement process that a computer won’t. 

The manual alignment in this example would use a plane (PLN1) to control the Z axis height and to level the part (3 degrees of freedom constrained). 

 

The alignment would use two lines (LIN1 and LIN2), created from two points each along the sides to constrain the X and Y axis by creating a constructed point using LIN1 and LIN2 to create PNT5 (2 degrees of freedom constrained). The alignment would use the line (LIN1) created along the X axis to control the rotation, or “clocking”, of the part (1 degree of freedom constrained). Please note that the proper workplane needs to be recalled or the lines that are constructed will be incorrect.

 

Once the manual alignment has been completed a DCC alignment can be created. The same type of geometric features would be used to create the DCC alignment.  Once the DCC alignment is completed then measurement of the itemized (or ballooned/numbered) blueprint can begin. Keep in mind that for each set of features that need to be reported from a different alignment than what was measured above another alignment should be created prior to the measurements of those features. This is good measurement practice.

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