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Dec. 24, 1946.
Filed Sept. 22, 1945
’ 2,413,022
Patented Dec. 24, 1946
George A. Woody, Spring?eld, Mass.
Application‘ September 22, 1943, Serial No. 503,409
1 Claim.
(01. 29—1.1)
(Granted under the act of March 3, 1883, as
amended April 30, 1928; 370 0. G. ‘757)
The invention described herein may be manu
factured and used by or for the Government for
governmental purposes, without the payment to
me of any royalty thereon.
section of the end of a barrel blank showing the
non-conformity of the centering hole with respect
to the end of the drill.
Fig. 4 is a detail view of the cutting end of
This invention relates to a method for drilling 5 the single lip stationary barrel drill.
Fig‘. 5 is a longitudinal sectional view of the
bores having a large ratio of length to diameter,
lathe used for turning the ends of a barrel blank
particularly, the bore of ?rearm barrels.
In the manufacture of firearms, especially rifles
showing a warped barrel blank mounted therein
for such turning,
and machine guns, there is no more diihcult step
As is well known to those skilled in the art
than the initial drilling of the barrel bore. It 10
of ?rearm barrel manufacture, best results in
is essential that such bore be straight and con
drilling barrel bores are obtained by the use of
centrically located with respect to the barrel
a stationary single lip drill such as is shown in
blank. The straightness of the bore path de
Fig. 4. Such a drill is generally held stationary
pends largely upon the initial position assumed
by the drill. If the drill makes its initial cut 15 and is fed into a rotating barrel blank. Prior
at only a very slight angle to the bore axis, then
to drilling thebarrel blanks, however, it is cus
tomary practice to center drill each end of the
the end of the drilled hole, due to the large ratio
barrel blank so that such blank may be centrally
of length of barrel to its diameter, will be so
located in the turning machine or lathe to prepare
displaced from the axis of the barrel blank as
to reduce the wall thickness on one side to a de— 20 such blank for the drilling machine.
While it appears that such an arrangement
gree rendering the blank unusable. The problem
should produce a satisfactorily drilled hole in
the barrel blank, it has been observed that the
shape of the end of such drill does not conform
25 at all to the contour of the centering hole usually
provided in the end of the barrel. This is clearly
For the foregoing reasons it has been the prac
shown in Fig. 3. As a result’of the drill being
tice of all manufacturers of firearm barrels to
employ a barrel blank of substantially greater
fed into such an unnatural hole as well as a
diameter than necessary in order to provide suf
hole burnished and work hardened by previous
ficient stock to compensate for misalignment of 30 turning operation the end of the drill is thereby
the drilling. This procedure requires more metal
forcibly deflected from one side to the other of
the centering hole. It is this de?ection of the
to be used per barrel and increases the amount
of metal to be removed by subsequent machining
drill that is believed to be the principal cause of
operations. Hence the bene?ts obtained by the
the drill entering the barrel in a slightly non
use of forged barrel blanks are largely neutralized. 35 centric or angularly displaced position with re
Accordingly, it is an object of this invention
spect to the barrel axis. It is apparent also that
should the drill when emerging at the opposite
to provide a novel method for accurate drilling
of bores having large ratio of length to diameter.v
end fail to properly align with the centering hole,‘
It is a particular object of this invention to
it is liable to serious injury.
provide an improved method for drilling the bore 40
In this improved method for drilling ?rearm
is further complicated by the fact that few if
any barrel blanks are straight and straightening
operations prior to drilling are costly and time
of ?rearm barrels.
barrels, the need for centering holes has been
The speci?c nature of the invention as well
eliminated and accordingly one of the primary
as other objects and advantages thereof will
causes of drilling misaligned bores has been over
clearly appear from a description of a preferred
embodiment as shown in the accompanying draw 45 - In the practice of this improved method. barrel
blank i can be forged to an exterior shape as
ing in which:
1 is a front elevational view showing the
shown in Fig. 5 approximating the ?nal shape of
barrel mounted in the barrel drilling machine
the ?nished barrel. The barrel blank 5 is then
which is partly in longitudinal section with the
turned down slightly on a center drive lathe at
drill about to enter the squared end surface of 50 each end 2 and 3 to provide a chamfered surface
4 on the end 2 and a cylindrical surface 3 on the
the barrel blank.
Fig. 2 is a side elevational view of the barrel
other end. In such turning operation the barrel
blank showing the bore drilled accurately along
blank I should however be supported at two
points A and B intermediate the ends of the blank
the axis of the barrel blank.
Fig. 3 is a detail view partly in longitudinal 55 as shown in Fig. 5. The points A and Bare
preferably located approximately one-third the
thereof although of course it is readily apparent
that drilling may be started from either end of
distance of the barrel in from each end 2 and 3
respectively. The barrel blank I is then held
securely at these two points in a suitable machine
such as a center drive lathe and revolved so that
the ends may be turned down as above described
and the chamfered end faced off perpendicular
to the axis of the blank in this position.
chamfer 4 is provided on the large end 2 of barrel
the barrel blank as desired. The end 3 of blank
I is ?rst loosely inserted in collet or chuck 20
then the right end 2 of barrel blank I is placed
into the chamfered interior I5 of the end of bar
rel guide bushing 8 and is forced against the drill
guide bushing ‘I compressing the biasing spring
I 4. Bushing l’ is also forced into contact with
blank I for a purpose to be described. The loca 10 the bottom of recess ID thereby providing an ef
tion of the points A and B is an important factor
fective oil seal around drill I6 in the bottom of
in obtaining increased accuracy of location of the
recess Ill. The chamfered surface 4 on the end
drill while drilling the bore as such location mini
‘2 of barrel blank I ?ts snugly against the cham
mines the effect a warped barrel blank has on
rfered surface I5 on the front face of head II of
“run out” of the drill.
The barrel blank I with the trued up ends is
then transferred to a barrel drilling machine 5.
The barrel drilling machine 5 is a'conventional
machine which need not be fully described to il
bushing 8 thereby centering the barrel blank in
the revolving center 6 and at the same time pro
viding a good oil seal. The necessity for a good
oil seal is quite evident in view of the fact that oil
under relatively high pressure is forced through
lustrate the novel features of this invention. 20 an oil hole 25 in drill I6 as shown in Figs. 1 and 4
for the purpose of lubricating the drill and clear
There is, however, a modi?cation of the head of
ing away such chips as are formed by the drilling
such machine which is necessary to accomplish
operation. The chips are of course moved back
the drilling of the barrel blank without the use of
along the groove SI] provided in the drill, together
There is inserted in the head So. of the drilling
with the excess oil. The other end 3 of barrel
machine 5 a revolving center 6 constructed to
blank I which had been previously inserted in
receive and support the large diameter end 2 of
collet 20 is tightened therein by the hand wheel
barrel blank I. The revolving center 6 comprises
2|. Thus when power is applied to belt or drive
a spring biased drill guide bushing ‘I, a barrel
. 24, the barrel blank I will be revolved by spindle
guide bushing 8 and a pair of ball bearing races to 22 about the axis of chamfered surface 4 and
9. The revolving center assembly 6 is inserted
cylindrical surface 3. The drill I6 is likewise con
within a suitable cylindrical recess I B in the head
centric about such axis.
So of barrel drilling machine 5. The ball hear
Drilling of the barrel bore may then be ac
ing races 9 are inserted within the recess IE!
complished in this set-up without the use of cen
and are suitably spaced and retained therein to
ters. The barrel blank I is rotated by spindle 22
support the barrel guide bushing 8. Barrel guide
and drill I 6 is advanced into the barrel blank for
bushing 8 is a cylindrical member provided with
the drilling operation. Drill It can be fed into
an enlarged integral head portion II. The head
the work piece at any desired rate by hand or by
II continues out of the recess I0 of drilling ma
the Well known feeding mechanisms of the drill
chine head 5a.
ing machine. (not shown). The single-lip drill
An axial hole I2 is provided in barrel guide
It‘ thus will cut its own center at the start of the
bushing 8 through which is inserted the drill guide
bushing 1. Axial hole I2 is counterbored to re
ceive an enlarged integral head portion I3 of
drilling operation and continue throughout the
length of the barrel. Furthermore, the absence
. of a centering hole on extreme end obviates
drill guide bushing ‘I. A spring I4 surrounds the ‘
breakage of the drill point. 'I have found that
body portion of drill guide bushing ‘I which acts
this feature greatly improved the accuracy of the
against the head portion I3 of bushing ‘I thereby
drilling operation and minimizes the large spoil
tending to bias drill guide bushing ‘I out of barrel
age of barrels encountered when such are drilled
guide bushing 8. The spring I4 while biasing
by the conventional centering method.
bushing 1 outwardly also exerts counterforce 50
Furthermore, barrel blanks having appreciable
against bushing 8 thereby tending to retain bush
warpage may be successfully drilled by this
ing 8 within recess ID.
A chamfered surface I5 conforming to cham
fered surface 4 on the end 2 of barrel blank I is
provided on the insideof head II of bushing 8
as shown in Fig. 1. A single-lip drill I6 (Figs. 1
and 4) is supported within an axial hole I‘! in
through the barrel blank which avoids points of
bushing ‘I.
On the bed I8 of drilling machine 5 directly
opposite the revolving center 6. and spaced ap
proximately the length of a barrel blank there
excessive reduction of Wall thickness due to warp
age better than any other axis and certainly bet
ter than the axis 27 on which the blank would be
drilled if both ends were centered.
from a power driven collet or chuck 20 is mount
ed on a suitable bracket I9. The collet or chuck
20 is a conventional clamping member and is ar
Thus it may be readily seen that by truing up
the ends of the barrel as previously described and
drilling the bore of such blank by permitting the
method. Referring to Fig. 5 wherein a common
type of warped barrel blank I is illustrated, it is
readily apparent that the supporting points A
and B for the initial truing of the ends 2 and 3
of the barrel blank I produces a drilling axis 26
ranged to be tightened by a hand wheel 2I in the 65 drill to ?nd its own center that a barrel blank of
usual manner or by a chuck wrench. Collet or
smaller exterior dimensions may be readily uti
chuck 20 is conventionally mounted on a revolv
ing spindle 22 mounted on the upper portion of
bracket I9. The spindle is arranged to be driven
at high speed as by a pulley 23 secured to the 70
center. of spindle 22 which in turn isv suitably
driven by a belt 24 connected to a suitable power
source (not shown).
lized as the tendency of the drill to walk away
from the longitudinal axis of the barrel blank has
been greatly reduced and therefore more accurate
drilling with greatly reduced spoilage is readily
I claim:
That method of forming a ?rearm barrel from‘
The drilling of the bore of barrel blank I is
a rod-like blank having a longitudinal central
usually started from the breech or large end 75 axis, comprising, supporting said blank for rota
tion about said axis at two spaced points between
the ends of said blank, each point being approxi
revolution only, and while so supporting said
blank forming the bore of said barrel by axially
mately one-third the length of said blank from a
translating a drill from one end of said blank
along the axis determined by said formed surfaces
respective end thereof, forming surfaces of revo
lution on each end portion of said blank while ro 6 of revolution while rotating said blank.
tating the same while so supported, supporting
said blank for rotation on said formed surfaces of
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