Bruce in Bangkok wrote:

It is a little more commercial then I need but it
does give me an idea of how one works.

I suspected as much.
I thought that the pictures would give you the general idea. I had the
links close at hand without looking for them.
I repair, similar, and larger, stemmer-crushers and fabricate other
vineyard equipment.
For my personal use, I usually use a small antique crusher unit that
only has capacity of a few hundred pounds an hour and cam type rollers
of a cast aluminum. It will fit over a half barrel or plastic tub, I
usually do the destemming by hand. I have the luxury of using one of
the neighbors larger units, if, I need to do more.
For some winemaking styles, the winemakers are opening the rollers up
just wide enough to lightly squeeze a berry and removing the destemmer
allowing the stems to go through the rollers with only a very light
crush to the combined must of stems and berries.

Russ