...just don't do it.
I was helping my nephew build his electric guitar. Today we finally got around to shaping the body, which is 1-3/4" ash. We band-sawed close to the line, then double-taped the template to the body and took it to the router table.
The hourglass shape meant that some cuts skimmed over the tops of the leaning-away grain, but just as many needed to confront grain rising against the bit. I did all the easy cuts first, and attempted climb cuts with the rest. Small mistake, and then big mistake. I had a few little scares when the big, heavy part skipped a little, but more or less held my own...
...until I got to the U-curve at the cutaway part of the guitar. I went a little too far past the bottom of the U, and backed into a big problem: about an inch of borderline blew out in a dangerous instant, leaving 5/8"-long shards sticking out like Lady Liberty's crown. Hard, angry shards. Fortunately, the body and template probably weigh 8 pounds, so I was able to avoid a projectile.
I went into damage control mode. I decided to do the rest of the trimming to the line with spokeshaves, and so far the results have been better than I expected (hooray: a silver lining here; I've been spokeshave-challenged before this). Also, I actually used a coping saw to whack back the errant shards in the blowout area. We're also going to turn to convex sanding blocks for the curves that are more acute than my curved shave. With those three adaptations we hope to finish the body's edge. And I have given up any dream of using a 1/4" rounder bit to ease the edges!
But anyway, what is at about ash that just explodes like that against the grain? I have to confess I was using a two-flute straight bit (1/2" diameter, 2" length of cut). I might have had better luck with a compression spiral bit, but even Whiteside's $175 compression bit only cuts 1-1/8".