Bill, if you put the mesh outside of the platen it will equalize the pressure on the platen, but do nothing to equalize the pressure on the veneer, glue, substrate interface. If the veneer and substrate are of constant thickness, it's all good. However, the veneer and substrate often are not perfectly flat and, if they aren't, you will have areas that could see low or even no pressure. But if you put the mesh directly outside the veneer every square mm will see the same pressure and the bond will be good as long as the glue was sufficient and well distributed. Yes, if the substrate or veneer has thin spots there will be thin spots after it comes out of the bag. But I'd rather deal with that than areas with poor/no bond.
John
Interesting point. In a nutshell, the substrate on top of the veneer would dilute the pressure of the bagging. Taking that to the extreme .. sometimes (often) I veneer both sides of a substrate (panel) at once. One has the benefit of being just beneath the breather the other is pressed against the platen, which we're saying is "less effective." Presented with that task would you do two glue-ups?
"the mechanic that would perfect his work must first sharpen his tools.” Confucius
Thanks for writing this, though certainly a bit frustrating to read after the fact. That said I have used it on multiple shop sawn veneer projects without issue thus far even with wide flatsawn panels.
I typically glue them thick then plane them thin. Still, I will heed your advice as it is always on point.
Bumbling forward into the unknown.
Not sure I understand your question. I try to veneer both sides at the same time whenever possible. Sometimes I stack up two or three veneered substrates with mesh in between. And often I use no caul at all. If your bench is flat it isn't needed. Hopefully, some of that is relevant.
John