Align

Coordinate System Secondary Datum

k	PCS→Align
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Align acts on the last measured or recalled 3D or 2D directed feature or pair of non-directed features which could serve to create a 2D or a 3D directed feature. For example, a pair of 1D co-directional points, pairs of coplanar 2D points, or pairs of 3D points. The Align command will see through transparent operations such as other PCS formation commands, distance, angle commands, etc. Align establishes the directions of the secondary and tertiary PCS axes, with the selection of X, Y and Z determined by the MCS X, Y or Z axis to which the directed feature axis is most parallel. Geomet will validate the last feature(s) to determine whether they are capable of providing a secondary datum, see table 1.

figure 1, Select PCS Base Plane for Alignment

Align, when executed in an ICS directly after the orient has been established, makes an automatic choice of the alignment axis. For example, if the orient command resulted in establishing the Z axis, then the Align command will rotate about the Z to establish the secondary datum.

When the Align command is executed in an established PCS, the resulting operation creates a new PCS by aligning to the requested feature. The Align command will determine the alignment axis when a pair of co-directional 1D points or coplanar 2D features are used. When using a pair of 3D features or a 3D axial feature, Geomet will prompt for the PCS base plane to align in, see figure 1.

	1D Point	2D Point	3D Point	Circle	Ellipse	Line	Plane	Sphere	Cylinder	Cone*
Align					X,2	X,1	X		1	1
Notes: 1 - 3D Lines, Cylinders, Cones the axis is projected into a specified PCS base plane, then aligned. 2 - Utilizes the Major or Minor Axis of the Ellipse.
table 1, Align based on a single feature

 

	1D Point	2D Point	3D Point	Circle	Ellipse	Line	Plane	Sphere	Cylinder	Cone
1D Point	X	X	X	X				X	1	1
2D Point	X	X	X	X	X			X	1	1
3D Point	X	X	X	X	X			X	1	1
Circle		X	X	X	X			X	1	1
Ellipse		X	X	X	X			X	1	1
Line
Plane
Sphere	X	X	X	X	X			X	1	1
Cylinder	X	X	X	X	X			X	1	1
Cone	X	X	X	X	X			X	1	1
NOTES: 1 - Based on projected 2D Pierce Point, not the axis. 2 - Oval Slot / Slot Web / 4 Point Intersect are treated similar to a 2D Point
table 2, Align using 2 feature combinations

Special Considerations

Care should be observed to select a feature that provides a well defined alignment. The feature should be sufficient in length to prevent adding errors into the final results. For example if a line is used that is 1"00 in length and the inspected part is 10"00 in overall length, then we would have a 1:10 ratio. If the misalignment of the feature to part was 0.0001", then at 10"00 it would be 0.001" in errors, see Technical Note #2 for some common errors in a CMM.

Using 3D features, such as a Cylinder should be used with care. Using the Cylinder as an example, let's first review how a Cylinder is projected into the current PCS Base Planes.

figure 2, Cylinder Projection

In figure 2, the Cylinder is shown piercing the XY base plane of the PCS. If the orientation plane was also the XY base plane, then any alignment would take place along the angle AX/Y. The length of AX/Y is the protection of the end points of the Cylinder Axis into the base plane XY. If the Cylinder axis was parallel to the normal vector of the orient vector (plane vector) then the length between the projected endpoints would be 0.00"! and no alignment would be allowed.

In figure 2, the cylinder could be used as an alignment feature only if the Orient feature was the YZ or ZX plane.