I have been using a shower curtain liner for my vacuum bag. It is folded over and clamped with wood strips and spring clamps. This was really hard to get to work effectively as there were a lot of moving parts. I want to make a proper bag someday, but for now I really wanted to build a frame press. The concept is to make a frame with vinyl stretched across it and weather stripping foam on the bottom. Then I only need to set the veneer glue-up on a melamine assembly table and place this frame on top of it. When I apply vacuum, it will pull the frame tight against the table and pull the vinyl tight against the glue-up. It makes working by myself a lot easier and allows me to place the work a bit more precisely.
So I built a 2’ by 4’ frame out of some white oak from the scrap bin. This was the first time that I used pocket screws. It was fast, but really hard to get the two pieces to lay flat. Not sure I really like them. I am sure that I need to practice more. Maybe clamping better would help? I wish they had an indexing spline or something like a miniature biscuit. Anyway I recovered by sending the assembled frame through the thickness sander one corner at a time. It worked like a champ. I am impressed at the strength of the joint.
This picture shows the frame after I sealed it with shellac to make it more air tight. It is sitting on wax paper.
This picture shows the frame after adding the gasket to the top, stretching vinyl across it, and then screwing down (spalted) oak to hold the vinyl. And yes, it is still shower curtain liner. 8 mil. The screwed cauls allow it to be replaced.
I then flipped the frame over and added two strips of the gasket stripping to the bottom. This is pretty special gasket tape foam designed for this type of application. It is super dense and meant to be compressed.
And I added a new improved quick release connector through the vinyl in the corner. It has grooves in the bottom to allow the vacuum to spread around. The nature of the frame improves the way the vacuum can disperse as there is always a small triangle all the way around the frame where the vinyl cannot pull all the way down.
The test drives did not go without some problems. Mainly the frame did not always completely seal against the melamine when the vacuum was first applied. If I added some spring clamps to the two long sides, I was able to complete the vacuum. I could then remove the clamps and maintain good pressure. So maybe I will try to come up with some easy and light duty clamps. Maybe just weight might even do it.
The 8 mil shower curtain has been holding up quite well. Lots of test drives. I obtained some better breather mesh that lies between the glue-up and the vinyl. It does make things remarkably easier as compared to using flat wooden cauls. The plastic mesh also smoothes the edges and corners from poking through the vinyl.
-- -- I'm no rocket surgeon