I bought a set of carbide burrs at Lancair when I did my workshop.  They have been workhorses and have held up well to my constant abuse.  Lancair now sells Permagrit countersinks, which are far superior to anything I've ever used.   While I was in Redmond, the workshop had a small "Cheerio" sized bit that we used to de-core the pregreg.  I found one locally at Woodcraft.  That little tool has saved me hours of work.  Installed in a mini die grinder that I got at Harbor Freight, you can de-core prepreg in no time.

 

Mike