First you should work a mask while sanding and drilling on fiber materials.
If you want make holes bigger then 8mm you should first make a small holes and then make the hole bigger
Good working are old and not to sharp drills for metall
Better is to use drills for wood they have a centering top and cut from the outside to the inside.
Although galvanic diamant drills for ceramic work good but often they are hard to center.
Big holes for example the focuser hole can be made with bi metal hole saws for wood. first make the 5-
Then most times exspecially if the hole saw is new and sharp it is better to use the saw in left turning mode !!!
If you have more questions please ask.