Awl--

So ahm drilling holes w/ a drill/chuck/tailstock in a lathe/5C collet, in
1/4" brass, 1.75" long.

Sequence 1: center drill both ends, 3/16 drill both ends, about 1/2" in,
then 1/8" drill thru.
Awful results; very poor concentricity of 1/8" hole at the exit end.
Drove me crazy.

Sequence 2: center drill both ends, 1/8" drill (thru, or halfway from both
ends), then the 3/16" drill.
Excellent concentricity.
Sanity restored.

I endeavored in seq. 1 because I thought the thicker drill would have
inherently less drift, and that with less resultant material for the 1/8"
drill to go thru, less drift/better concentricity.
But not so.
Others experience this?

A friend says that poor results of seq 1 is likely exacerbated by the brass
material itself, and that custom sharpening of the drills would help--sumpn
like split point, but diff, he says--hasn't shown me yet.
And also that my assumption, that the cone left by the 3/16 bit is centering
the 1/8 bit, is proly not valid.
Altho it seems to me a 3/16 drill would be an adequate spot drill for a 1/8
drill.

Any idears on this?
----------------------------
Mr. P.V.'d
formerly Droll Troll

the surface left by a standard 118 point drill is very poor for centering a
new bit , very easy to start off of center

I don't think the cone left by one drill is very good at guiding another. My
method is to use the center drill, then the best drill I have of the center
drill pilot size. It seems that some of my drills are more symmetric and
drill straighter than others. Those I have resharpened {and those from
China} are sometimes not in this category :}.
Don Young
"Proctologically Violated©®" wrote in message
...
Awl--

So ahm drilling holes w/ a drill/chuck/tailstock in a lathe/5C collet, in
1/4" brass, 1.75" long.

Sequence 1: center drill both ends, 3/16 drill both ends, about 1/2" in,
then 1/8" drill thru.
Awful results; very poor concentricity of 1/8" hole at the exit end.
Drove me crazy.

Sequence 2: center drill both ends, 1/8" drill (thru, or halfway from both
ends), then the 3/16" drill.
Excellent concentricity.
Sanity restored.

I endeavored in seq. 1 because I thought the thicker drill would have
inherently less drift, and that with less resultant material for the 1/8"
drill to go thru, less drift/better concentricity.
But not so.
Others experience this?

A friend says that poor results of seq 1 is likely exacerbated by the
brass material itself, and that custom sharpening of the drills would
help--sumpn like split point, but diff, he says--hasn't shown me yet.
And also that my assumption, that the cone left by the 3/16 bit is
centering the 1/8 bit, is proly not valid.
Altho it seems to me a 3/16 drill would be an adequate spot drill for a
1/8 drill.

Any idears on this?
----------------------------
Mr. P.V.'d
formerly Droll Troll

"Proctologically Violated©®" wrote in
:

Awl--

So ahm drilling holes w/ a drill/chuck/tailstock in a lathe/5C collet,
in 1/4" brass, 1.75" long.

Sequence 1: center drill both ends, 3/16 drill both ends, about 1/2"
in, then 1/8" drill thru.
Awful results; very poor concentricity of 1/8" hole at the exit
end.
Drove me crazy.

Sequence 2: center drill both ends, 1/8" drill (thru, or halfway from
both ends), then the 3/16" drill.
Excellent concentricity.
Sanity restored.

In any cutting operation, the tool will attempt to flex to the side with
least resistance. So, in the case of a drill in a lathe, the drill will
"walk" toward the cutting edge of the drill that is cutting easier. This
could be only microscopic differences in the cutting edges in smaller
drills/tools. The center left by the previous drill in your first method
doesn't make any difference because, most likely, the portion of the
larger drill that is causing the off center walk resides inside the
portion left by the pilot drill. When you hit full cut length on both
flutes of the drill, the drill walks. By pre-drilling all the way
through, you eliminate the portion of the cutting edge causing a problem
from cutting anything, and the part of the drill edges that are actually
cutting are matched up close enough that it does not drift.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

http://www.machines-cnc.net:81/

Anthony wrote:

So, in the case of a drill in a lathe, the drill will
"walk" toward the cutting edge of the drill that is cutting easier.

Yes, but that side is rotating (relative to the work).


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de