On Mon, 30 Sep 2013 00:08:14 -0500, Ignoramus11700
wrote:

On 2013-09-29, Gunner Asch wrote:
On Sun, 29 Sep 2013 21:35:16 -0500, Ignoramus11700
wrote:

Karl, I think that most people would use a boring bar on the lathe in this
situation. Especially since you have a CNC and can write a program to
take off a small amount in each pass.

You are NOT..NOT going to be able to use a boring bar in a 24" deep
hole thats 1" in diameter.

You might use a "Line Boring" setup...but not a boring bar. End
program. Full Stop. EnditEnditEndit.

Gun drill yes. Line boring yes, no boring bars. There is simply
nothing..nothing stiff enough to work. not even carbide.

EVen making very small cuts?
=======================

Long response

If at all possible, rethink your material requirements and
use something like sched 80/120 pipe or heavy DOM tubing.

To do this from solid stock is possible, but won't be cheap
or easy. The project divides into two parts, both of which
involve considerable construction of tools and tooling.
First getting a nominal size hole the length of the stock,
and then getting the hole to the required dimensions, finish
and straightness.

Assuming a reasonably equipped HD home/hobby machine shop,
this can be done, but the set-up, tool/fixture fabrication
etc. will take *MANY* times as long as the machining, and
the machining will likely be an all day job (or more,
depending on materials/ tollerances(yours and the machine)
==for each phase.== A gun drill is most likely out of the
question because of the high pressure/volume pump required,
leaving the traditional methods of woodpeckering the hole in
phase I, and then line boring in phase II.

FWIW -- one of the reasons a gun drill works so well is that
it is guided at the head very close to the cutting edge so
there is no side load on the shaft/shank. The groove in the
side of the head and shank is to give the coolant and chips
some place to go. This is why you must have a finished bore
several diameters deep to start so the head can guide as
intended.

Phase I -- Making the initial hole.

Two possibilities:

Use the lathe as a horizontal drilling machine, or if the
spindle bore is big enough let it extend through the
spindle.

Most likely you have to use the lathe as a horizontal drill,
and you save one set-up.

You will have to fabricate an extension drill as a ready
made unit will be prohibitively expensive. In order to
minimize tooling size, with loss of bed travel, fabrication
of a faux collet to accept the drill extension will be
required. This can mount to a face plate or trued dog
driver. To avoid "whipping," extension of the drill should
be no more than necessary at any one time, and the workpiece
should never be pulled off the drill while the lathe is
running. Most likely you can fabricate an extension drill
using a 36 inch piece of 7/8 or 3/4 W1 drill rod [silver
steel for our brit posters]. Get a 63/64 Silver and Deming
drill, turn the shank to 3/8, and silversolder or epoxy in a
counterbore in one end of the drill rod. The counterboring
of the drillrod will be much more accurate and easier if you
fabricate the faux collet first and machine it on the face
plate or trued dog driver,== which should remain in place
until this phase of the job is completed for maximum
accuracy.== The faux collet is simply a plate, c. 1 inch
thick that can be bolted to the face plate with a slot
across the bore to allow a 3/8 shcs to pinch the loose side
down on the drill extension so it can be adjusted in/out
without losing zero. Because the end of the extension will
most likely extend beyond the end of the spindle, whip is a
danger, and will effect accuracy. Speed should be limited,
and it is worthwhile to fabricate an second chuck or spider
to fit the outer end of the spindle with set screws to
center the extension. Be careful of the screws as these will
rip skin and meat off in a heartbeat. Bushings to fit
between the spindle bore and the drill extension when it is
moved beyond the rear chuck can be very helpful. These can
be delrin as there is no great load as long as the shaft
remains centered.


Phase II -- to line bore a 24 inch hole, you will require a
lathe with a minimum of 50 inches between centers, with 54
or 60 even better to provide some working room. you will
have to fabricate a between centers line boring bar 50 to 60
inches long of a diameter just under one inch with adequate
chip/swarf clearance. You will need to provide a high
pressure/flow [not as high as required for a gun drill but
far greater than the normal home shop swamp cooler] to
insure adequate lubrication, heat control, and chip
evacuation. To minimize deflection it is a good idea to
drill the line boring bar for two tool bits in order to
minimize the off center or bowing forces on the line boring
bar. Most likely for ease of fabrication, round tool bits
should be used. These should be small as the holes are in
the weakest part of the bar and the clamp screws should not
be too big either. The bar should be accurately centered at
both ends, and should run between centers with a solid
center in the face plate or driver and an antifriction
center in the tail stock to eliminate the need for
lubrication. These are a right bitch to adjust as one tool
trails the other and you want the tools to have equal chip
load, i.e. the "rear" bit, which depends on which way you
are feeding, should take as deep a cut as the front tool.
There is a minimum depth of cut/feed rate, depending on the
material/condition for continuous cut and good surface
finish. You will also need to fabricate a boring table,
which replaces the compound [top slide for our Brit posters]
on the cross slide. The work piece [hole] *MUST* be
concentric to the lathe spindle axis, which again is a right
bitch to set up ( be sure you have *LOTS* of shims and
*LOTS* time) [If you use the lathe as a horizontal drilling
machine you only have to do this once.]

http://www.use-enco.com/CGI/INPDFF?PMPAGE=899&PMCTLG=00
http://www.use-enco.com/CGI/INPDFF?P...MITEM=301-1058
http://www.use-enco.com/CGI/INPDFF?P...MITEM=383-7005

Let the group know what you decide, and good luck