Pat has it right as far as he goes. The trick is postioning the fence
right on a router table with a round over. Do the math this way: A
roundover bit is a quarter of a circle, so four roundovers will
collectively complete a circle, which is what you see when you have
rounded over all four corners of a square. If you were to route each
1/2 of the joint of a square before putting it together, then the two
halves would each use 1/2 of a roundover as measured along the cutting
surface of the roundover. Since you are making an octogon, each 1/2 of
the joint would use 1/4 of the length of the roundover as measured
along the cutting surface.

This is really a problem in trigonometry [sin(22.5 degrees)] which
gives a numerical result of 0.3826... Which means that you position the
fence so that 38.26% of the linear measure of the roundover will be
used for the cut. This will work with any size roundover.
I cannot position my fence that precisely, but you get the idea.

Jack

wrote:
The router has its limitations and this is one of them.
There are no cutters for this. You can however, with semi-sophisticated
fixturing, rout 1/2 the profile on each 1/2 of the joint before
assembly. Then sand to suit after the fact.
http://www.patwarner.com (Routers)
__________________________________________________ _______
Chad Schmitz wrote:
I'm working on a project that uses two boards that are joined at a 45
degree angle and would like the corner created to be rounded. (I'm
interested to know how to do this for any angle other than 90 degrees)
Other than using sandpaper, is there a precise way to use any type of
router bit for this. I have over 100 router bits and none of them will
achieve this for me. Most bearing guided bits are geared for a 90
degree edge prior to routing. The graphic below shows the before
(left) and after (right) of what I'm trying to solve. I've been
woodworking for over 10 years and have made countless items, but
haven't been stumped like this before.

Any help?

http://schmitz.gotdns.com/wood/radiusfillet2.jpg