On 2010-05-26, Robert Swinney wrote:
Don sez,

some snip and,

"And in particular, I would go for split points instead of the
usual chisel points."

Don, as usual, I agree with your basic suggestions but I fail to see the
facility of split points for the basic home-shop craftsman. Most of us
use drills in machine tools and thus the necessity for easier
penetration of a split point is not a big factor.

Penetration is not (though I keep a 1/2" diameter split point
near the lathe so I am less likely to cause a workpiece to slip in a
collet from the drilling force before I start boring.

But ... the freedom from walking is a major benefit. I've
managed to drill a 1/16" diametrical hole in a 1/4" shank in an awkward
place using a hand-held electric drill. A normal bit would have
frequently walked around the curve of the 1/4" diameter workpiece. (It
was the shaft on a bearing for a overhead garage door which kept walking
out of the bracket. This allowed me to add a washer and a split cotter
pin to hold it in place. It would have been better drilled in a drill
press -- but getting it off the door and to the drill press was quite
awkward, and I had recently picked up a new set of split-point
fractional sized bits at a yard sale.

Any time you have to drill a hole in a precise location, and
can't use a spotting drill for whatever reason, a split-point takes less
of a center punch -- or often none -- to give a stable start.

And as for the drilling force not being important -- the more
force, the more likely the drill is to bow (especially if a jobbers
length or longer) and start drilling off at an angle to the desired
hole. So my preference is for screw-machine length with split points
for starting the hole at least -- and for deeper holes I'll switch bits
to a jobber length to finish the hole once the depth of the hole is
helping to guide the bit straight. (Even so, the bowing force causes
the flutes to cut the hole a bit larger on one side once it starts.) If
I were to buy my "Made in USA" 115 piece drill set again -- I would go
for split points there, too.

Also -- reducing the force (by getting rid of the chisel point)
means that when drilling through a workpiece in the lathe, you are
generating less heat -- so you aren't stuck waiting as long for the
workpiece to cool back down so you can get an accurate measurement.

FWIW The "bright finish" which I also suggested has the benefit of
clearing chips out with less heat.

A TiN coating can improve performance in certain materials --
reducing the built-up-edge -- but is not needed for general work.

Enjoy,
DoN.

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