I never noticed this, but the end caps are not all the same. You may have
the caps on the wrong cassettes.

"Alan Smithee" <alansmithee@anon.anon.com> wrote

It is call 'galling', usually referring to wear of metal surfaces but it
happens with all solids.

If a substance is rubbed against itself it will raise microscopic balls and
make tiny gouges.  The gouges and balls interlock and you get a lot of
'sticktion'.

To counter this sliding surfaces should always be of dissimilar materials,
one hard material and one soft material.  The soft material can not deform
the hard material and the hard material wears the soft material to a smooth
conforming surface so the load is distributed evenly and the soft material
does not wear away after the parts are 'worn-in'.

When the cassettes start to stick then the only thing you can do is chuck
them, things will only get worse, oil won't help.  Lubricating _new_
cassettes may give a bit more life to them but eventually you will get
galling.  Try an infinitely thin coat of Vaseline, lubriplate or silglide.
The right stuff is an olefin grease [you might try butter].  I find vacuum
grease to be excellent as it does _not_ migrate.

How long have you been using the cassettes. While I prefer the plastic to the
metal one the plastic ones don't last very long.

I've never seen this but I will only use a cassette a few times before
discarding it.

My theory is that the cassette felt gets dirty and increases the chance of
scratching the film (even dust and small film particles from the bulk roll
could contaminate the felt) and that repeated use can wear enough "fuzz" off
the lips to increase the chances of fogging the film.  Metal cassettes are
easier to blow clean but even easier to misalign the lips so may be less
prone to scratching and more likely to fog the film.

I mark each cassette each time I use it, after the fifth reload I'll use it
only for non-critical applications, such as copy work or camera and lens
testing.  I also use photo-lab "twin-cheks" even when I process my own film
so I know which roll came from which cassette and can toss any offenders.  I
have a lifetime supply that I got from mini-labs that I work at.  Given to
me when we found they wouldn't stay on at 100 deg. F. (they work fine at the
temps I'm likely to use to process black and white film!).

And just a thought, not all plastic cassettes are made by the same plant on
the same set of molds so you could have problems if you've switched lids or
spools around between cassettes.  I'm very careful when I use plastic
cassettes to keep all the pieces together as I load and unload them, using
ice cube trays to keep all the bits together.