here is a video showing an abbreviated step of clearing posterior bone spurs...
https://www.youtube.com/watch?v=omgux9nUkC4
fast forward to 1:09 and you'll get the idea. And eccentric posterior bone - s pur like what some people have - is like a precipitous cliff hanger.. and it's pushing on the dura or thecal sack which I've been told is like scraping wet toilet paper to clean up the shavings following the milling step..