CAPPS/LOCKPART is used to align two coordinate systems' origins (Part Coordinate System[PCS] and Machine Coordinate System [MCS]) when using CAD or nominal data.
When a new CAD model imported into Capps, its PCS is automatically aligned to MCS since that is the only know location in a machine volume.This is usually not the case with the physical part which is located somewhere else in the machine volume. Therefore, an alignment is required to teach where the PCS is located relative to MCS location.
In the below example, a CAD model for AAT Block is imported into Capps and its PCS origin is shown:
No matter what alignment method is used, the main purpose is to measure some actual features and use them to create same coordinate system with the correct origin, as defined on the CAD model. As the user starts measuring features, they will appear somewhere in the space on Capps Graphics Window, not on the CAD model, since there is no active alignment yet.
In this case, a plane, two lines are measured and an intersection point is constructed by intersecting two lines to create the alignment, that will allow us to create PCS and origin for the physical part that is on the machine.
Using Alignments Menu - Setup dialog, a plane (PL1) that is measured on the top surface of the part, is used to control translation about Z, rotation about X and rotation about Y, to set Z origin as shown below.
A line, (in this case LN2) is used to control translation about X, rotation about Z as shown below:
Finally, an intersection point (PT4) is used to control Y translation, along with X origin and Y origin. Since the CAD models origin is at the bottom corner, Z origin is shifted 62.5 mm (which is the distance between the bottom and top surfaces of the part) to create the same PCS.
Once the user clicks on Preview button, in Setup Alignment dialog, PCS will be translated to defined position in the dialog as show below:
Once the user clicks on OK button, the current alignment will be created. At this point, PCS represents the physical location of the part origin relative to MCS position, but the CAD model still located at the MCS where it was imported for the first time. In order to translate the CAD model to the current alignment, go to Alignment Menu - Lockpart, and the CAD model will be translated to PCS as shown below:
Important Note: The Lockpart command in Capps is an extremely useful option when dealing with any type of nominal CAD data, whether it is a CAD file, or simply nominal point data.
When creating nominal data for the first time, whether using CAD file, or by entering nominals, it is absolutely necessary to use Lockpart command before creating the nominals.