To mount the blank to the lathe, I prefer to use a glue
block. This is a very secure way to hold the wood and allows
for cutting from both sides of the blank. I use a faceplate that
fits my lathe and mount a dense hardwood block to it. It's basically
a large ~3" spindle. I like to cut the center out of the glue
block and leave only a ~1/4" ring around the outside. Yes, you're
gluing to endgrain but with this very dense maple, it does a
fine job of holding. It looks like this:

To start, I
mark the center point on my blank with either a center finder
or by making an "X" going from corner to corner on my blank.
Then I use a compass and make a couple of circles larger than
my glue block. I apply glue to the 1/4" ring on the glue block
and stick them together centering it on the rings. You can eyeball
the position, that's good enough for this work.
This photo shows the glue block attached to the blank.

Here is a close up of the glue block showing the circles
and the glue after drying. I like to add some weight to the top of
the glue block until it dries. I usually do these in batches and let
the glue dry overnight.
Now let's move to Step 3, Cutting the Insert
Recess
Click here to go to Step 3