This invention pertains to a self-synchronizing and self-adjusting
tap driver for rigid tapping.
BACKGROUND OF THE INVENTION
In machining metallic work pieces, an apparatus called
a tap is used to create internally threaded holes for receiving screws in the metallic
The tap itself is a tool with external cutting threads.
In order to create the internally threaded hole in the work piece, the tap is rotated
and driven into the work piece to the desired hole depth, and then reverse rotated
and retracted from the work piece.
The tap is held by a tap driver, and the tap driver is
held or secured within a machine which provides the forward and reverse rotation
as well as the forward and reverse drive.
In creating the internally threaded hole, the tap driver
is first rotated and driven into the base material or metal to the desired depth.
Once the tap reaches the desired depth, the rotation of the tap driver and the tap
is reversed and the tap is retracted from the base material.
In order to create the best internally threaded hole, the
tap should be simultaneously advanced and rotated at precisely correlated rates
of rotation and forward movement for a given tap pitch. By way of example, a one-quarter-twenty
tap should be advanced into the work piece one inch for every twenty revolutions,
on 1,27mm [0.5 inch] for each revolution. In typical rigid tapping, the driver machines
provide the synchronization of the spindle rotation and feed advance to match the
During the creation of a tap hole, the machine spindle
goes through several stages, namely driving the rotating tap into the tap hole,
slowing the forward drive or feed rate and the rotation until the tap comes to a
stop in the work piece, reversing the direction of the rotation and accelerating
or increasing the reverse rate of rotation to match the desired tap pitch as the
tap is retracted.
It is appreciated by those of ordinary skill in the art
that during the changes in rotation speed, the feed advance of the tap must be adjusted
or correlated to precisely match the tap pitch. However, in practice it is very
difficult to precisely match the rotation, drive and tap pitch and there are small
errors that occur in the synchronization of the rotation speed and the feed rate
during the deceleration or slowing down phase, and during the reverse rotation acceleration
In typical prior art, tapping drivers are generally solid
in that they have no real ability to compensate for discrepancies between the feed
of the tap and the feed advance of the machine, but instead merely directly transfer
the rotation and drive of the tapping machine.
With solid tap holders, even very small errors in the synchronization
will apply a significant axial force on the tap, creating premature wear to the
tap and negatively affecting the thread quality produced by the tap.
In machining numerous internally threaded apertures, one
machine may be used to drill pilot holes into which the taps are driven, while a
different machine may be used for the actual tapping. This may lead to slight positioning
errors wherein the tap for instance is not exactly aligned with the pilot hole,
but instead may be one or two thousandths of an inch off.
It will be appreciated by those of ordinary skill in the
art that there is a need for a tap driver which has some limited flexure for the
location errors associated with locating the tap with respect to the desired tap
Known tapping devices are described in
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are described below
with reference to the accompanying drawings, which are briefly described below.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
- Figure 1
- is an elevation view of an embodiment of this invention showing a tap driver
with a tap device therein;
- Figure 2
- is an elevation cross-sectional view of an embodiment of this invention showing
a tap driver with a flexible area machined with helical coils between the shank
portion and the chuck portion;
- Figure 3
- is an elevation view of a tap driver body which may be used in an embodiment
of this invention;
- Figure 4
- is an elevation cross-sectional view of the embodiment of the invention shown
in Figure 1 but illustrating the compression flexure of the central portion of the
tap driver body;
- Figure 5
- is a top cross-sectional view of the embodiment of the invention shown in Figure
- Figure 6
- is an elevation view of an embodiment of the invention, illustrating lateral
flexure provided by an embodiment of this invention;
- Figure 7
- is an elevation view of another embodiment of a tap driver body which may be
used in connection with this invention; and
- Figure 8
- is an elevation partial view of another embodiment of a tap driver body which
may be used in an embodiment of this invention.
Many of the fastening, connection, manufacturing and other
means and components utilized in this invention are widely known and used in the
field of the invention described, and their exact nature or type is not necessary
for an understanding and use of the invention by a person skilled in the art or
science; therefore, they will not be discussed in significant detail. Furthermore,
the various components shown or described herein for any specific application of
this invention can be varied or altered as anticipated by this invention and the
practice of a specific application or embodiment of any element may already be widely
known or used in the art or by persons skilled in the art or science; therefore,
each will not be discussed in significant detail.
The terms "a", "an", and "the" as used in the claims herein
are used in conformance with long-standing claim drafting practice and not in a
limiting way. Unless specifically set forth herein, the terms "a", "an", and "the"
are not limited to one of such elements, but instead mean "at least one".
The tap driver provided by this invention may be used in
combination with any one of a different machines or applications, with no one in
particular being required to practice this invention. It may be used for instance
in combination with a machining center which has rigid tapping capability.
Figure 1 is an elevation view of an embodiment of this
invention showing a tap driver attachment with a tap device therein, illustrating
tapping attachment 1, tap driver body 2, shank portion 2a of tap driver body 2,
chuck portion 2c of tap driver body 2, tap 40, collet nut 3, tap body sleeve 4,
and shank flat 30 to attach to a machine spindle or into another shank which fits
into a machine spindle. The shank flat 30 facilitates the securement of the tap
driver to its source of rotation or ultimately to the machine spindle.
Figure 2 is a cross-sectional elevation view of an embodiment
of this invention which shows the tapping attachment 1, tap driver body 2, with
tap driver body shank portion 2a, tap driver body central portion 2b, and tap driver
body chuck section 2c. In the central portion 2b of the tap driver body 2, helical
coils 5 have been cut into the body around the circumference to provide a spring
or tension and compression properties (and limited lateral flexure) different or
dissimilar from that in the shank portion 2a and chuck portion 2c.
The helical coils can be precisely cut to provide the desired
flexure, tension and compression necessary to allow the attachment body to self
synchronize to forces imparted on the tap during tapping. Compression occurs by
an upward force on the guide bushing 8 contained within tap driver body axial aperture
11. When an excess force is incurred, it will be transmitted through guide bushing
8 to first drive pin 6. First drive pin 6 then imparts or transfers said axial force
to the helical coils 5 in central portion 2b to cause compression of the central
portion 2b of the tap driver body 2.
Compression gaps 17 provide space for, and limit, the movement
of guide bushing 8 during compression of center portion 2b. Compression gaps 17
are shown larger than they actually would be for illustrative purposes only. In
a typical tapping attachment, the compression gaps may only need to be one-half
(S) of a millimeter in order to provide the sufficient movement for the desired
The helical coils 5 may be cut into tap driver body 2 accurately
and precisely to create the desired spring characteristics to equate the central
portion 2b of tap driver body 2 to a 16.61 kg (30 pound) spring. The helical coils
5 may be machined into the central body portion by Helical Products, Inc. The extension
and compression rate is approximately 208.27 kg per cm (1167 pounds per inch) reference,
the spring extension and compression 0.079 cm (thirty one-thousandths inch) maximum
with a reaction force of 15.88 kg (85 pounds), plus or minus ten percent. The preferred
permitted lateral translation of spring is 0.0076cm (three one- thousandths of an
inch). The preferred material out of which the spring and/or tap driver body is
constructed, is generally known as C300 metal.
One embodiment of this tapping attachment is able to provide
some slight lateral movement of the tap to the hole while still providing a sufficiently
accurate tap hole. The preferred embodiment of the invention, through the helical
groove portion, provides approximately 0.0051 cm (2/1000 of an inch) of movement
side to side at the end of the tap to allow for slight mis-alignment of the tap
with the hole.
In a typical tapping application, the helical grooved area
may provide for axial movement of up to 0.079 cm (31/1000 of an inch), even though
the typical axial movement will only be in the 0.0051 cm (2/1000 of an inch) to
0.013 cm (5/1000 of an inch) range. It is preferred that there be approximately
0.079 cm (31/1000 of an inch) movement in response to approximately 16.61 kg (30
pounds) of axial force, although the predetermined movement may be in response to
any range of predetermined forces, all within the contemplation of this invention.
Although there are embodiments of this invention in which
are not one piece or integral, it is preferred that the compression/tension area
be integral or one piece with the tap driver body for concentricity and other reasons.
Utilizing an embodiment of this invention wherein the tap driver body is one piece
removes the reliance on the accurate assembly or fitting of two pieces together.
Figure 2 further illustrates tap driver body axial aperture
11 through which cutting fluid or lubricant may be provided or routed for the tapping
procedure. The guide bushing axial aperture 10 further provides the necessary conduit
for the coolant to reach the collet chuck 12 and be provided to the tap hole during
tapping, in accordance with known means by those of ordinary skill in the industry.
Figure 2 further illustrates second drive pin 9 spaced
apart from tap driver body 2 at least a distance equal to compression gap 17 to
allow its movement. The first end 9a of second drive pin 9 is in the at least one
drive pin aperture in the outer surface of the guide bushing 8 and a second end
9b of second drive pin 9 fits within aperture 20, which is better shown in Figure
3 and is preferably oval shaped. Ball bearings 7 are provided in gaps above and
below the helical coils 5 to maintain the first drive pin 6 and the second drive
pin 9 in their respective locations, while still allowing relative axial and lateral
movement. The first end 6a of first drive pin 6 is in the at least one drive pin
aperture in the outer surface of the guide bushing 8 and a second end 6b of first
drive pin 6 is in the at least one drive pin aperture 21 (better shown in Figure
5) in the inner surface of the tap driver body 2.
O-rings 16 are shown between guide bushing 8 and tap driver
body 2, the O-rings 16 providing a seal for containment and control of coolant injected
into tap driver body axial aperture 11.
The tapping attachment further includes tap body sleeve
4 which generally surrounds the central portion 2b of tap driver body 2. Figure
2 further shows collet nut 3 around the chuck portion 2c of tap driver body 2 for
securing the tap into the chuck collet area 12. Also shown in Figure 2 is shank
flat 30 in the shank portion 2a of tap driver body 2, and tap 40. Figure 2 further
shows sliding ring 33 and tap square 34.
The term central portion as used herein in reference to
the tap driver body is meant to include any area or portion of the tapping attachment
between where the tap driver is held by the tapping machine, and where the tap is
held by the tap driver.
Figure 3 is an elevation view of the tap driver body 2,
illustrating the shank portion 2a, central portion 2b and chuck portion 2c. Helical
coils 5 are shown cut into central portion 2b and surrounded by first drive pin
aperture 21 and second drive pin aperture 20. It will be noted that first drive
pin aperture 21 provides a tight fit for first drive pin 6 to provide little or
no relative movement between first drive pin 6 and tap driver body 2. On the other
hand, second drive pin aperture 20 is intentionally larger than second drive pin
9 to allow for some relative movement, as is more fully illustrated in Figure 2.
Collet nut 3 is also shown around the chuck portion 2c of tap driver body 2.
Figure 4 is the same embodiment of the invention and view
as shown in Figure 2, with each item and element being identically numbered. Figure
4 illustrates the axial or compression movement in the central portion 2b of the
tap driver body 2 when forces are exerted on the tap driver body 2. Figure 4 shows
the helical portion being compressed and the compression gap 17 being fully closed
(there is no gap in Figure 4 as compared to Figure 2).
Figure 5 is a top cross-sectional view of a tapping attachment
1 contemplated in one embodiment of the invention, illustrating three first drive
pins 6 as preferably offset one hundred twenty degrees from one another, ball bearings
7, central portion 2b of tapping attachment 2, tap body sleeve 4, guide bushing
8 and guide bushing axial aperture 10.
It will be appreciated by those of ordinary skill in the
art that variations of three drive pins 6 and spacing or offsetting between drive
pins 6 may be varied into any one of a number of different configurations and actual
numbers of drive pins 6, all within the contemplation of this invention.
Figure 6 is an elevation view of a tapping attachment 1
contemplated in one embodiment of the invention, and illustrates lateral flexure
provided by an embodiment of this invention.
Figure 6 shows tapping attachment 1, tap driver body 2,
shank portion 2a of tap driver body 2, chuck portion 2c of tap driver body 2, tap
40, collet nut 3, tap body sleeve 4, and shank flat 30.
Figure 6 further illustrates a slight lateral movement
of the lower end of the tap 70, by a distance 71. The lateral movement of the lower
end of tap 70 is generally provided by the central portion 2c of the tap driver
body 2 and the grooves provided therein.
Distance 71 in Figure 6 is exaggerated for illustration
purposes, but generally may be 0.0026 or 0.0051 cm (1 or 2 one-thousandths of an
inch), which is generally an acceptable tolerance when machining tap holes. There
may be a number of reasons this lateral flexure is needed. One example is if one
machine is used to drill the tap start holes and a second machine is used to actually
tap the whole, there may be some slight variances in the relative location of the
intended drill holes versus tap hole.
Figure 7 is an elevation view of another embodiment of
a tap driver body 2 which may be used in connection with this invention, illustrating
a honeycomb area 79 which provides the predetermined compression and tension for
absorbing and providing axial forces, and which would also provide for a lateral
flexure. The honeycomb or matrix configuration includes a plurality of first framework
segments 80 and a plurality of second framework segments 81. The matrix area 79
may be calibrated to provide the desired predetermined axial compression and tension,
as well as the predetermined lateral flexure.
Figure 8 is an elevation partial view of a tap driver body
2, a shank portion 2a, and a shank flat 30. Figure 8 illustrates another embodiment
of this invention which provides the axial tension and compression, along with some
Figure 8 illustrates a dual flange area separated by a
structure which provides the predetermined compression and tension for absorbing
and providing the axial forces. First flange 74 is attached to shank portion 2a
of the tap driver body 2, and second flange 73 is attached to the chuck portion
of the tap driver body 2, with O-ring 75 sandwiched between the two. Tension pegs
76 provide rotational stability between the flanges and are attached to the first
flange 74 and to the second flange 73. The tension pegs 76 have a predetermined
spring tension factor which provides the desired axial tension flexure and the o-ring
75 provides the desired axial compression flexure. Any number of tension pegs 76
may be used within the contemplation of the invention.
An embodiment of the invention therefore comprises a tap
driver for rigid tapping, with a tap driver body comprising: a shank portion at
a first end of the tap driver body, the shank portion configured to be secured to
a tapping machine; a chuck portion at a second end of the tap driver; and a central
body portion between the shank portion and the chuck portion, the central body portion
having a predetermined axial compressibility in response to axial forces imparted
on the tap driver during tapping.
In another embodiment of the invention, the central body
portion between the shank portion and the chuck portion includes helical spring
coils, the helical spring coils having a pre-determined compressibility for absorbing
In yet another embodiment of the invention, the helical
coils have a predetermined axial tension which allows a predetermined amount of
expansion in response to axial tension forces imparted on the tap driver during
tapping, in combination with the predetermined compressibility and alone. In a further
embodiment of the invention, the helical coils provide a predetermined lateral flexure
in response to lateral forces imparted on the tap driver during tapping, to allow
the tap itself to adapt or move slightly in the lateral direction, to create a tap
In a process embodiment of the invention, a process for
making a tap driver body for rigid tapping is provided, the process generally comprising
the steps of providing a tap driver body comprising, the tap driver body comprising:
a shank portion at a first end of the tap driver body, the shank portion configured
to be secured to a tapping machine; a chuck portion at a second end of the tap driver;
and a central body portion between the shank portion and the chuck portion; and
machining a helical coil into the central body portion, the helical coil having
a predetermined compressibility or expandibility.
During the tapping procedure, as the tap is driven into
or out of the base material, typically metal, additional forces are placed on the
tap which places the tap out of the desired synchronization. The central portion
of the tap driver provided by this invention provides a compressibility and an expansion
factor, which help compensate for these forces and provides the desired synchronization
in tension and in compression.
It is to be understood that the invention is not limited
to the specific features shown and described, since the means herein disclosed comprise
preferred forms of putting the invention into effect.