wrote in message
oups.com...
If you get better results when the drill press is running I think you
have excessive runout in the quill.
Put a long bit ,largest diameter the chuck will take, turn drill press
on. Do you see any wobble?
If you have a dial indicator and a length of drill rod, you can check
runout better.Sometimes the chuck can be at fault, though probably not.
mike

Drilling with a twist drill in a drill press is not a suitable way to get
_perfectly_ on-center holes in anything. A) any twist drill will tend to
cut from a few tenths to a few thou oversized - partly due to lost motion in
the system and imperfect grinding, and partly due to false edges and chips
abrading the hole sides, and B) because any but a really stout drill that is
_perfectly_ ground will tend to wander a bit during its cut.

When one must have holes centered to within a few "tenths", you need to
pre-drill the hole a few (say 15-20) thousanths undersized (for chip relief
and fast stock removal) on a milling machine, then re-index (or re-check
your index of) the workpiece, and "drill" the hole with a fly cutter,
finishing with a reamer.

For most work, this sort of accuracy isn't necessary. If your drill press
spindle has more than a half-thou of runout, it needs servicing. If your
bits drill more than two thousanths over their miked-out size, they need
regrinding to center the cut. Short, stiff bits tend to wander less than
long flexible ones.

LLoyd