With the trapezoid petals cut to size, what would be the best way to get the 22.5-degree chamfer on the edges?

Since I have little in the way of tools, I suspect that paying somebody might just be teh easiest. I have a router, and can get the 22.5-degree chamfer bit, but holding the work so as to reduce opportunity for a mistake is a bit of a task I think.

Anybody feel like taking a shot? trade for ____? I have anything from tubes to amps to put on the block. Or if somebody shares some magic, I'd be off on my own.
cheers,
Douglas

• Cross Cut Sled

If you have router with a 1/2" collet and a router table with fence, these router bits would be a great option. Not as cheap as a homemade jig, but hell of a lot easier. For your 8-sided horn, you want the middle one.

gar.

• Birds mouth router bits