Central Post

The main component of the adjustment mechanism is the the central post that slides within the outer column.  To get to the thickness needed, I glued up two .75" thick pieces to make a 1.5" square piece.

For the mechanism to be smooth, it is essential to make sure all components are square and consistent thickness, without any twist.  Using a square and calipers I made sure the central post is very square and has less than 1/64" change in thickness along its length.  The outer column is made of four pieces glued up, so all of those components must be very square and flat as well.

Here is a mock-up of how the sliding mechanism will work:

Testing the squareness and fit for the outer column: