Tracker Actions in Organbuilding.

Hallo all,  Bill Chapman mentioned 15" trackers in the MMDigest two
days ago, and was corrected by Harold Mueller the following day with
a footnote from Robbie.  Well, Bill could be right; I've made trackers
only 4" long.  But first let's establish what a tracker is.  In English
organbuilding terminology, a tracker pulls, and a sticker pushes; maybe
on your side of the pond trackers and stickers are all called trackers.

 [ Stickers push the wippens in a vertical piano, so I guess we use
 [ exactly the same terms and definitions here in 'The Colonies!'
 [ -- Robbie

So, on a typical two manual organ with Swell and Great departments,
the great soundboard would be above the manuals, therefore the vertical
strips of timber, whether they be round- or flat-shanked, would be
pushed upwards by depressing any key on the Great manual.  Because
the width of the keyboard is considerably less than the width of the
soundboard, a device known as a splayed backfall beam is used to fan
out and reverse the upward push of the stickers into a downward pull.
At this point a series of tap wires called "Pull Downs", connected to
the ends of the backfall beam levers, pass up into the bottom of the
soundboard and connect to the pallets.  Okay so far?

Now the Swell department is usually behind the Great soundboard;
this is a bit more complex to describe, but here goes.  The vertical
stickers in this case are perhaps only 3 or 4 inches long, and their
upward motion is converted into a horizontal pull by means of a "square
action".  At the rear, just below the Swell box, a second square
action converts the pull into a push once more, and again the vertical
stickers are pushed upwards.  For the same reason as the Great, there
is a splayed backfall beam to fan out and reverse the push into a pull,
with the usual pull downs going up into the soundboard.

The pedal board very often has the longest trackers of all, sometimes
extending 20 or 30 feet to the pedal section at the rear, the trackers
being supported on rollers at various positions to stop them dragging
on the floor and reduce friction.

Because they push, stickers are limited in length to 15 to 20 inches;
any longer and they become unstable and buckle sideways.  Trackers
also are governed by constraints: the longer they are the heavier they
become, thus requiring the addition of return springs.

Incidentally I've read parts of Audsley's book and was able to
releather a double riser just by following his directions.

I hope this helps but I fear I may have muddied the waters with
a complex explanation, and although a two-manual church pipe organ
is not necessarily anything to do with mechanical music as such, its
internal mechanisms are.

Sincerely
Paul Camps