Fastener collar removal tool

A tool for removal of round internally threaded collars from high efficiency aerospace fasteners. The tool includes a central cylindrical pin having a head at one end held against rotation, a non-round extension at the second end and a transverse bore intermediate the ends, containing a ball which is spring biased to project slightly beyond the pin wall. A mandrel assembly surrounds the pin and is rotatable relative thereto. A gripping collet is positioned between the mandrel and pin with collet fingers at one end extending beyond the mandrel and a threaded second end threaded into said mandrel. An axial slot in said collet is adapted to receive said ball when aligned therewith to form a releasable latch mechanism. In operation, the open collet fingers are placed over a threaded collar with said extension in engagement with a corresponding recess in the end of the bolt within the collar. The socket and mandrel are rotated in the collar unthreading direction. The latch mechanism latches the pin and collet together, preventing rotation of the collet. This causes the mandrel to thread into the collet and move downwardly forcing the fingers to grip onto the collar and bringing frictional contact between the mandrel and collet. This frictional contact tries to force the collet to rotate with the mandrel, to thus cause the latch to release and the collet to rotate with the mandrel. Continued rotation of the mandrel causes the collet fingers to further tighten on the collar until the collar unthreads from the bolt.

BACKGROUND OF THE INVENTION 
This invention relates in general to tools for disassembling threaded 
fasteners and, more specifically, a tool for removing round collars from 
threaded bolts. 
A fastening system for aerospace structures, as detailed in U.S. Pat. Nos. 
2,940,495 and 3,138,987 has achieved widespread use in the aerospace 
industry due to its simplicity, consistently controlled preload and 
minimum size and weight. The fastener basically consists of two parts, a 
threaded bolt and threaded nut. The nut, which is the key component, 
consists of a internally threaded collar which threads onto the bolt and 
has a bearing surface which engages the structure being fastened and a 
wrenching device which is unitary with the collar and typically has a 
hexagonal cross-section for engagement by a conventional wrench. The bolt 
end has a configured recess, typically hexagonal, so that an Allen wrench 
may be inserted to hold the bolt stationary while the nut is rotated. A 
groove is provided between the wrenching device and the collar so that as 
the device is tightened the wrenching device breaks off at a pre-set 
torque. The break-off torque depends on the depth of the groove, which can 
be selected to meet different torque requirements. 
The collar is a surface of revolution, so that once installed it cannot be 
rotated by conventional wrenches, so that the pre-selected torque cannot 
be later inadvertently changed. This "tamper proof" feature eliminates 
torque inspection after installation. 
Such fasteners are widely available from the Hi-Shear Corporation under the 
"Hi-Lok" trademark and from several Hi-Shear licensees. 
These fasteners are very effective and are intended to be permanently 
installed. Sometimes, however, the fasteners need to be removed due to 
assembly errors, need to repair the structure, etc. Where access is easy, 
a worker generally inserts an Allen wrench into the bolt end socket and 
rotates the collar with locking pliers. However, this technique damages 
the collar, and may damage the structure surface near the fasteners, 
especially if the pliers slip during unthreading. Also, tools must be held 
and operated simultaneously with both hands, requiring some skill and 
increasing the likelihood of errors and tool slips. Most importantly, 
access to a relatively large volume of space around the collar is required 
for these removal tools. Complex aerospace structure often have such 
fasteners in locations such that the collar is in a "well" or "tunnel" 
like areas, making access difficult. Special tools, such as the HLH128 
Removal Tool from the Hi-Shear Corporation basically uses an offset 
cam-type closed end wrench to grip the collar while an Allen wrench 
engages the bolt socket. While this reduces the space needed for access, 
it still requires two-hand, skilled operation and could result in damage 
to adjacent surfaces if errors are made. 
Other tools remove the collar by splitting it with a high pressure wedge 
device such as the collar splitters available from American Pneumatics 
Tool Co. and the Huck Co. While effective, these tools tend to be large, 
heavy and requires considerable access space and require hydraulic or high 
pressure air supplies. Other manually operated collar removal tools, such 
as those available from Continental Air Tools, Inc. operate only in 
interference fit condition and require considerable effort. 
Thus, there is a continuing need for improved devices to operate in both 
interference and loose fit conditions which are lightweight, require 
little skill to use, require little access space around the fastener, 
reduce the risk of damage to adjacent structures, and save time. 
SUMMARY OF THE INVENTION 
The above noted problems, and others, are overcome by the fastener removal 
tool of this invention, which basically comprises a central generally 
cylindrical pin having a head at one end adapted to being held against 
rotation and a key member at the other end, a rotatable drive socket and 
locking mandrel assembly surrounding said pin and a collet threaded into 
the mandrel between the mandrel and pin. A latch arrangement automatically 
locks the collet and pin together as the collet is driven into a clamping 
engagement between the mandrel and a collar positioned within the collet 
fingers. When the fingers are in tight engagement with the collar, the 
latch mechanism releases, allowing the collet to rotate with the mandrel, 
unthreading the collar.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1, there is seen a perspective view of the collar 
removal tool 10 in use removing one of several fasteners 12. Tool 10 is 
mounted for rotation in a conventional air motor drive arm 14 of the sort 
available, for example, from American Pneumatics Tool Co. As is detailed 
below, the tool is placed over the collar 12 with a correspondingly-shaped 
pin (here, hexagonal) engaging recess 18 in bolt 20. The motor is then 
turned on to rotate the tool counter clockwise, to rotate and unthread 
collar 16 from bolt 20. 
Details of tool 10 are shown in FIGS. 2-4, which can be considered 
together. 
FIG. 2 in a view looking upwardly at the collet end of tool 10 without a 
collar 16 in place, FIG. 3 is an axial section view taken substantially on 
line 3--3 in FIG. 2 and FIG. 4 is a detail section view of the ball-detent 
latch mean, taken substantially on line 4--4 in FIG. 3. 
The upper end of mandrel assembly 22 has a non-circular (typically square 
or hexagonal) cross-section to fit in a rotatable receiver in drive arm 
14. Mandrel assembly 22 is held in place by a conventional spring clip 24 
so that mandrel 22 can be rotated by internal drive means (not shown) 
within arm 14. 
While mandrel assembly 22 may be formed as one piece, for greater 
versatility, it is preferred that a two-piece mandrel assembly be used, as 
seen in FIG. 3. Upper portion 26 has a downwardly extending female socket 
28 which receives an upwardly extending male member 30 on lower mandrel 
position 32. Socket 28 and cooperating member 30 have complementing 
non-round cross-sections, typically square or hexagonal, causing both 
portions to rotate together. Lower portion 32 (together with other 
components described below) is sized to fit over a single size of collar 
16. If a different sized collar is to be removed, lower portion 32 can 
easily be replaced with another of the appropriate diameter, as is 
described in greater detail below. 
A cylindrical pin 34 is rotatably located within mandrel assembly 22. Pin 
34 includes a head 36 having a transverse opening 38 into which the end of 
a spring rod 40 can enter. Spring 40 is fastened to arm 14 in a manner 
which biases pin 34 downwardly while preventing rotation of pin 34 
relative to arm 14. 
At the opposite end, pin 34 includes a non-round extension 42 (here, a 
hexagonal end corresponding to an Allen wrench,) adapted to fit a 
complementary socket in bolt 20. While extension 42 may be formed 
integrally with pin 34, it is preferred that extension 42 be on a short 
cylinder 44 which fits in a corresponding bore in the end of pin 34 and is 
held in place by setscrew 46. This permits removal and replacement of 
extension 42 with others fitting different recesses in the ends of 
different bolts 20. 
A collet 48 is positioned between lower portion 32 of mandrel assembly 22 
and pin 34. Collet 48 includes an externally threaded (left-hand threads) 
first end 50 which threads into internal threads in mandrel 32. 
Collet fingers 52 extend downwardly beyond extension 42 and beyond mandrel 
32. Fingers 52 have an outwardly flared surface 54 adapted to engage 
mandrel edge 56 as mandrel 32 is threaded downwardly into collet 48, 
causing fingers 52 to move together in a gripping manner. 
A latch mean 58 (as best seen in FIGS. 3 and 4) is positioned to latch and 
release pin 34 and collet 48 during tool operation. Here, latch 58 
consists of a transverse bore 60 through pin 34 containing a ball 62, a 
spring 64 and a threaded plug 66. The bore 60 has a slightly reduced 
diameter at the ball end to prevent ball 62 from being expelled from pin 
34. 
A vertical slot 68 is adapted to receive the projecting ball when pin 34 
and collet 48 are rotationally positioned with ball and slot in alignment. 
In use, the tool 10 is installed in a drive arm 14, spring rod 40 is 
inserted in opening 38, collet 48 is rotated slightly clockwise so that 
fingers 52 project beyond mandrel 22 and are suitably spaced apart. The 
fingers 52 are placed over a collar 16 to be removed with extension 42 in 
the end socket of bolt 20. Spring 40 permits a limited amount of endwise 
movement of pin 34 so that extension 42 can engage bolt sockets of 
somewhat varying distances below the top of collar 16. 
The drive mechanism of arm 14 is then turned on to rotate mandrel 22 in a 
counterclockwise direction. Collet 48 rotates with mandrel 22 until ball 
62 reaches slot 68, whereupon the ball enters the slot, latching pin 34 to 
collet 48 and stopping collet rotation. 
Continued rotation of mandrel 22 relative to the now-stationary collet 
causes mandrel 22 to thread downwardly into collet 48, causing fingers 52 
to engage mandrel edge 56 and be forced inwardly until they grip collar 
16. Ball 62 moves correspondingly along slot 68. As frictional forces 
between contacted surfaces 56 and 54 increases, ball 62 is forced out of 
slot 68, by the differential rotational forces unlatching latch 58 and 
allowing collet 48 to rotate and unthread collar 16 from bolt 20. 
The force necessary to "pop" ball 62 out of slot 68 further tightens collet 
fingers 52, assuring a firm grip on collar 16. In order to avoid excessive 
ball-release forces it is preferred that the release side of slot 68 be 
slightly chamfered as shown at 70 in FIG. 4. With a 0.080 inch diameter 
ball, about a 0.003 inch chamfer gives best results. 
While the latch embodiment shown in FIG. 4 is preferred for simplicity and 
ease of operation, it may not be optimum in all cases. After a collar 16 
is removed with the tool, the mandrel assembly 22 may be rotated in the 
opposite (clockwise where a conventional collar has been removed by 
counter clockwise rotation) direction. Ball 62 re-enters slot 68 and 
engages the un-chamferred side of the slot, necessitating further 
rotation, loosening finger 52 from mandrel 16. In some cases this force 
will be insufficient and pliers may be required to remove collar 16. Where 
this is a problem, the latch embodiment shown in FIGS. 5-7 may be 
preferred for a more positive collar release. In this embodiment, most 
components are the same as shown in FIGS. 1-3, except that a pivoting 
blade replaces the ball latch mechanism. 
Considering FIGS. 5-7 together, there is seen a pin 134 corresponding in 
general to pin 34 in FIG. 3. In this embodiment, however, rather than 
having an enlarged head 36 at the upper end, an enlarged head or flange 
136 is provided at the lower end. Retaining opening 138 remains in the 
upper end of the pin, to receive spring 40 as seen in FIG. 1. This 
alternative head arrangement allows pin 134 to be inserted from the finger 
52 end of the assembly. Head 136 further aids in preventing collet 48 from 
dropping out of the assembly should it become entirely unthreaded from 
mandrel 22. 
Pin 134 has an axial slot 160 having a semi-circular cutout 161 at one end. 
A blade 163 is pivotably mounted on pin 165 within slot 160 as seen in 
FIGS. 6 and 7. A first end of blade 163 bears a projection 167 having the 
general shape of a quarter-sphere. 
A spring 169 within an axial bore 171 within pin 134 presses a pin 173 
against a sloping end 175 of blade 163 to bias blade 163 towards the 
position shown in FIG. 6, with projection 167 extending beyond the wall of 
pin 134. A moderate force is sufficient to press projection 167 back into 
slot 160 against the force of spring 169. 
In operation, as best seen in FIG. 7, as the collet 48 is rotated 
counter-clockwise as described above, the spherical surface of projection 
167 is brought into contact with the edge of slot 68 and is forced to 
pivot about pin 165 to retract projection 167 as the projection "pops" 
over the slot edge. The collect fingers engage the collar and unthread it, 
as described above in conjunction with the description of FIG. 3. 
Once the collar is removed, the drive motor direction is reversed. Blade 
163 pivots outwardly as projection 167 passes slot 68 so that projection 
167 reenters the slot. As clockwise movement of collet 48 continues, the 
flat side of projection 167 engages the side of slot 68, stopping rotation 
of collet 48 and unthreading collet 48 from mandrel 22, releasing the grip 
of fingers 52 (FIG. 3) on collar 16. Generally, a mere "touch" or "blip" 
on the reverse switch is sufficient to release the collar. If the 
clockwise rotation is continued slightly longer than necessary, collet 48 
may entirely unthread from mandrel 22. Head 136 will prevent collet 48 
from dropping out of the assembly. Collet 48 can then be easily manually 
re-threaded into mandrel 22 prior to the next collar removal operation. As 
seen in FIG. 7, the exterior surface of mandrel 22 can have a hexagonal, 
rather than circular, cross-section if desired. 
While certain preferred components, arrangements and relationships were 
detailed in the above description of a preferred embodiment, those may be 
varied, where suitable, with similar results. For example, the collet 
fingers may be configured to engage collars of other shapes and different 
latch mechanisms could be used, if desired. 
Other variations, applications and ramifications of this invention will 
occur to those skilled in the art upon reading this disclosures. Those are 
intended to be included within the scope of this invention, as defined in 
the appended claims.