Piotr Barcz asked about how long of a roll (time-wise) would fit on
spools with various size flanges. You can calculate the length of
paper if you know the inside and outside diameters of the paper roll,
and the thickness of the paper using this formula:

Length = (Do^2 - Dc^2) x PI / (4 x thickness)

where Do^2 is the outside diameter of the roll squared, and Dc^2 is
the inside (core) diameter squared, and Do, Dc, thickness and Length
all in the same units.

The cardboard core of a typical QRS spool has a diameter of about
0.845 inches. Older piano roll paper is about 0.003" thick, but the
paper that Piotr and I have been using with our laser perforators is
between 0.0024" and 0.0031" thick (the kraft paper that comes in
1200-foot rolls is the thicker kind).

So a small 2" diameter flange will hold about 89 feet of the thinner
paper or 69 feet of the thicker paper. A large 2.55" diameter flange
will hold about 157 feet of thinner paper or 121 feet of thicker paper.

But the time it takes to play through a certain length of paper
depends on the Tempo setting and also on the diameter of the take-up
spool (because the paper accelerates as the take-up spool fills),
so this is not a straightforward calculation.

The problem with too-long rolls, of course, is that towards the end
they tend to stall momentarily while playing, as the paper on the
take-up spool slips and tightens.

Bill Luecht
Danville, Indiana