Setting Up a Vacuum Press Air Bag

by Jeff Reed - The Veneer Works

Note: I've included a list of definitions at the end of these instructions.
If you find any words/phrases you don't understand, check there.

A. 3/4" Melamine. This piece is cut to fit inside the air bag. Allow at
least 1" clearance around side edges and back edge. The front edge will have to be
determined, to allow for sealing the bag. Put a small radius on all edges and
corners to prevent puncturing the bag. When this piece is completed it will remain
in the air bag permanently.

B. Saw kerfs cut into melamine. Make kerfs about 1/8"
deep. Spacing is only critical through the hole locations. The kerfs allow for
even pressure when the air is evacuated.

C. These are holes drilled through the melamine. The size and spacing are determined by the air bag itself. The evacuation holes on the air bag are on the bottom side of the bag.

When setting up the air bag, use a flat surface which is larger than the
air bag itself. The bench top needs to have two holes drilled through to
allow for evacuation hoses to be attached. Roll out the bag onto the bench
top with holes in the bag facing down. Hook up all hoses to bag. Carefully
slide permanent bag platen into bag. Make sure that the holes line up with
the evacuation tubes in the air bag. After connecting hoses to bag and
pump, seal up the bag, turn on the pump and do a test run. When the air is
evacuated there should be no air pockets remaining in the bag. After a
successful dry run, jump up and down and cheer.

When you are finished patting yourself on the back, you should know you
still are not completely ready to press.

The next step is to cut a bottom skid plate. I recommend 1/2" MDF. Cut
the skid plate the same size or slightly smaller than the permanent bag
platen. Slightly radius all edges and corners. This plate is re-usable
during all pressing operations. It gives the pieces to be pressed a flat
surface for equal pressure distribution. If you want, do another dry run
with the bottom skid plate in the bag.

Next I recommend a test press. For glue application, I suggest using a
1/2" nap, 9" roller. As for the glue itself, for basic lay-US Postal Service, I suggest a
standard P.V.A. glue. I prefer white glue because its viscosity is lighter
and it spreads easily.

Set up is key in any gluing operation. It makes the entire operations
easier if you have a second bench set up at the same height of the air bag
bench, to allow the skid plate to be easily loaded and unloaded.

Remove the skid plate from the bag. Set the backer veneer on the skid
plate. Remember if there is paper tape on the seams, the tape always faces
out; do not apply to the glue surface.

Roll the glue on the back side of the core, in a consistent spread. Do
not spread it too thick or it will have a tendency to bleed through to the
surface of the veneer. Flip the core onto the backer veneer, roll glue on
the face side of the core. Apply the face veneer onto the core, then set the top
plate on. Slide the skid plate and lamination into the bag, seal it up and turn on
the pump. When the air is evacuated, the pump should automatically shut off.
Check the air bag for leaks ? if you find any, seal them ? you don't want the pump
to run continuously.

Time to play the waiting game now. Allow the piece to press for at least an
hour and a half. Standing and watching it press won't make it set up any faster (I
know, I've tried), so go have a beer and relax.

After completion of the press cycle, remove the laminated piece. If all
procedures were followed correctly, you should have an MDF panel with veneer
applied to both sides.

If the core is glued to the bottom skid you forgot the backer. If it is
glued to the top plate, you forgot the face veneer. If the veneer falls off, you
forgot the glue. Finally, if your lamination is 1/16" thick, you forgot the core.

Air bag pressing is not as complicated as it sounds. After a few
presses, it becomes second nature. It serves as a versatile tool for both
small and large shops. Air bag pressing is not limited to flat presses. I
personally use mine for curved work, half round tubes, for example. Curved
work set up is more involved ? give me a call if you want to attempt it.

I can be reached at 303-571-5798 for further questions.

Jeff Reed
The Veneer Works

Definitions:

1) Core stock. This is the actual substrate to which the veneer is applied.
I prefer to use MDF because of its uniform density and thickness. It is
available in 1/4", 1/2", 3/4", 1", and 1 1/4" thicknesses. When cutting out
a core, it is advisable to size it larger than the final panel, to allow for
final sizing.

2) Face veneer. This is the actual veneer which is the most visible.

3) Backer veneer. This is the veneer applied to the back side of the core
stock. It adds balanced to the finished product and prevents warping.
Backers can be visible at times (on doors, for example). I always recommend
using the same species of wood on the backers, whether it is visible or not. When
making up the face and backer veneer, you should allow 1/4" overhand of the core
stock. This will prevent the piece from bonding to the skid plate and top plate.

4) Top plate. This is used as a cover sheet for the lamination. Top plates are
cut out of 1/2" MDF. They should be cut so they are 1/4" larger all the way around
than the actual core stock to be pressed. Remember to slightly radius all edges on
the top plate to prevent puncturing the air bag.