Around the periphery of the vacuum table on the thermoforming machine, the previous owners built a perimeter using L-brackets. The presence of the frame made sense to help seal in the vacuum. The mystery is the height: The vacuum table and its surrounding frame are the same height as the combined height of the top and bottom parts of the frame holding the workpiece. We had expected the vacuum table to be aligned with the bottom part of the frame, since that's the height the workpiece will be held at. A frame this high would have impacted the workpiece on the way down. We're left scratching our heads figuring out why this is desirable.
But that mystery isn't important right now. Since we intend to put this machine to work on low-volume hobbyist projects, we will want to change the size of the workpiece frequently. This would be difficult with the existing system, since changing the size of the workpiece means changing the surrounding frame, greatly increasing the up-front setup work. It might be fine for a commercial production machine but such a barrier on a hobbyist machine would probably mean we'd be too lazy to actually use it.
We're bouncing around a few ideas that should make it easier to change the size of the work piece in the machine. All of those ideas are incompatible with this existing taller-than-expected frame, so it needs to be removed.
A few jabs with a metal putty knife got things going and the frame popped off shortly afterwards.
Then the tedious part starts: the putty knives went to work scraping off the sealant that was liberally applied to the bottom of the frame.
Part of the motivation to invent a new vacuum sealing system is visible here: this surface is quite scratched up and rusty. To make it seal properly with the old system, we need to remove all the paint, sand things flat, and put on a new smooth coat of paint. Unless we can avoid that work with a clever new sealing system.
(Cross-posted from NewScrewdriver.com)