> I am having a go at making my own singing bird.  I am using some
> drawings to guide me along but have a question about a certain part.

Good luck on the project.  I am sure it will be challenging and
enjoyable.  I thought I would share a clock out of our collection that
may interest you.  It is a singing bird clock made by Emilian Wehrle of
Furtwangen, Germany.

Emilian Wehrle was better known for his trumpeter and flute clocks,
but did make a small number of these singing bird clocks as well.
The clock is signed and dated by Emilian Wehrle on the backboard 1876,
along with the information on the first purchaser.

What may be of interest to you here is the size of the mechanism.
Most other singing bird mechanisms are very small, but on the Wehrle
singing bird clock everything is much larger.  An example: each bellows
is 10" long by just under 2.5 inches wide, and there are two of them!
The brass movement alone without the pneumatics is 7" x 9".

If you are interested in photos of a singing bird clock there are two
examples that can be found on my web site at http://blackforestclocks.org/ 
A direct link to one of there is here:
  http://blackforestclocks.blogspot.com/2009/12/rare-emilian-wehrle-singing-bird-clock.html 

If you would like close up photos or details of anything feel free to
contact me.

Best,
Justin J. Miller
http://blackforestclocks.org/