> ...the central two spreading (I supposed) to leave a gap.

The central two actually confuse me a bit.  This is the only one I've
ever seen with two central pieces -- all the rest show only one.  But
judging from the metal reinforcement plate, this batissoir was worked
very hard, and the doubled middle may have been for added strength.

> If I remember Clive Kilby's book correctly, English beer coopers would
> do the same task by putting a big hoop on the spread-out end and then
> tilting it to draw the staves in. Sounds simpler but its probably even
> harder work that way.

I'm glad you mentioned this.  Kilby doesn't give much mention to drawing
the ends of the staves together after the barrel has been raised.  In
The Cooper's Trade, he mentions, but does not illustrate, the "Dutch 
hand"
and the "Spanish windlass."  These are variations of looping a rope 
around
something and putting a stick through the rope so you can twist it 
tighter
(like the twisting stick in older bow saws).

This probably works well enough on slight barrels and slack cooperage, 
but
Kilby also writes (in Coopers and Coopering) that stout and extra stout
casks had staves 1 1/4 to 1 1/2 inch thick.  A Dutch hand won't do for 
staves
this thick. I always thought Kilby must have been talking about the 
batissoir.

After reading your post, I went through my photos and drawings, and 
found
that none showed the devise in English use.  Curious.  It is common to 
German,
Spanish, Italian, Portuguese and French coopering.  The first one I ever 
saw
was in the hands of a cooper who worked in one of the Napa cooperages 
(about
30 years ago).  It (and a somewhat simpler form) is illustrated in 
Diderot.

I suspect that by Kilby's time, this tool had been replaced by a 
mechanized
tool, one in current use in commercial cooperages.  The French had been
experimented with a number of steam driven tools for mass production by
the mid 1800s.

If anybody has more information on this issue I'd love to see it.

Mike in Sacto