11-21-2021, 08:02 PM
I always veneer both sides of a panel at the same time. That keeps the moisture in balance so the panel stays flat. I use Weldwood Plastic Resin Glue most of the time, although I can't seem to find it anywhere at the moment. Fortunately, I still have a pail. If I couldn't get PRG I'd use Unibond 800 or West Systems epoxy. I only use shop sawn veneer and Better Bond and other aliphatic glues aren't rigid enough. I learned that one the hard way.
There's no need to use cauls for vacuum bagging. I use a piece of Melamine on the bottom. I put a piece of plastic window screen on top of the Melamine a layer of sheet plastic on top of that and then and lay one layer of veneer on that. The veneer is cut to be the same size or slightly smaller than the substrate. I apply glue to one side of the substrate, either Baltic birch or MDF, flip the substrate over onto the bottom layer of veneer, add the glue to the top side of the substrate and then place the top layer of veneer on top, and secure the registration of the veneer layers and substrate with blue tape in a few places. Another layer of sheet plastic goes on top and then another layer of window screen. Then I slide the Melamine carrier into the vacuum bag, close it up, and turn on the vacuum. The window screen assures that the vacuum reaches every sq mm on both sides of the panel so even if there's a low spot in the substrate or veneer the veneer is still pressed tightly against the substrate with no chance of bridging.
I trim the panels to final dimensions after the parts come out of the vacuum bag. If you start with panels at their final dimension then of course your veneer needs to be larger than the panel and that means you need to use a top caul to prevent the bag from cracking the veneer where it hangs over the substrate. The other issue with that approach is that you have to clean up the glue squeeze out with a router, etc. By trimming the panel to size on the table saw after vacuum bagging you don't need a top caul and it gets rid of the squeeze out with no extra work. No top caul also allows you to easily put parts of different size into the bag at the same time.
John
There's no need to use cauls for vacuum bagging. I use a piece of Melamine on the bottom. I put a piece of plastic window screen on top of the Melamine a layer of sheet plastic on top of that and then and lay one layer of veneer on that. The veneer is cut to be the same size or slightly smaller than the substrate. I apply glue to one side of the substrate, either Baltic birch or MDF, flip the substrate over onto the bottom layer of veneer, add the glue to the top side of the substrate and then place the top layer of veneer on top, and secure the registration of the veneer layers and substrate with blue tape in a few places. Another layer of sheet plastic goes on top and then another layer of window screen. Then I slide the Melamine carrier into the vacuum bag, close it up, and turn on the vacuum. The window screen assures that the vacuum reaches every sq mm on both sides of the panel so even if there's a low spot in the substrate or veneer the veneer is still pressed tightly against the substrate with no chance of bridging.
I trim the panels to final dimensions after the parts come out of the vacuum bag. If you start with panels at their final dimension then of course your veneer needs to be larger than the panel and that means you need to use a top caul to prevent the bag from cracking the veneer where it hangs over the substrate. The other issue with that approach is that you have to clean up the glue squeeze out with a router, etc. By trimming the panel to size on the table saw after vacuum bagging you don't need a top caul and it gets rid of the squeeze out with no extra work. No top caul also allows you to easily put parts of different size into the bag at the same time.
John
