accurate cuts?

[HomeBrewer]

I have a cheap little table saw that has a very small base. The miter attachment is not very accurate. Is there a way for me to build a jig and ensure that all 16 of my 22.5 degree cuts are accurate? I also have a 10" compound miter saw, but the boards I need to cut are 7.75"x22.75"x.75" and will not fit on the miter saw.

I made the cuts and the 8 pieces are supposed to form an octagon. They did, but I had a 5" gap. :(

[Lowell Holmes]

Set a bevel gage (a neander tool) to 22 1/2 degrees and set the miter gage with the bevel gage. You can set the bevel gage by measuring up 4" and over 1 42/64" and striking a line on a board or paper.