The late British collector Benet Meakin had the only example I've ever
seen of a factory alignment tool for player spool boxes.  It ensured
that the two spool axes and the tracker bar were all parallel and that
the tracker bar was in line with a properly-made roll and the take-up
spool was in line with that.

It was made of brass and was quite a formidable piece of apparatus.
Most of us can achieve the vertical alignments fairly easily using a
good roll, but the axis alignment which the tool provided was really
valuable.  Usually the spool axes stay parallel, but the tracker bar
can get out of position in rebuilding.

Thinking about it from memory, I suspect all that is needed is a device
like a four-legged table, with the legs accurately made to the same
length.  Two legs are rested on the opposite ends of an empty roll core
with spool ends, mounted in position, and two on opposite ends of the
take-up spool.  The table can be lengthened to accommodate different
distances of these two axes.  If all four legs bottom-down without
rocking, the axes are parallel.

To check the tracker bar alignment, the table is shortened and two of
the legs placed on the bottom edge of the bar and the other two on the
ends of the take-up spool as before.

The brass instrument provided a reading of the "bearing" of the
paper over the bar -- in other words, how far forward from the spool
axes the tracker bar face was.  Ideas on what this dimension should be
changed as jumbo rolls came in: make it too small and jumbo rolls miss,
too large and small rolls have a lot of friction.

I would guess this instrument could be improvised by a good
metalworker.

Dan Wilson, London