A1 - the Air Brake or Governor
.GIF)
Copyright 2011 by James P. Riser
A nicely functioning air brake is critical to this
project. The air brake or governor controls the speed of the entire
unit by rapidly spinning a small fan. The drag caused by the air
against the fan blades is what serves as a silent brake for the
mechanism. Without this governor, the entire mechanism would rapidly
unwind with no means of control. Such air brakes are most often
seen as part of a music box movement.
Here is an air brake on an old music box. 
The brake wheels just made are what will drive the
special worm gear of the fan. Below you may see the wheels that
I just made. And above you may see a similar wheel driving worm
of the fan.
I decided to make my fan arbor with its worm gear from
stainless steel. This should provide decades of service with no
rusting of the mechanism. With very careful reworking, a stainless
steel lag screw could be adapted to my needs. The head was first
removed and the arbor end trued in my Sheldon lathe. Everything
is held in collets for accuracy.
This is the screw
end after machining.
The next step was to do some precision grinding on
both ends of the fan arbor.
The benchtop Gorton 265 grinder was again put to work
for this. The angle was set to "0".
The wheel was dressed as required. 
The arbor was chucked
up for grinding. 
The end was ground
to form a small projection.
The projection was sized to just fit into the center
of this tiny shielded ball bearing assembly. 
Here is this bearing
mounted onto the just ground end of the fan arbor.
The other end of
this arbor has a matching projection ground on it. 
Here is what the arbor now looked like when I mounted
it on the Sheldon lathe to true up the threads.
Notice that I ground a couple flats at the fan end
of this arbor. These will come in handy when mounting the fan
later. Notice in the pictures below that I have cleaned up the
threads and polished the thread surfaces so that the brake drive
wheel will not hang up on any rough spots. These threads are now
extremely smooth. The air brake will not work if the threads are
left rough and unpolished.
Here is a closeup
view of the ends. 
Here are the bearings
and how they mount on the arbor. 
Also shown above and below is how the brake drive wheel
meshes with the threads on the worm of the arbor. Everything was
calculated and machined so that three teeth of the drive wheel
engage the worm at the same time. This spreads out energy so that
there is minimal friction in the system.
The brass fan (to
be made later) will mount on the top end of the arbor.
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