Now that all of the veneer material is ready it is time to prepare the baltic birch plywood cores. Each finished board consists of two 3/4” baltic birch center cores with a sapele veneer top and bottom. I first cut each 5’x5’ sheet roughly in half for easier handling.
The cut is placed slightly off center to be sure I get the maximum number of strips from each piece of plywood. The top shelf on my parts cart is high enough to allow large parts to pass over my jointer and table saw so I can easily move items around the shop.
I cut the plywood strips on the table saw and stack them on my parts cart along with the veneers.
I use UltraCat PPR veneer glue for my veneer work. UltraCat is a urea formaldehyde adhesive that works very well for vacuum pressing veneer. The open time is fairly long, about 40 minutes, which takes the stress off when trying to get a layup ready and loaded into the bag.
The UltraCat comes in powder form and is activated by water. A Respirator, eye protection and gloves are mandatory when handling this material. I mix small batches by weight and use a 10ml oral syringe to add precise amounts of water to the mix.
Since this table will not have an apron near the edge, it is critical that the veneered boards are perfectly straight out of the bag. I recently flattened my workbench top so I will use that as my flat reference surface.
For my platen I cut a piece of pre-finished birch plywood slightly larger than the veneered board. The pre-finished surface of the plywood will release any adhesive squeeze out. For breather I use felt strips glued to some poly drop cloth material placed on top of the veneered part.
The parts to be veneered are placed on the platen, under the breather. This whole ‘sandwich’ is slipped into the vacuum bag, then the top is weighted to assure the parts come out straight and flat. I turn on the vacuum pump and pull a partial vacuum and double check the alignment of the veneers and cores to be sure nothing was knocked out of alignment while loading. After I’m satisfied with the alignment, I pull the rest of the vacuum and check for leaks.
The UltraCat adhesive must be at 70 deg. F or higher to properly cure. My shop is in an unheated section of my basement. March in Pennsylvania is still quite chilly and my shop is right around 60 deg. F right now. To assure the adhesive will properly cure, I put a heating blanket over the parts to raise the temperature above 70 deg. F.
I let the glue set for 6 hours, then I pulled the test part out of the vacuum bag. Looks nice and straight.
-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"