In the attached snip from a datasheet of a machine for inserting rivets in a PCB, it says that for a CNC drilled hole the size should be 0.1mm greater than the rivet outer diameter. This implies (IMHO) that for a manually drilled hole that extra 0.1mm is not necessary.

Is a manually drilled hole larger than a CNC drilled hole using the same drill?

 

Hazarding a guess here, but I think it's because CNC is more accurate than a drill bit- it doesn't use a drill but rather a cutter, and a drillbit probably has a little 'slop' (comparatively), so you add a margin to make the CNC match the drill hole equivalent. IMHO.

 

Sounds like a good guess to me, thanks.