I read with interest the replies from Don Teach and Gary Rasmussen on
making tracker bars, which described the MacKinnon method.  My question
is: How does such a tracker bar cope with the paper dust problem?

As I understand the MacKinnon tracker bar, it has no screen like that
provided by an authentic Wurlitzer tracker bar to catch the paper dust
that would otherwise be sucked into the primary valves to eventually clog
up the bleeds, etc.

Wurlitzer tracker bars are not made of solid brass.  The core is wood,
with a brass facing, about (my guess) an eighth of an inch thick or less.
As the holes traverse through the wood, they are angled and enlarged so
that when they exit the back of the tracker bar they form holes of about
3/16-inch diameter in three horizontal rows.

This back side of the tracker bar is fitted with a suede leather gasket
and mates to a matching block, fixed to the tracker frame, to which the
tubes from the primary valves (unit blocks) are nippled in the same
matching three horizontal rows.  That block is also faced with a suede
gasket.  When the tracker bar is screwed to it, a dust screen is
sandwiched between the two gaskets.

Wurlitzer used very fine-mesh brass as a dust screen.  But I find that a
better dust screen can be made out of a strip of computer monitor glare
screen.  We use that on the Seabreeze band organ, and a quick brush with
a camel hair brush removes the accumulated paper dust without you ever
having to remove the screen from the positioning studs which hold it in
place.  The old brass screen always had to be removed (or it fell off
anyway), and if you were so unlucky as to lose the screen down inside
the organ, you were in a real fix.

Matthew Caulfield