Thanks for all those who gave me advice on my problem breaking 1/4" bits when routing out some countertops from 3/4" plywood on my CNC table. It turns out that the 1/4" bits were just getting too hot and I was pushing them too hard.
I went to a 1/2" shank, straight router bit 3/8" diameter and 1" long. I slowed the RPM down to 12,000 and kept the feed rate at about 36 inches per minute, and for good measure took several .2" deep passes.
The 3/8" bit barely got warm to the touch after some long runs and made nice smooth cuts through the plywood and pulled good looking chips.
This configuration won't win any speed records, but since I'm doing only a small amount of custom not production work it's fine for this job. Maybe if I get some scrap plywood I'll run some tests and see how fast I can push it. Too fast though and you start pushing the material around, stalling the router motor, breaking bits and collets and other bad things.
Tom Kreyche