Dave,
You've brought up several things, I'll respond to all of them and then ask some more questions. I don't see how this problem is somehow endemic to the techno system, and feel that it should work, so if you want to keep working on this, I think we can make it do what you need.
1) We don't supply all star gasket, we use a different manufacturer, but all star should be fine. I don't think a different rubber will make a difference for you.
I see a lot of people using the round profile and a harder density than I seem to be using.
2) Most people are happy with the original techno vacuum system. Most of those people used a Becker VTLF250 pump (or the newer VTLF2.250 that we even supply to this day). This is a higher vacuum lower flow system than what you have now - the becker will pull to over 25inhg when properly sealed. Even through MDF. We provided blowers when customers needed to pull through open cell materials like open cell foam, where high pressure, low flow pumps would give up due to the flow. Ordinarily, I'd say that a blower is the wrong pump for holding down acrylic, but since you're using an entire 4x8 sheet that you want to hold down, it should be fine - indeed, even a vacuum cleaner should be able to do that kind of work (until it burns out).
My shop vac did great for many, many hours and still cleans the shop and blows out the leaves.
Now, on to questions for you:
1) Are you certain that there are no gaps in your gasketing? I don't mean large gaps, I mean any gaps. You need to install the gasketing "Fat", and have any joints push into each other. That means not stretching the gasket when you install it (push down, don't stretch to insert), and when two pieces meet each other, there needs to be a small bulge, not a small gap. Even a 1/16" gap is to be avoided.
See this picture here:
https://www.joewoodworker.com/veneer...g-tape-top.jpg
That's what you want yours to look like, or even less of a gap - gasketing forced, interfering slightly, piece to piece.
I have known Joe for a number of years. Bought my Vacuum Veneering setup from him and covered for him while he was in the hospital. My gaskets are tight.
2) Why do you think there is a difference between your new plugs and the discs, when you are using them to seal the table? How do the discs work, and why are they different from the plugs?
The discs lay flat on the area surrounding the hole. The plugs only make contact around the rim of the hole. Any discrepancy in the hole and/or plug diameter will not seal well.
3) Can you confirm that when you put a sheet on the table and it drops to 5inhg, you're putting a sheet of non porus material right on top of the gasketing and not on a spoilboard like MDF or something else?
3/4" Marine Grade Plywood (MDO) right on top of the gaskets.
4) What happens if you put down your sheet and open one ball valve at a time? Maybe one table strip is leakier than another and is the culprit for the issue you're seeing? Imagine if the table weren't flat and your sheet, spanning several table extrusions, had a dip in it and wasn't meeting the surface well enough to seal?
Haven't tried that yet.
5) More to the point on 4: Did you flycut the material before cutting the grooves in? This is an important step in making a vacuum table - it must be flat, and between the material used and the original techno extrusion, unless you flycut and touch every part of the table with the cutter, it won't be.
Fly cut with Amana's $260 RC-2252 CNC Insert Solid Carbide Spoilboard Surfacing cutter.
6) Lastly, feel free to send me pictures of your original $50 plywood/shop vac setup, so we can talk about what is different between that and the system you have now - perhaps we can identify the change between the two that is causing your current system to not perform to your needs.
I will have to see if I saved any. . .
Regards,
Eric