Origin

Coordinate System Tertiary Datum

Command Activation

l PCS→Origin OriginToolbar.jpg (11907 bytes)
Keyboard Main Menu Toolbar

Definition

Origin acts on the location of the last measured or recalled feature. In the case of features with 1D locations such as 1D points the origin is established for the reported direction of the feature. An example setting the origin on a +X point establishes only the X origin. In the case of features with 2D or 3D locations, Geomet permits which axis to establish an origin in X, Y and/or Z measured directions as reported by the feature. Thus a 2D feature, such as a XY circle, can serve to set a PCS origin in X and/or Y directions. The tables below indicate the available origin combinations.

Feature Validation Tables

  1D Point 2D Point 3D Point 2D Line 3D Line Circle
Origin 1 2 3 2 2, 4
  Ellipse Plane Sphere Cylinder Cone  
Origin 2 1 3 2 2  

Notes:
1 - Sets an Origin on 1 axis.
2 - Sets an Origin on 1 and/or 2 axis.
3 - Sets an Origin on 1, 2 and/or 3 axis.
4 - Can provide Datum Bonus Tolerance values.

table 1 ,Origin based on a single feature


  4 Pt. Intersect Oval Slot Slot Web    
Origin 2 2 1    

Notes:
1 - Sets an Origin on 1 axis.
2 - Sets an Origin on 1 and/or 2 axis.
3 - Sets an Origin on 1, 2 and/or 3 axis.

table 2, Origin based on a Macro features

 

Datum Bonus Tolerance, (DBT) is available in a Part Coordinate System that has been built using a diameter as the origin. In Geomet, a qualifying feature is the Circle command. The DBT process will determine the amount of MMC or LMC available from the  measurement of the diameter. This DBT value is then included when positional tolerance related features.

Determining DBT

To determine the value of DBT available in Geomet it is mandatory to follow these steps. Our example will use a 2D XY bore as the origin for our PCS being built. Measure the bore as a Circle feature and apply a tolerance to the size. By applying the tolerance, Geomet can then determine the LMC or MMC value from the known tolerance limits.

When the tolerance has been applied, press the Origin key, <l> or the menu or toolbar equivalent. Set the origin on both the X and Y directions. During the origin process, Geomet will assign the DBT value to the projection plane, in our case the XY plane.

To better understand how DBT works in Positional Tolerance, please refer to Introduction to Tolerance and the Datum Bonus Tolerance Tutorial.