Check out this post from @Bartman from one of my topics, basically for the same reasons (feeds and speeds). His breakdown of chipload and feedrates greatly reduced my issues and gave me a better understanding that I was really just using the wrong bit too fast for the task (and the cnc for that matter) (2 flute 1/4" endmill, dewalt router → too fast for bit) and that using a single flute 1/8" endmill I was able to get a decent chipload/feedrate combo that worked well.