PC-DMIS Tech Tip: A beginner's video guide on why an alignment is done in CMM programming and a demonstration of a Basic 3-2-1 Alignment in PC-DMIS.
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Welcome to another video on Tech Tips from CMMXYZ. Today, let's discuss about a basic 3-2-1 Alignment, and why an alignment is done. Before we start aligning the part, let's understand why should we align the part to the CMM? When an object moves in free space, it has 6 degrees of freedom. Three translational and three rotational. Initially, when the part is placed on the CMM, the part is equivalent to an object moving in free space. In this case, it's inside the volume of the CMM.
When the machine is homed, CMM establishes a machine startup access. At this point, CMM has no idea where the part is in the machine volume. This means the part is moving inside the volume of the machine with 6 degrees of freedom. In order to make the machine understand where the part is, we have to restrict all 6 degrees of motion by aligning it to the part. This will shift the coordinate system from the machine home position to the part.
Now, let's create features for the alignment. We have different ways to create features, but I'll be using measured features in this video. Keeping the CMM in manual mode, and screen in program mode, let's go ahead and create a plane. Let's take three points on Datum A to create a plane. Press End to create the feature. Now, let's take two points on Datum_B to create a line and a point on Datum_C.
Let's create an alignment using these features. Before we do that, let's change the names of our features. Let's change plane to Datum_A, line to Datum_B, and point to Datum_C. To open the alignment dialog box, you can go to Insert, Alignment, New, or you can press CTRL+ALT+A.
In the Alignment Utility box, we can see three features Datum_A, Datum_B, and Datum_C, which can be used for the alignment. When the part is not aligned in the graphic display window, you can observe that the trihedron moving indicating 6 degrees of freedom.
In the alignment dialog box, let's select the plane, which is Datum_A, and level it to ZPLUS. We are leveling it to ZPLUS because the vector of Datum_A is facing towards ZPLUS of the CAD-axis. Leveling it to Z-plus stops the rotation in Y-axis and in X-axis. After we level the Datum_A plane in ZPLUS, two rotations have been restricted, one in X-axis and one in Y-axis. There are three translations and one rotation remaining.
To stop the rotation in Z-axis, let's select the line Datum_B. As you can see in the graphic display window, the line is pointing towards X-plus direction of the CAD-axis. Let's rotate to X-Plus about ZPLUS. Now, there are three translations. Let's stop the translation in Z-axis by selecting Datum_A plane and click on Origin. Then let's select line Datum_B to stop the translation in Y-axis, and Datum_C to stop the translation in X-axis.
Now, the trihedron has stopped moving, indicating the restriction of all 6 degrees of freedom. Let's click Okay to complete the alignment. This was a video on basic 3-2-1 Alignment. Thank you for watching the video.
