Cutting, gluing oblique angles

Folks -
I have a 4 equally sided pyramidal lid, apx 14" square, that rises at an angle of 25 degrees - how the hell cut accurately and glue it up?
Based on the compound miter calculator ( http://www.scarletta.net/WoodJoy/compound_miter.html ) I need to set the crosscut at 42.19 deg and the bevel at 17.39 deg. My material is only 3/8" thick, and I am just doing a butt-joint with gorilla glue. I glued up the panels in pairs, and then glued the pairs. I taped the face of the joint and then had a backer board of the complementary angle behind it for clamping - all pcs were the same size and each pair of panels mated up in the same plane, so I thought I was okay... And then...
Now the top isn't flat - it has "cupped" almost 1/2" across the middle and sallies like a rocking horse when you put it on a flat surface... NOT what I was after.
So, here are my obs and questions: The scales on the saw, especially the bevel cut (Bosch 4412) don't allow for that sort of precision. I am thinking that I am not hitting the same exact angles when I change the orientation of the saw blade for the different cuts, and this is allowing errors to creep in when I think that the two mated panels, or panel sets are at their correct angles. There really aren't any user adjustable stops that would give me that dead on accuracy I'm after. Because of the triangular shape of the panels, I can't flip the wood around for every orientation I would need in lieu of changing the saw angles.
For glue up, I am thinking that after I have the panel sets glued up, I might be able to clamp the panel pairs down onto the tablesaw so that everything will stay flat.
I would also like to reinforce the joinery for these shallow thin panels, but think that a biscuit would blow out. I am chicken of using dowels because of the absolute discrete alignment concerns.
Look forward some feedback on this one....
John Moorhead
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"John Moorhead" writes:

<snip a tale of you can't get there from here>
IMHO, angles are worthless, use actual dimensions to determine bevels.

You are working with what at best can be described as a 2nd class adhesive.
IMHO, it is totally worthless overpriced snot.
If you want good joints, no biscuits req'd, use epoxy filled with microballoons.
When the wood has returned to compost, the epoxy & microballoons will still be in service.
HTH
Lew
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Lew Hodgett wrote:

Overpriced, yes. Totally worthless? No. I finally found a use for it plugging various gaps in the walls of my shop.
--
Michael McIntyre ---- Silvan < snipped-for-privacy@users.sourceforge.net>
Linux fanatic, and certified Geek; registered Linux user #243621
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Go to the next WW show and get that guy from IN-LINE industries that demos the "Dubby Jig" to cut it for you...
John Moorhead wrote:

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