The treatise from David A. Vanderhoofven on replacing centre pins was
a welcome contribution.  As another contributor explained, "it is not
exactly rocket science."  There are a couple of additional points that
I would make, however:

Using the right sized pin is important. Usually one size up from the
existing pin is a good start.

Getting the *feel* is a matter of practice. I have found that if you
can push the pin through the flange bushings (before final assembly)
with your fingertip on the sharp end of the pin then it is too loose!
If you can just push it through using the flat end it is probably about
right.  Be careful not to over-ream bushings!

Only testing will show the proper fitting.  When assembled there should
be free movement up and down but no sideways wobble.

I have found final insertion of the pin through the jack (or hammer
butt or damper body) to be eased greatly by a quick dip in tallow to
slightly grease it.  Alternatively, run the pin though your hair.

Finally make sure that the nipped end is smooth. A quick file down will
ensure a nice neat finish.

Roger Waring
The Pianola Workshop
Solihull, England