UCS changes based on object selected.

[tsheriff]

I have very basic 3d skills.  I have just got back into it recently.  We are creating a database of small machine parts that were laser scanned. None of the parts are layed out in a perfect xyz system so we have to rotated the ucs for each view  and reset the view for each viewport.  i keep resetting my viewports  with the view command but as soon as i select any object in that viewport the ucs changes to a different rotation.  is there anyway to stop this?

[beyoungjr]

You probably have Dynamic UCS turned on.  ACAD version??

In 2017 and 2018 look at the "Hamburger Menu" (3 horizontal bars icon at bottom right of screen.  This menu lists all possible icons for the bottom toolbar.  The Dynamic UCS icon may or may not be displayed.  Put a check mark beside it to display the icon on the bottom bar and turn it off by clicking the icon so it is no longer blue.

Also, not sure if you are familiar with the widget??? When you select a 3D part the Widget will appear at the center-mass.  If multiple parts it will appear at center of all selected.  The Move Widget is default but if you right-click the Widget coordinate symbol you can choose Rotate.  This will greatly assist in flipping 3D components without changing UCS's.

Finally, If you need to push 3D components to WCS 0,0,0 it's easy if you turn off Dynamic Input just for a moment to move partrs from the desired point on the part to 0,0,0.  Just remember to turn Dunamic Input back on because it's a valuable tool.

Hope that helps?