"Bill Schwab" wrote in message
nk.net...
snip---
How much of a hole do you drill with the center? I've been following
Harold's recommendation to touch the work to make a mark and check the
location before doing further damageg - two fewer pieces of scrap and
counting.

Congratulations on practicing one of the best tricks in the trade. You have
obviously already reaped your reward, which is the reason those of us that
use the same trick, use it! g

If where I intended, I enlarge the mark, but my gut sense
reading the above is that I should be doing more??

Bill

Yes, you should be doing more-----if the hole size is critical, or you just
want to turn out better work.

As you experiment with hole drilling, you'll come to realize that the depth
and size of the center drill (which I always use, I don't use spotting
drills) has a profound affect on how the drill starts out. I've never
really concluded anything concrete-----sometimes a quite large starter hole
is needed, other times a small one seems to work well enough. I use center
drills from an #00 size up through #5, depending on the work at hand. Only
experience, which you'll get by trying various combinations, will teach you
what works best for your circumstances.

One of the things you often encounter is if your center drill is too large,
the drill chatters like hell getting started. Controlling drill speed and
feed rate will generally overcome any problems inherent with that scenario.
Again, the circumstances of the job at hand may dictate the necessity of the
large starting hole, so you have to learn to deal with the problems.

Make sure your drills are properly sharpened----and don't use one that has a
dull edge, especially if it's only on one flute. That's a sure recipe for
an oversized hole.

When hole size is critical, or you just plain want things to work out as if
you're a skilled craftsman, start your hole with a center drill, drill
undersized, then open the hole to the desired size. When drilling with
fractional drills, you usually use a drill that is 1/164" under the desired
size to drill the hole, which should allow enough for the hole to clean up.
If it doesn't, there's something wrong with your process, usually the drill.
You don't want to leave too much in the hole, otherwise the cutting forces
can overcome the margins of the drill (which are circular ground and have no
relief angle) and still yield an oversized hole.

When drilling with number drills, pick a drill that is maybe .010"/.005" or
so undersized for the starter hole, then open to size. The smaller the
hole, the smaller should be the difference between the two drill sizes.
Don't leave too much for the second drill, but make sure there's enough left
for the drill to open the hole to size.

Drills rarely provide a straight, round hole, but by double drilling as
suggested you can usually get a decent hole that will be within a couple
thou of nominal size, and will be as round and straight enough to be
acceptable for most applications.

Drills that are sharpened off center will generally wing, creating an
oversized hole at the mouth, but slowly moving towards center as the margin
of the drill is forced towards center. You get a bell-mouthed hole.

If you're not adept at hand sharpening drill bits, it's not a bad idea to
have a drill pointer of sorts to help keep your drills in good working
order. Sharpening by hand is very good, but generally requires
considerable experience before your efforts are acceptable. A careful
hand can even split points.

Keep your drill shanks free from burrs. Hit them with a file if you raise
one, so the drill is held concentrically in the chuck. Remember, drill
shanks are not hardened, so they burr easily.

Harold