For Scarfing things like spray rails, gun wales and in wales you can't beat Tracy O'Brian's little jig. it's fast amd acurate every time. I've built one and as usual I improved on it a little. The improvement was a substition of the key piece that rides in the slot of the tablesaw. he say's to use a piece of hardwood, but it will still shrink and swell. It's a adjustable alum piece that you get from the woodworking supply house's for building jigs. You can adjust it to a nat's behind and it will not stick or let the jig wiggle.
http://www.tracyobrien.com/article.asp?a=show&id=2
Here's a pix.