Thread reconditioning tool

A tool for reconditioning or restoring the threads of externally threaded members, such as bolts, studs, and the like, includes, in one embodiment, a collet having a bore formed therethrough with a portion of the bore defining a guide surface, and a threading insert that includes thread cutting means. In order to recondition threads, the threading insert is selectively positioned along the longitudinal axis of the threaded member with the thread cutting means engaging the threads of the member. The collet is placed over the end of the member and positioned such that the threading insert is received within a socket formed in the collet thereby retaining the threading insert in place against the externally threaded member. Rotation of the tool relative to the threaded member causes the cutting means to recondition the threads. In one alternate embodiment, the cutting means are associated with the collet rather than with the threading insert.

FIELD OF THE INVENTION 
The present invention relates to threading tools and, more particularly, to 
tools for reconditioning or restoring the threads of externally threaded 
members. 
BACKGROUND OF THE INVENTION 
Threaded members frequently become unusuable because of damage to the 
threads and/or the presence of foreign matter between the threads. Thread 
damage includes both physical damage to the thread profiles and damage to 
the surfaces of the threads. Thread profile damage can be caused when the 
threaded member is mis-threaded, cross-threaded, stripped, or otherwise 
abused; and surface damage can occur through long continued use of the 
threaded member which causes surface spalling of the threads. Foreign 
matter, such as corrosion, rust, paint, and the like, can be formed or 
introduced between the threads by leaving the threaded member unprotected 
from the environment or the source of foreign matter. In general, such 
threaded members can be reconditioned or restored by means of a thread 
reconditioning tool. 
A wide variety of thread reconditioning tools are known, and they can 
generally be divided into threading dies, either one piece or multi-piece 
dies, and adjustable thread reconditioning tools. Single piece threading 
dies, which are primarily used to cut threads into unthreaded shafts, can 
also be used to recondition threads. Typically, the die is started at one 
end of the threaded member and rotated relative the threaded member until 
the cutting edges of the die restores the original thread profile, reforms 
the surface of the threads, and removes any foreign matter from between 
the threads. Multi-part threading dies, which generally have two 
diametrically opposite cutting die portions, are similar in operation to a 
single piece dies except that they can be assembled to the threaded member 
anywhere along the longitudinal axis of the member. Adjustable thread 
reconditioning tools generally include a guide surface, such as a curved 
or `V` shaped anvil against which the threaded member is placed, and a 
radially adjustable thread cutting means which is manually adjusted to 
engage the thread. 
Each one of the known thread reconditioning tools is adequate to perform 
its intended function, but each possesses one or more drawbacks inherent 
in its design. For example, the single piece threading die must be started 
over the end of the theaded member. This is particularly disadvantageous 
when only the middle portion of a relatively long threaded member is 
damaged or when the end-most threads are damaged making it difficult to 
properly start the die. While multi-part dies can be assembled onto the 
threaded member at the desired longitudinal location, they require an 
adjusting step to position the die portions relative to one another and to 
the threaded member. Likewise, the adjustable thread reconditioning tools 
also require an adjustment step to locate the thread cutting means 
relative to the threaded member. The adjustment step required by 
multi-part dies and adjustable thread reconditioning tools requires that 
the tool user have a minimum level of skill to properly adjust the cutting 
means with respect to the thread to be reconditioned. For example, if the 
cutting means is loosely adjusted, the thread may not be reconditioned on 
the first attempt, thereby requiring repeated efforts to successfully 
recondition the thread. Moreover, if the cutting means is too tight, the 
final reconditioned thread may be smaller in diameter than acceptable. 
Therefore, it is a broad overall object of the present invention, among 
others, to provide a new and improved thread reconditioning or restoring 
tool which overcomes the disadvantages of known thread reconditioning 
tools. 
Accordingly, it is an object of the present invention to provide a thread 
reconditioning tool for reconditioning or restoring damaged threads and/or 
removing foreign matter from between threads on a threaded member which is 
simple in construction, has a minimum number of parts, is simple to 
operate, and inexpensive to manufacture. 
It is another object of the present invention to provide a thread 
reconditioning tool which can be quickly placed over and located at a 
selected position along the longitudinal axis of a threaded member. 
It is still another object of the present invention to provide a thread 
reconditioning tool which can be quickly and conveniently engaged and 
disengaged with the threads of an externally threaded member by a tool 
user having a minimum level of skill. 
It is a further object of the present invention to provide a thread 
reconditioning tool which can be quickly and conveniently operatively 
engaged with threads of a threaded member without making any adjustments 
of the cutting means relative to the thread. 
SUMMARY OF THE INVENTION 
In accordance with the aforementioned objects, the present invention 
provides a thread reconditioning tool for reconditioning or restoring 
damaged threads and/or removing foreign matter from between the threads of 
an externally threaded member which includes, in one embodiment, a collet 
having a throughbore and adapted to be placed over and selectively 
positioned along the longitudinal axis of the threaded member with a 
portion of the collet functioning as a guide surface, a threading insert 
having a thread cutting means on an inner surface thereof, and an insert 
retaining means associated with the collet to retain the cutting means of 
the insert against the threads of the threaded member, whereby rotation of 
the collet and the retained threading insert will cause the cutting means 
to recondition the threads. In another embodiment of the present 
invention, the cutting means are associated with the collet and the guide 
surface is associated with a retainer.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of a thread reconditioning tool in accordance with 
the present invention is shown in FIGS. 1 and 2 and includes a collet 10 
and a threading insert 12 which are both adapted to be assembled together 
as shown in FIG. 3 to form the thread reconditioning tool. 
The collet 12 is formed as a hexagonal element with a plurality of flat 
sides 14 disposed about a central axis 16. The collet 12 has an opening or 
bore 18 formed therethrough and a cavity or a socket 20 which is adapted 
to receive the threading insert 12, as described in detail below. The 
inside diameter of the bore 18 is preferably equal to the major diameter 
of the thread to be reconditioned and a selected clearance dimension. The 
socket 20, in its preferred form, has a semi-annular configuration which 
is defined by a peripheral locating surface 22, two flats 23 and 24, and a 
bottom surface 25. The smooth inside diameter of the bore 18 opposite from 
the socket 20 constitutes a guide surface 26 the function of which is 
described in detail below. 
The threading insert 12, which has a semi-cylindrical configuration as 
shown in FIG. 12, is formed about a central axis 28 and is defined between 
an outside diameter surface 30, two diametric flats 31 and 32, and an 
inside diameter surface 34. The outside diameter surface and flats, 30-32, 
of the threading insert 12 and the peripheral locating surface and flats, 
22-24, of the collet 12 constitute surfaces which are adapted to cooperate 
with one another to retain the threading insert 12 in the socket 20 during 
thread reconditioning as described below. 
Thread cutting means, generally designated by the reference character 36, 
are located on the inside diameter surface 34 of the threading insert 12 
and include, in the preferred form, two sets of thread cutters that are 
separated from one another by a relief cutout or flute as is well known in 
the art. 
The threading insert 12 and the collet 10 are adapted to be assembled 
together as shown in FIG. 3 with the outer diameter locating surface and 
the flats, 30-32, of the threading insert 12 abutting the corresponding 
locating diameter surface and flats, 22-24, of the collet 10 such that the 
threading insert 12 is retained within the collet 10 with the cutting 
means 36 maintained in a fixed, spaced relationship relative the guide 
surface 26. The respective dimensions of the threading insert 12 and the 
socket 20 are selected such that a sliding fit exists between the 
threading insert 12 and the socket 20 to permit convenient insertion and 
removal of the threading insert 12 from the socket 20. With the collet 10 
and the insert 12 assembled as described, the guide surface 26 is adapted 
to contact the tips or distal ends of the threads on the shaft to be 
reconditioned and thereby retain the shaft in engagement with the cutting 
means 36 on the threading insert 12. The physical relationship of the 
cutting means 36 relative to the locating surfaces is chosen such that the 
cutting means will effect the desired reconditioning of the threads when 
the reconditioning tool is assembled to a threaded shaft as described 
below. 
A threaded shaft 38 may be reconditioned using the reconditioning tool as 
shown in FIGS. 4 and 5 by placing the threading insert 12 onto the shaft 
38 adjacent the portion of the threads --X-- to be reconditioned. The 
collet 10, with its socket 20 facing the threading insert 12, is placed 
over the end of the threaded shaft 38 and moved toward the insert 12 until 
the insert is received in its socket 20. As shown in FIG. 5, the insert 12 
and the collet 10 are retained on the threaded shaft 38 with the guide 
surface 26 of the collet 10 contacting the tips of the threads and the 
abutting locating surfaces of the insert and socket maintaining the thread 
cutting means 36 in engagement with the threads. The reconditioning tool 
is then rotated relative to the shaft 38, either by hand or with a wrench 
applied to the flats 14, causing the reconditioning tool to advance along 
the shaft axis 40 with the cutting means 36 acting to recondition the 
threads and/or remove foreign matter from between the threads. After the 
threads have been reconditioned, the threading tool is disengaged from the 
shaft 38 by pulling the collet 10 away from the threading insert 12 and 
then off the end of the shaft, and removing the threading insert 12. 
In the example shown in FIG. 4, the reconditioning tool is shown 
reconditioning the threads near the middle portion of the threaded shaft 
38. The reconditioning tool is equally suited for reconditioning the 
threads at or near the end of the threaded shaft where it is generally 
difficult to properly start a one-piece threading die. The thread 
reconditioning tool is assembled to the threaded shaft adjacent the 
damaged end threads and unscrewed from the shaft, causing the thread 
cutting means 36 to recondition the end threads. 
An alternate embodiment of the present invention is shown in FIGS. 6 and 7 
and includes a threading collet 10a and a retainer 12a which are adapted 
to be assembled together as shown in FIG. 8 to form a second embodiment of 
the thread reconditioning tool. 
As in the case of the embodiments of FIGS. 1-5, the collet 10a of FIG. 6 
has a plurality of flat sides 14a disposed about a central axis 16a to 
define a hexagonal element. The collet 10a has an opening or bore 18a 
formed therethrough and a socket 20a formed on one side of the bore. The 
socket 20a, which is adapted to receive a retainer 12a as described below, 
has a semi-cylindrical configuration which is defined by a peripheral 
diameter surface 22a, two diametric locating flats 23a and 24a, and a 
bottom surface 25a. Thread cutting means 36a are formed on the inside 
diameter portion of the throughbore 18a opposite from the socket 20a. The 
thread cutting means 36a include, in the preferred form, two sets of 
thread cutters separated by relief cutouts or flutes as is well known in 
the art. 
The retainer 12a, which has a semi-cylindrical form as shown in FIG. 7, is 
disposed about a central axis 28a and is defined by an outer diameter 
surface 30a, two flats 31a and 32a, and an inside diameter surface 26a. 
The outside diameter surface and the diametric flats, 30a-32a, of the 
retainer 12a and the peripheral locating surface and flats, 22a-24a, of 
the collet 12a constitute locating surfaces which are adapted to cooperate 
with one another to retain the retainer 12a in the socket 20a during 
reconditioning as described below. The smooth inside diameter surface 26a 
functions as a guide surface which is adapted to contact the tips or 
distal portions of the threads on the threaded shaft and thereby maintain 
the thread cutting means 36a in engagement with the threads. 
The retainer 12a and collet 10a are adapted to be assembled together as 
shown in FIG. 8 with the outside diameter surface and the diametric flats, 
30a-32a, of the retainer 12a abutting the cooperating locating diameter 
and flats, 22a-24a, of the socket 20a. As in the case of the first 
embodiment, the respective dimensions of the various locating surfaces are 
chosen such that a sliding fit exists between the retainer 12a and the 
collet 10a for convenient insertion and removal of the retainer. When the 
collet 10a and the retainer 12a are assembled, the retainer is held in the 
socket 20a for rotation with the collet with the guide surface 26a 
maintained in a fixed, spaced relationship relative the cutting means 36a. 
With the collet 10a and the retainer 12a assembled as described, the 
smooth inside guide surface 26a of the retainer 12a is adapted to contact 
the tips of the threads to be reconditioned and thereby retain the shaft 
in engagement with the thread cutting means 36a on the inside surface of 
the collet 10a. The physical relationships of the cutting means 36a to the 
locating surfaces and the guide surface 26a are selected such that the 
cutting means 36a will effect the desired reconditioning when the tool is 
used to recondition a threaded shaft as described below. 
The reconditioning tool of FIGS. 6-8 may be used to recondition the threads 
of a threaded shaft 38 as shown in FIGS. 9 and 10 by placing the collet 
10a over the ends of the threaded shaft 38 and moving the collet 10a to a 
position along the shaft 38 adjacent to the threads-Y-to be reconditioned. 
The retainer 12a is then inserted to its socket 20a. As shown in FIG. 10, 
the retainer 12a and the collet 10a are retained on the threaded shaft 
with the guide surface 26a of the retainer 12a contacting the tips of the 
threads and the cutting means 36a on the inside diameter surface of the 
collet 10a engaging the threads. The assembled tool is then rotated 
relative to the shaft 38, either by hand or with a wrench applied against 
the flats 14a, causing the tool to advance along the shaft axis 40 and the 
cutting means 36a to recondition the threads. 
Another alternate embodiment of the present invention is shown in FIGS. 11 
and 12 and includes a threading collet 10b and an axially extended 
retainer 12b which are adapted to be assembled together as shown in FIG. 
12 to form a third embodiment of the thread reconditioning tool. 
As shown in FIG. 11, the threaded collet 10b has a generally circular 
configuration with a bore 18b and a guide channel 42 formed therethrough. 
The diameter of the bore 18b, as in the case of the above described 
embodiments, is preferably equal to the major diameter of the threaded 
member to be reconditioned and a selected clearance dimension. The guide 
channel 42, has a generally semi-circular form, is defined between an 
outer locating surface 22b and two diametric flats 23b and 24b. Thread 
cutting means 36b, which may be identical to the previously described 
cutting means 36 and 36a, are located on the side of the bore 18b opposite 
the guide channel 42. 
The extended retainer 12b, which may be formed as a unitary structure, 
includes a head 44 and a body 46 both of which are formed along a 
longitudinal axis 48. The head 44 is hexagonally-shaped with the flats 14b 
adapted to cooperate with a suitable wrench. The body 46 extends axially 
of the head 44, as a semi-cylindrical form defined by an outer locating 
surface 50 and diametric flats 51 and 52. A coaxial throughchannel 48 is 
formed along the longitudinal axis 48 of the extended retainer 12b and 
appears as a bore 54 formed through the head 44 and as a semi-cylindrical 
groove 56 formed in the body 46. The diameter of the coaxial channel 48 is 
preferably selected such that it is equal to the major diameter of the 
threaded member to be reconditioned and a preselected clearance dimension. 
The threading collet 10b and the extended retainer 12b are assembled as 
shown in FIG. 12 where the body 46 portion of the extended retainer 12b is 
inserted into the guide channel 42. The respective dimensions of the body 
44 and the guide channel 42 are selected such that a sliding fit exists 
between them. 
The assembled tool may be used to recondition threads in a manner similar 
to that described for the embodiment for FIGS. 6-10. The threading collet 
10a is positioned at the desired location along the threaded manner, the 
extended retainer 12b placed over the shaft and assembled to the threading 
collet 10b, and the assembled tool rotated to effect the reconditioning as 
described above. 
In the embodiments described above, the assembled reconditioning tool is 
rotated by hand or by means of a wrench applied to the flats 14, 14a, and 
14b. However, the tool may also be rotated by other means, as for example, 
by securing a radially extending handle or diametrically extending handles 
to the collet to facilitate rotation, and, in addition, handle means may 
also be secured to the threading inserts or retainers to facilitate 
insertion and removal. While the tool elements of the various embodiments 
have been described as separate elements, it is also possible to connect 
the elements with a flexible or resilient band or connection to prevent 
unwanted separation of the tool elements. Also, the various locating 
surfaces of one or both of the tool elements in the above described 
embodiments may be slightly tapered with respect to their longitudinal 
axis such that the assembled tool can accommodate tolerance variations in 
the threaded member. 
As can be seen from the above, the present invention provides a thread 
reconditioning tool of very simple construction, which is easy to use and 
inexpensive to manufacture. The tool can be quickly located at a selected 
position on a relative long threaded shaft thereby overcoming the 
disadvantages associated with one-piece threading dies, and can quickly 
engage and disengage the threaded shaft without need for any type of 
adjustment thereby overcoming the disadvantages associated with adjustable 
multi-part dies and adjustable thread reconditioning tools. 
As is apparent to those skilled in the art, various changes and 
modifications may be made to the thread reconditioning tool of the present 
invention without departing from the spirit and scope of the present 
invention as recited in the amended claims and their legal equivalent.