first I draw the radius on the 2X6 using a compass
next I used a jigsaw to make the virtical cuts you see in the picture below. These vertical cuts ease the stress on the circular saw blade when you're trying to make the radial cut:
Next I cut the raduis with my circular saw. I do the cut in two passes. The first pass I drop the blade to 3/4"(about halfway through the board). The picture above was taken after the first pass.
Then I take another pass at it dropping the blade so it cuts all the way through.
It's time consuming, but the cuts came out really well.
I tried to do my first board with a jigsaw and it just came out all lumpy and horrible. A bandsaw would prob be the best tool for the job. but I don't have access to one so... Circular is the way to go for me. I did not need to remove the guard on the saw.