Computer Numerical Control (CNC) Drilling is commonly implemented for mass
production. The drilling machine, however, is often a multi-function machining
center that also mills and sometimes turns. The largest time sink for CNC
drilling is with tool changes, so for speed, variation of hole diameters should
be minimized. The fastest machines for drilling varying hole sizes have multiple
spindles in turrets with drills of varying diameters already mounted for
drilling. The appropriate drill is brought into position through movement of the
turret, so that bits do not need to be removed and replaced. A turret-type CNC
drilling machine is shown below.
A conventional drill press can be used to machine holes. An operator
can place a drill in the drill chuck that is secured in the spindle of the drill
press. He can then (manually) select the desired speed for rotation (commonly by
switching belt pulleys), and activate the spindle. Then they manually pull on
the quill lever to drive the drill into the work piece being machined. But with
CNC drills, this sheer amount of manual interaction changes.
A variety of semi-automated drilling machines are also used. An example is a
simple drill press which, on command, drills a hole of a set depth into a part
set up beneath it.
In order to be cost-effective, the appropriate type of CNC drilling machine
needs to be applied to a particular part geometry. For low-volume jobs, manual
or semi-automated drilling may suffice. For hole patterns with large differences
in sizes and high volume, a geared head is most appropriate. If holes are close
to each other and high throughput is desired, a gearless head can locate
spindles close together so that the hole pattern can be completed in one pass.