My Vacuum Press
As
a lot of people are aware, there's no better way to get even clamping pressure
than
that provided by a vacuum. I saw a jig in an old Luthier's Mercantile catalog,
and after reading
all that I could find on the subject, I decided that I needed to buy
one. So four years later, I built one.
As
you can see in The Setup, it's not a terribly pretty fixture, but it does the
trick.
The "Closer Look" photo gives a closer look at the main unit. Inside
is a radiussed work dish,
of which I have two, one for bracing tops, at a 28' radius, and the other,
a 15' radius for bracing backs.
The picture entitled "The Pump" shows (amazingly) the vacuum pump.
It is connected to
the Vacuum Press using 1/4" polyethelene tubing, the same as used for connecting
a water line to a refrigerator. A simple brass compression fitting is used make
the connection,
(see photo below) and is screwed into the side of the press into a simple drilled
hole.
The Press is made from baltic birch plywood that I had laying around the shop
for making jigs.
The top and bottom of the Press are secured in the back by a piano hinge, and
the front is held
secure by the latches in the photo above entitled "Handle & Latches.
These latches are made
for casement windows, and draw the two parts together very well. A gasket of
closed-cell foam tubing
(see photo below) circles the inside of the bottom surface to create an air-tight
seal against the top.
The top surface of the base is a sheet of 1/8" "whiteboard" from
my local lumberyard.
It has a really smooth surface which is good for getting a good seal under the
self-adhesive foam tubing.
The top has a sheet of 1/16" rubber secured to the top of
the frame by a sheet of plexiglass and screws.
There are several small holes in the plexiglass to allow air to enter the space
between the the
plexi and the rubber sheet when the pump draws the rubber sheet down onto the
work.
As you can see by the photo entitled "Corner Construction" above,
I used the baltic birch plywood
to beef up the frame to easily withstand any stresses placed on it.
The other thing that is important to consider is providing a way of getting
the air out from under the
top or back, to create a good seal between the radiussed dish and the top or
back. I remembered seeing
similar setups in the shops of Alan Carruth and Thomas Knatt, and I gleaned
a little valuable piece
of information. If you slot the dish, the air can pe pulled neatly out from
under the workpiece, and it
also creates a nice solid connection with the workboard. See photo below entitled
"Slots in Dish".
