BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a self-reversing tapping attachment
according to the preamble of claim 1 and as known from US-A-3037393.
The field of the invention is that of driver elements in self-reversing
tapping attachments, which are tools that carry taps for threading holes and are
driven by an external drive source such as a driving machine, drive being imparted
from a movable body in the tapping attachment body to a member carrying the tap
and the tapping attachment including means for reversing the rotation of the tap.
2. Description of the Prior Art
Related patents to the same inventor as named on the application
herein are U.S. Patent Nos. 3,397,588; 3,472,347; 3,717,892; 3,946,844; 3,999,642;
4,014,421; 4,029,429; 4,067,424; and 5,011,344.
The above-cited patents relate, among other things, to clutching arrangements in
tapping attachments, both for direct drive and for reverse drive.
Existing tapping attachments are many and varied, and constitute
a relatively mature art. Within the relatively recent past, however, there has
arisen a need for improvements in tapping attachments due to the advent of high
speed tapping that is, tapping at high rpm. A need for improvement in tapping attachments
for high speed application is particularly pronounced with respect to self-reversing
tapping attachments, i. e., tapping attachments which provide for
a reverse rotation of the tap in order to aid its withdrawal from a hole which
has been threaded by it.
A common device for imparting drive to a drive member of a tapping
attachment in existing devices is the ball drive. In a ball drive, a driver member
impacts with driver balls held in or associated with a driving element which in
turn impacts with a dog or like member for the purpose of imparting drive, either
forward or reverse, to a tap holder in the form of a spindle.
In existing ball drive arrangements, particularly in high speed applications,
impacts between the balls and the various dogs and splines with which they engage
for the purpose of imparting drive, result in shock and vibration, together with
substantial wear of the machine elements.
The above mentioned document US-A-3037393 discloses a self-reversing
tapping attachment comprising drive means connectable to a source of rotational
drive. The attachment comprises a driving component, a driven component, torque
transmitting members for transmitting direct drive between said components including
coupling members, and torque transmitting members for transmitting drive in reversed
direction between said components including a reversed drive members operatively
connectable with said driven component to rotate m the direction opposite that
of the driving component, one of said coupling members being axially shiftable
relatively to said components from a first position engaging the driving component
to transmit torque between said components in direct drive relation to a second
position engaging one of said reversed drive members to transmit torque between
said components in reversed drive relation, said shiftable coupling member being
adapted to be retained positively in either of its positions until a resilient
member acting on said coupling member due to a displacement of said components
relative one another has accumulated a force great enough to cause said coupling
member to shift in a snapping movement to the other position.
The need for drive elements of tapping attachments able to withstand
high performance conditions is particularly pronounced in regard to Computer Numeric
Control (CNC) applications. Under CNC operation, time is particularly of the essence
for withdrawing a tap from a hole which it has threaded in that the CNC operation
provides for a computer controlled transfer of driving force from one tap attachment
to another, timely removal of a previously used tap from a hole being critical
in such an operation.
Therefore, there has been a felt but unfulfilled need for a driving
arrangement in a tapping attachment whereby in a ball drive, shock and wear within
the driving and clutching elements are minimized, in particular for high speed
SUMMARY OF THE INVENTION
The present invention is defined in the appended claims.
In a self-reversing tapping attachment, an improvement is provided
comprising drive means connectable to a source of rotational drive and a drive
transmitting means engagable with the drive means and including at least one driving
ball member, the drive transmitting means defining at least one slot for the at
least one ball member, the slot including a ramp section inclined such that on
engagement between the drive means and the at least one ball member, the latter
travels upwardly, whereby impact between the driving means and the drive transmitting
means is cushioned. A radially extending member on a tap holder member may have
a radius of curvature less than the radius of curvature of contact members on the
drive transmitting means.
BRIEF DESCRIPTION OF THE DRAWINGS
DESCRIPTION OF A PREFERRED FORM OF THE INVENTION AND PREFERRED METHOD
- Fig. 1 is a side view somewhat simplified, of a tapping attachment in accordance
with the invention being driven by a driving machine;
- Fig. 2 is a cross-sectional view, somewhat simplified of a tapping attachment
including a preferred form of the invention;
- Fig. 3 is a cross-sectional view, along the line A-A, depicting a driving arrangement
in accordance with the invention;
- Fig. 4 is a detail view of a driving arrangement in accordance with the invention;
- Fig. 5 is a side view of a part of a driving arrangement in accordance with
As depicted in Fig. 1, a tapping attachment 10 is connected to a
source of rotational drive in the form of a driving machine 12. A holding stem
14 (shown fragmentarily only) is at a side of the housing 16 of the tapping attachment
10 and is connectable in conventional fashion to the driving machine 12 to form
a restraint preventing rotation of the housing 16 of tapping attachment 10.
A spindle member 18 extends outwardly of housing 16. At its upper
end, spindle member 18 extends to driving machine 12. At the lower end of spindle
member 18 a tap 20 is attached, the tap 20 being threaded so as to make threaded
holes in work pieces (not shown) and including a central bore (not shown).
Whereas the housing 16 is held stationary against rotation, a movable
component 22 of tapping attachment 10 is connectable to driving machine 12 to be
rotatable to provide drive to the tap 20, as described more fully hereinbelow.
Referring now to Figs. 2-5, inclusive, the moveable part 22 of tapping
attachment 10 defines a central bore 24, with the spindle member 18 therein. An
insert 29 containing a conduit 26 is contained within central bore 24, and around
the periphery of the conduit 26 at a lower portion thereof is disposed a resilient
sleeve 27. Insert 26 forms a conduit for passage of coolant therethrough and through
tap 20 for the purpose of cooling the tap and clearing debris in the form of cuttings
and the like from the work piece. Resilient sleeve 26 is provided for the purpose
of affording the capability of axial movement of the conduit 26 in connection with
axial movement of movable member 22 on the occasion of a shift between forward
and reverse drives as described in more detail hereinbelow.
Within housing 16 is a forward drive member 30, of generally annular
configuration defining a central bore 38 and fitting within housing 16. Forward
drive member 30 carries on its radially inward wall at least one forward drive
spline member 36. Forward drive spline member 36 is connected with a neutral area
shoulder 37 located axially downwardly thereof (i. e., toward the
lower end of the spindle member 18 where the tap 20 is held).
Positioned radially inwardly from forward drive member 30 in the
depicted forward drive configuration is drive transmitting means in the form of
a drive sleeve member 40. Drive sleeve member 40 has generally annular configuration
defining a central bore 42. Extending radially inwardly from the peripheral inner
wall of member 40 is an inner drive spline member 44. Driver sleeve member 40
defines at its periphery at least two slots 46, 48 for accommodation and movement
therein of drive balls 32, 33, respectively. In the forward drive mode depicted
forward drive member spline 36 is engaged with ball member 32.
Slots 46, 48, respectively, are of generally ellipsoidal configuration.
Stated in other terms, slots 46, 48 may be described alternatively as rhomboidal
quadrilaterals having opposite sides generally parallel but instead of vertices
with acute and oblique angles, with ends where the vertices would be, being of
arcuate configuration. A first ramp member 50 and a second ramp member 52 constitute
inclined sides of the lower part of slot 46. Under the depicted configuration of
slot 46, the opposite side to the side which comprises ramp 50 is generally parallel
to ramp 50 and is designated by the reference numeral 54. Similarly, the side opposite
to the side constituting ramp 52 is generally parallel thereto and is designated
by reference numeral 56.
Also disposed within housing 16 is reverse drive member 58. At the
upper inner periphery of reverse drive member 58 is defined a neutral region in
the form of a shoulder 60. Connected to neutral region 60 is reverse drive spline
member 62 disposed axially downwardly from neutral region 60. Reverse drive member
58 defines a central bore designated as 64, and has a generally annular configuration.
Inner drive sleeve spline 44 on driver sleeve 40 comprises a generally
arcuate contact area 66. Connected to contact area 66 is a generally arcuate intermediate
region 68, and connected thereto is a second contact surface 70 configured in
the same manner as the first contact surface 66. The interior of drive sleeve spline
44 with the radially inward wall of drive spline 44 and the drive spindle disposed
adjacent thereto, in effect, constitute two slots 72,74.
Carried on drive spindle member 18 in a slot 76 defined therein and
intermediately thereof along the axial extent is at least one drive pin 78. Pin
78 is generally cylindrical in configuration with a substantially circular cross-section.
In accordance with an optional feature of the invention, the radii of curvature
of the contact surfaces 66,70 of inside drive spline 44 are larger than the radius
of curvature of drive pin 78. In particular applications, such radii of curvature
of the contact surfaces 66,70 may exceed the radius of curvature of drive pin
78 by 10-25%.
Spindle member 18 has an enlarged section 80 at its lower end. Defined
at the lower end 80 of spindle 18 are threaded screw holes 82,84. In screw holes
82,84 are screw members 86,88, the ends of which fit into sockets in the sidewalls
of a tap holder 90 (shown fragmentarily only), whereby the latter is held in position
relative to spindle member 18.
A quick change mechanism 92 is disposed at the end of tap holder
90 and enables ready change from one tap to another (not shown). Quick change mechanism
92 includes a ring member 94 with contained coil spring member 96.
In the sidewall of tap holder 90 near the end thereof are oppositely
disposed bores 98,100, for radial pins 102,104 held in position by ring member
In operation, rotation is transmitted from the driving machine 12
to the forward drive member 32 and the reverse drive member 58, which are connected
to movable member 22 by conventional means (not shown) in the tapping attachment
10, reverse drive member 58 being also connected through conventional gearing (not
shown), such as is disclosed in co-pending application 07/330,752 filed March
30, 1989 and related continuation-in part application Serial No. 07/715,343 filed
June 14, 1991 to the same inventor as the instant application and incorporated
by reference herein.
In forward drive, the forward drive spline 36 on forward drive member
32 engages with balls 32, 33 of driving sleeve 40 as depicted in Fig. 3. Such engagement
comprises in effect a collision between the spline 36 and the balls 32, 33. In
accordance with the invention, and as a result of the ellipsoidal shape of slots
46, 48, the driving balls 32, 33 experience less shock and wear than in existing
devices. Upon impact, the driving balls 32, 33 are urged up the ramp structures
50, 52, thereby providing a buffered or cushioned impact between the spline 36
and the balls 32, 33. Due to the configuration of the slot 46, impact in either
direction is accommodated in the described manner.
Upon engagement of the drive spline 36 with balls 32, 33 as described
above, drive sleeve 40 is urged in the forward rotational direction and as a result,
inner drive spline 44 is urged toward drive pins 78 on drive spindle 18. Due to
the greater radius of curvature of the engagement surfaces 66, 70 of the drive
sleeve 40 as opposed to the radii of curvature of drive pins 78, the impact between
inner drive spline 44 and its contact surface at 66, 70 with drive pin 78 is less
abrupt and sharp than in the case where the radii of curvature were the same. In
addition contact between surfaces 66, 70 and pins 78 is linear as opposed to point
contact, thus distributing the impact and reducing shock and wear. Therefore, excessive
shock and wear on the drive spline 44 of the drive sleeve 40 as well as on the
drive pins 78, are avoided.
Coolant is provided during tapping from the driving machine 12 via
the conduit 26. When the hole has been threaded to the selected depth and the tap
is to be withdrawn from the hole, the tapping attachment 10 is raised by the driving
machine 12. At this point, the tap is embedded in the hole and removal is most
conveniently accomplished by reversing the tap rotation.
Accordingly when the tapping attachment is raised the spindle 18
and tap 20 remain in the hole, the forward drive member 32 and reverse drive member
58 moving axially upwardly relative to the spindle member 18 and tap 20.
As a result of the aforesaid axially upward movement balls 32,33
travel along the neutral range shoulders 37, 60 until the reverse drive member
58 and rear drive spline 64 engage balls 32,33 in driving engagement, thereby
causing reverse rotation of the spindle 18 and tap 20, enabling efficient withdrawal
of the tap 20 from the hole. As in forward drive, driving engagement is cushioned
due to the configuration of slots 46, 48, the cylindrical shape of drive pins
78, and the greater radii of curvature of contact member 66, 70 vis a vis the radii
of curvature of drive pins 78.
Therefore, there have been described ball drive tapping attachments
which provide for driving engagement with reduced shock and wear to driving parts
thereby increasing efficiency and longevity.