My turn!  John Page has a good point about leaving the sides of the
stoppers unglued.  It certainly does make adjustments easier.  And,
I have taken apart more than one organ which had several pieces of
paper or leather tucked (with or without glue) inside the sides of the
leather to adjust the fit.  In spite of this, I often find the stoppers
either stuck in the pipes or so loose that they will fall out.

However, there is one very good reason to avoid  leaving the leather
loose.   If the leather is loose, it can creep toward the front as you
withdraw it and cause the stopper to get stuck in the pipe, especially
if it is too tight in the first place.  This is not only a problem for
future service, but a problem for tuning.  The same thing happens if
the leather is stuck to the inside of the pipe.  Of course, if it is
really loose from the stopper, it can sometimes just turn inside out
as you withdraw it.

I try to reduce the adjustment problem as follows:

 * use wood that is at the same moisture level as the pipes;

 * use wood of the same or similar type as the pipes;

 * match the grain orientation of the stopper to the orientation of
the sides of the pipe, if possible;

 * make the stoppers with the grain running 45 degrees to the surface,
with face grain on the face of the stopper; this reduces the effect of
shrinkage to about 70%;

 * measure the stopper and the pipe AND various areas on the leather
hide with a micrometer;

 * mark the stopper so that you replace it in the correct orientation;
(_Never_ use the word 'orientate' while doing this.)

 * match the shape of the stopper to the shape of the pipe -- no,
they're not always rectangular;

 * select the leather thickness and stopper size to match the size
of the pipe opening.

Finally, with fish or hide glue, it is rather easy to heat the leather
with an iron to remove it.  With the addition of a little water, it
even works after many years.  And a #11 razor knife is quite effective
at removal if necessary.

Regards,
Craig Smith