3 & 4 flute drill bits

[geryuri2]

The drills in the above photo are center cutting, pretty unusual. Core drills on the other hand are not (center cutting) they require an existing hole. Classic first year machinist question "what is a core drill?" (A) It is used to enlarge an existing hole, like one cored into a casting; hence the name. They are extra rigid, to reduce wander due to the core in the casting not being precisely placed.

 

[JeepsAndGuns]

As requested, heres a picture of the tips of the ones I have.

 

[Terrywerm]

Thanks for this thread and responses, everyone! I learned something new!