Jeff Bridges asked, "Can someone explain to me why tracker bars are
made of brass, and why not make them out of aluminum?"
Brass is smooth and wears smooth. It has sort of a self-lubricating
effect. It is also hard enough to be long lasting and it doesn't erode
too badly with repeated use. That's why its commonly used for bushings.
Aluminum has a very rough texture comparatively, and no matter how
much you polish it, it stays rough. If you used it for a tracker bar
it would grind the paper in music rolls to dust after just a few plays.
I can't think of any commonly used metal that could be worse for a
tracker bar than aluminum.
[ A variety of useful alloys of aluminum and magnesium were developed
[ for the aerospace industry and I'm sure an alloy suitable for tracker
[ bars is available; nonetheless brass (a copper alloy) is much cheaper
[ and is easily soldered (and it's prettier!). -- Robbie