I use a vacuum press when veneering various things. Usually it's 3/4" MDF or plywood as my substrate. Can I veneer both sides at once or do I have to bag it twice? Also, does anyone have a trick to preventing glue squeeze-out from getting on the bag? It's sticking in some places and leaving an indentation on the next piece I press. I cover the paper breaks on the edge and it allows the glue to seep through.
From contributor T:
I would suggest that you use shrink wrap on the edges.
Squeezing the pieces together, even 4x8's, I'd rotate the piece(s) on edge so the caul is down on the table and the weight of the substrate would hold the veneer flat enough until it was in the bag. Always lay down your backer side first, especially if your face has any kind of geometric matches or inlays.
Where is the glue squeezing out from? You may be using too much glue. You should get just a faint bead along the edges and little to none through the face. If you’re veneering porous material, such as quarter-sawn oak or wenge, you may want to consider an adhesive that has a shell-flour filler which practically eliminates bleed through. CP Adhesives makes a product called MPA veneer designed exactly for this purpose.
The caul can be as thin as 1/4" (I suggest no thicker than 1/2") and should overhang the sides of the substrate by no more 1/4" all the way around. In situations where you are using veneers of varying thicknesses on the same plane, use a rubber gasket (roofing material works great) between the veneer and the caul. Also, melamine works well for a caul since glue doesn't stick as well to it. We buy caul material by the unit, but only when it is damaged or being liquidated. We typically pay between $3 to $7 a sheet for this material. Remember to round over the edges of the caul before placing it in the bag.
Using a caul will prevent indentations in the veneer, and will provide a better and flatter lamination.