High speed drill system

The system includes a spindle for holding a high speed drill, the spindle being provided with longitudinal slots permitting its exterior side walls to be biased inwardly and grip the drill. Eccentric weights surround the spindle in such a manner that upon rotation of the spindle at a high speed, the weights are thrown radially outwardly to contract the side walls of the spindle by centrifugal force, thereby gripping the drill shank, the gripping force increasing with the speed of rotation of the spindle. For larger drills, a special collar is provided on the drill shank for engaging flats provided on the spindle to result in a positive locking of the drill shank for rotation with the spindle.

This invention relates generally to a high speed drill system and more 
particularly to a system for drilling printed circuit boards wherein a 
specially designed drill spindle is provided for holding the shank of the 
drill by centrifugal force. 
BACKGROUND OF THE INVENTION 
The drilling of printed circuit boards for providing accurately located and 
well defined openings for receiving the leads of electrical components is 
a well known art. Usually, the shank of the drills themselves may be of 
the order of 1/8 inch in diameter and are rotated at an extremely high 
speed by a motor driven holding spindle. Oftentimes a plurality of 
spindles are provided for holding a like plurality of drills so that 
simultaneous drilling of various holes in a number of circuit boards in 
side by side relationship can be carried out. 
Normally, the drill shanks are held in the spindles by jeweler type collets 
with set screws to assure concentricity and reliability in the proper 
gripping of the drill shank. Such collets are not only expensive, 
particularly where several are required in the case of multiple drill 
systems, but in addition the changing of drills can become somewhat time 
consuming in that the set screws must be loosened and then retightened 
with the new drill shank in position. 
In an effort to simplify the replacement of drills or the substitution of 
different drills in a spindle arrangement, it has been proposed to provide 
a centrifugal type holder for the drill shank wherein the drill structure 
can be very easily slipped into the spindle and then after starting the 
drill, centrifugal forces develop which result in a tight gripping of the 
drill. There is only one type of centrifugal holding arrangement of which 
we are aware and in this particular system, the drill is provided with a 
specially made cylinder of larger diameter than the drill shank in turn 
designed to fit within the spindle. Upper sections of this cylinder are 
free to move radially outwardly under centrifugal force such that they 
will frictionally engage the inside wall of the spindle bore receiving the 
cylinder and thus hold the drill to the spindle by centrifugal force under 
high speed rotation of the spindle. 
While the foregoing centrifugal system permits fairly rapid interchanging 
of drills, each drill must be provided with the specific type of cylinder 
for cooperation with the spindle and again a relatively high cost is 
involved. Moreover, problems have developed with this type of centrifugal 
system in assuring concentricity of the drill as well as dynamic balancing 
of the system generating the centrifugal forces. 
BRIEF DESCRIPTION OF THE PRESENT INVENTION 
With the foregoing considerations in mind, the present invention 
contemplates an improved centrifugal force holding technique particularly 
useful for holding and gripping drills used in drilling printed circuit 
boards which overcome some of the disadvantages associated with the one 
known system. More particularly, the arrangement of the present invention 
is such as to greatly reduce the cost of an appropriate holding means for 
the drill, and yet provide the advantage of easy replacement for 
interchange of drills and assure a high degree of concentricity during 
operation. 
Briefly, the foregoing is accomplished by providing a centrifugal system 
wherein a drill holding spindle is provided with radially contractable 
wall portions surrounding the shank of the drill received in the spindle. 
Centrifugal force generating means in the form of weights are coupled to 
the spindle for rotation therewith in a manner to exert contracting forces 
on the wall portions of the spindle so that the shank is gripped and held 
by the spindle by the generation of these centrifugal forces in response 
to rapid rotation of the spindle. 
The structure of the centrifugal force generating means is such as to 
assure proper dynamic balancing to thereby in turn assure uniform gripping 
of the shank to maintain proper concentricity. 
This invention also contemplates the provision of a positive engagement 
collar structure for use with larger sized drills in cooperation with the 
centrifugal arrangement wherein a positive engagement of the collar with 
appropriate flats on the drill spindle is provided to thus prevent any 
slippage under lower speed and higher torque conditions in the event the 
generated centrifugal forces are not sufficient.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring first to FIG. 1, there is shown a high speed drill system in 
accord with the present invention including a drill holding spindle 10 
arranged to be rotated at high speed as by a motor 11. The spindle 10 
includes an interior axial bore 12 opening at its lower end 13, the 
exterior wall of the spindle 10 being provided with a plurality of 
exterior flats 14 at equal circumferentially spaced points on its exterior 
wall. These flats are better seen in the perspective view of FIG. 6 and in 
the preferred embodiment constitute three in number circumferentially 
spaced at 120.degree.. 
As also indicated in both FIGS. 1 and 6, the spindle 10 includes a similar 
plurality of exterior slots 15 extending from equal circumferentially 
spaced points between the flats radially inwardly to intercept the bore 12 
and longitudinally along the spindle 10 from the one end 13 to points 
beyond the ends of the flats as shown. 
With the foregoing arrangement, the flats can be biased radially inwardly 
to effectively decrease the cross sectional area of the bore 12 adjacent 
to the one end 13. 
The centrifugal force generating means in accord with the present invention 
comprises a plurality of eccentric weight means 16, 17 and 18 surrounding 
the spindle 10 with their centers of mass at equally spaced radial 
distances from the axis A--A of the spindle. Further details of the 
eccentric weight means will be described shortly. 
Shown below the spindle 10 is the shank 19 of a typical printed circuit 
board drill 20. Drills in the class of 1/8 inch diameter and under are 
each provided with a spring metal or plastic collar 21 pressed onto the 
1/8 inch shank a set distance from the point of the drill to preset the 
depth of drilling by limiting the extent of the shank 19 received within 
the bore 12 of the spindle 10. 
In the arrangement illustrated in FIG. 1, the spindle 10 is designed to 
produce enough friction to prevent the drill shank 19 from falling out of 
the spindle before rotation of the spindle starts. When the spindle is 
started, the centrifugal force developed by the eccentric weight means 16, 
17 and 18 acts against the spindle flats to urge them radially inwardly 
and thus grip the drill shank and lock the same against rotational and 
longitudinal movement relative to the spindle. 
Referring now to the end view of FIG. 2 along with FIG. 1, it will be noted 
that each of the eccentric weight means 16, 17 and 18 is in the form of a 
series of lamination plates stacked in a direction parallel to the spindle 
axis having off-center openings 22 through which the spindle 10 passes. In 
FIG. 2, the bottom lamination plate of the eccentric weight means 16 is 
shown in full lines, the bottommost plate of the eccentric weight means 17 
having a portion thereof visible, the bottom lamination plate of the third 
series or set being indicated by the phantom lines 18. 
The off-center opening 23 of each of the lamination plates defines internal 
edge segments such as indicated at 23 and 24. These segments are straight 
and in opposing engaging relationship with at last one and in the 
embodiment illustrated two adjacent flats 14 of the spindle on the 
opposite side of the axis of the spindle from the center of mass of the 
lamination plate. In the view of FIG. 2, for the lamination plate 16, the 
center of mass will be directly to the left of the spindle axis as a 
consequence of the geometry of the plate. 
As also indicated in FIG. 2, the various series of lamination plates making 
up each of the eccentric weight means are provided with registering bores 
for receiving appropriate rivets which hold the assemblies together in 
interleaved fashion. One such rivet is shown at 25 for the series of 
plates 16. 
The interleaving of the three series of lamination plates will become 
clearer by reference to FIG. 3 wherein the lamination plates making up 
each of the series of eccentric weight means 16, 17 and 18 are shown 
schematically as elongated cross section rectangles. 
The respective plates in each of the series are held in given spaced 
relationship by appropriate washers 26 and it will be noted that by 
angulating each stack 120.degree. from the remaining stacks, the 
lamination plates can be interleaved so that their centers of mass are 
equally circumferentially distributed about the axis A--A of the spindle. 
Thus, as indicated in FIG. 3, each of the series of eccentric weights 16, 
17 and 18 includes an identical number of lamination plates, this number 
being six in the particular embodiment disclosed. Further, it will be 
evident from the arrangement of FIG. 3 that the centrifugal forces 
developed by each stack will be of equal magnitude and directed radially 
outwardly from the central axis of the spindle at angles 120.degree. to 
each other from the same axial point to provide dynamic balance. 
Referring specifically to FIG. 4 which shows a single lamination plate such 
as that incorporated in the eccentric weight means or stack 16, the 
centrifugal force developed by this lamination plate when rapidly rotated 
about the spindle axis A--A is indicated at F1. This centrifugal force 
will tend to move the lamination plate to the left when positioned as 
shown in FIG. 4 resulting in wedging engagement of the edge segments 23 
and 24 against the spindle flats 14 with forces indicated by the vectors 
F2 and F3. Because of the wedging action, the sum of the forces normal to 
the surfaces of the adjacent flats will actually be greater than the 
centrifugal force F1. As a consequence, there will be a large radial 
inward force on the flats of the drill spindle tending to contract the 
central bore 12 thereof and thus result in tight gripping of the drill 
shank. 
By providing the series of lamination plates making up each set of 
eccentric weight means, the centrifugal forces can be properly distributed 
in an axial direction along the drill spindle for proper gripping of the 
drill shank. Excellent concentricity of the drill is assured by this 
specific arrangement and it will be appreciated that the higher the speed 
of rotation, the greater will be the gripping force. 
FIG. 5 illustrates a typical one of the spacer washers 26 illustrated 
schematically in FIG. 3. 
Referring now to FIG. 6, further details of the specially designed drill 
spindle 10 will be evident. As shown, each of the flats 14 terminates at 
its lower end in a slightly raised flange or land 27. This land serves to 
hold the lamination plates in assembled relationship on the flats 14 when 
the same are assembled. Thus, the flats are radially contracted at the 
lower end 13 of the spindle 10 to permit the central openings in the 
lamination plates to ride over the lands, the spring bias of the exterior 
wall portions between the slots 15 returning the contracted wall flats to 
their normal position after all the lamination plates have been properly 
assembled in interleaved manner as described in conjunction with FIGS. 1 
and 3. 
In addition, the spindle 10 is preferably provided at its lower end 13, 
with further flats 28 below the lands 27. 
FIG. 7 illustrates the flats 28 and the purpose for these particular flats 
is to permit a positive engagement to be effected with a drill wherein a 
large diameter drill is used which runs at a lower rotational speed and 
requires greater torque. 
FIG. 8 shows in fragmentary perspective view such a drill including a shank 
portion 29 and larger diameter drill body 30. For these larger type 
drills, rather than the spacing collar 21 for the smaller drills 
illustrated in FIG. 1 there is substituted a collar 31 secured to the 
shank 29 as by a set screw and provided with three lugs 32 
circumferentially positioned such that they will engage the flats 28 when 
the shank 29 is received within the spindle 10 of FIG. 6. This coupling of 
the collar 31 to the flats 28 of the spindle will assure a positive lock 
of the drill shank against rotation relative to the spindle in those 
instances in which the centrifugal force developed does not provide 
sufficient gripping of the shank to overcome the applied torque. 
It will be understood that the shank 29 of the larger drills is of 
precisely the same diameter as the shank 19 of the smaller sized drills 
illustrated in FIG. 1 so that only a single spindle construction is 
necessary to accommodate both high speed and low speed drills of various 
sizes. 
OPERATION 
In operation, each drill spindle in the event multiple drill spindles are 
provided in a circuit board drilling operation has mounted thereon 
eccentric weight means as illustrated in FIG. 1, the respective series of 
lamination plates being interleaved all as described to provide for 
dynamic balancing. When the spindle 10 is stationary, the shank 19 of a 
drill can readily be manually inserted in the lower end of the bore 12 and 
the design of the spindle 10 and slots 15 is such that a slight inward 
biasing of the flats will frictionally grip the shank 19 and hold the 
drill in place. 
When the motor 11 of FIG. 1 is energized to rapidly rotate the spindle 10, 
the eccentric weight means made up of the three stacks of lamination 
plates will be thrown radially outwardly causing the edge segments of 
their internal openings to exert an inward radially directed biasing force 
on the flats of the spindle thereby gripping the shank 19 of the drill 
sufficiently to hold it during a drill operation. 
When the drill spindle motor is de-energized so that the spindle stops 
rotating, the drill can be easily removed by simple manually pulling 
downwardly on the same. 
Where low speed high torque larger diameter drills are used, the lugs 32 on 
the special collar 31 for the drill will engage the additional flats 28 at 
the lower end 30 of the spindle to provide a positive locking of the shank 
against rotation relative to the spindle. Again, when the spindle motor is 
energized and the spindle rotated at high speed, centrifugal forces will 
be generated to grip the shank and in cooperation with the locking collar 
assure that no slippage will occur. In this respect, the engaging inner 
flat surfaces of the lugs 32 are preferably at a very slight slope, the 
flats 28 at the end of the spindle similarly being sloped in an axial 
direction so that when the drill is fully inserted within the bore of the 
spindle, and clockwise torque is applied, the flats lock in dove-tail 
fashion to prevent the drill from pulling out as well as preventing 
further rotation. The action of the centrifugal force in gripping the 
shaft will further aid in preventing the drill from pulling out. 
As in the case of the smaller drills, when the motor is de-energized, the 
larger drill can readily be removed by simply rotating slightly 
counterclockwise to unseat the lugs from the additional flats and then 
pulling downwardly thereon. 
Since each of the lamination plates in each of the series or stacks of 
eccentric weight means are identically constructed; that is, of precisely 
the same geometry, the entire assembly can be provided with minimal costs 
as compared to prior art drill holding arrangements. 
The present invention thus provides a low cost drill holding system for 
high speed drills wherein interchanging or replacement of drills can be 
very easily carried out and wherein the drill shank itself is gripped with 
uniform dynamically balanced forces to maintain proper concentricity.