PCS Example #5

Plane - Cylinder - Circle

In this exercise, we will create a part coordinate system utilizing a plane for the orient and origin, a cylinder for the alignment followed by a circle for the last components of the origin. The following example assumes the part is placed on your CMM where the cylinder of the GeoWidget is pointing in the -X direction.

figure 1, Datum target layout	figure 2, Complete PCS

Step 1

Request a -Z plane <b>, if auto-direction is not activated, you will be prompted for the probing direction which you should select as -Z. You will then be prompted to "Measure -Z Plane", (if auto-direction is active "Measure Auto-Dir Plane"). Capture points A-1, A-2, A-3 and A-4 as shown in figure 1.

Step 2

Select Orient <j>. The orient command will create the primary datum on the axis that is most normal to the machine coordinate system. In your PCS Setup Guide, the Z Axis will be signed off.

Step 3

Select Origin <l>. This will establish the Z origin which is determined by the normal direction of the -Z plane.

Step 4

Select Cylinder <c>, if auto-direction is not activated, you will be prompted for the cylinder type, ID OD IR OR, choose OD. Capture the six data points identified as B-OD/6, see figure 1.

Step 5

figure 3, Select Axis

Select Align <k>. A cylinder offers the possibility of more than one alignment solution. In our example, you have solved the Z axis orient by utilizing the previous plane, therefore you are attempting to align the remaining axis, or XY. Select the XY button from the Select Axis dialog, see figure 3.

Your ICS will now update to include the secondary datum which is derived from the longitudinal axis of the cylinder. In this example, the cylinder was reported as piercing the YZ ICS base plane, therefore the normal to that plane is X with a direction of -X. The PCS Setup Guide will update to reflect the XY Axis have been solved.

Step 6

Select Circle, if auto-direction is not activated, you will be prompted for the Circle type, ID OD IR OR, choose ID. Capture the four data points identified as C-ID/4, see figure 1.

Step 7

Select Origin. the Circle, which is 2D, provide two directions when establishing an origin. In our example, the circle can be used for the X and/or the Y direction. The origin command will prompt you whether to use the X and then the Y. For our example you should answer Yes to both requests. Upon completion, you will have established PCS 1, see figure 2

There are times when you are required to utilize more than one 3D feature to solve for the part coordinate system. In this example we used a 3D feature, a cylinder, from which the alignment is derived, therefore you are prompted to solve which part coordinate system component to solve.

figure 4, Final Inspection Report

From this example you should note that the data point spread on the cylinder is approximately 1.25"in the X axis and the width of the part is 4.50". This can be a cause of concern as it is poor inspection practice to have your data point spread ratio to the width of the part less than 50%, in this case only 28%. The possibility of skewing your part coordinate system increases dramatically as your ratio is reduced.

However, conditions do arise that do not allow for proper setup and as the inspector, you are challenged to determine the best data point spreads with the features available that will produce a sound part coordinate system.

Related Procedures:

Download PCS Example #5 (.zip)
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Orient, Align, Origin, Plane, Cylinder, Circle