Hook cutout for tangless helically coiled insert

A helically coiled wire insert of the type used for tapped holes in parent material that is generally softer than the bolt being screwed into the tapped hole, whereby the two free end coils have a hook recess on the inner screw thread of each and the terminal end of each free end coil has a reduced transverse cross section along one longitudinal axis of the wire. The surfaces of the hook recess are angled from the longitudinal axis of the insert to provide increased forces along the longitudinal axis of the insert.

BACKGROUND OF THE INVENTION 
This invention relates to wire coil screw thread inserts for tapped holes 
of workpieces and, more particularly, to an improved tangless wire coil 
insert. 
The conventional wire coil screw thread insert is provided, at one of its 
ends, with a diametrical tang of its end convolution so arranged that the 
tang can be gripped by a special tool projected through the coil for 
insertion of the wire coil insert into a tapped hole. The tang must be 
broken off and removed after the insertion of the coil insert because the 
tang would prevent a bolt from being screwed through the coil. 
Accordingly, a notch is provided on the inside of the end convolution of 
the coil so that the tang of the coil insert may be broken off. It is 
evident from such previously known devices, that the broken tang must be 
accounted for in certain critical applications, e.g. in electronic 
equipment in which the loose metal tang could cause an electrical short or 
in internal combustion engines where the loose metal tang could cause 
engine failure. Further, the extraction of prior art inserts required the 
use of an extracting tool which cut into the inner threads of the insert 
and thus rendered the insert unusable for further service. 
Further, the problem with prior art inserts, such as tangless inserts as 
described in U.S. Pat. No. 2,363,789 is that they require the one end 
convolution having the recessed hook means therein to project inwardly to 
avoid the possibility of causing burrs or otherwise injuring the tapped 
thread during the insertion of the helically coiled insert. Also, the 
extraction of these tangless coil inserts which must be done by using a 
knife-edge tool damages the inner threads so that the insert cannot be 
reused. 
The method used for inserting a prior art wire coil insert into a tapped 
hole required an operator to manually orientate the insert to be able to 
apply a torque to the lead end of the coiled insert during the insertion, 
since the tang or recessed hook means was only at one end of the insert. 
Thus, there exists a need for a double-ended tangless wire coil screw 
thread insert which can be inserted into the parent material in either 
direction, without regard to orientation, and can be subsequently removed 
without damage to the insert and does not require the accountability of 
broken tangs. 
SUMMARY OF THE INVENTION 
The present invention is directed to a tangless helically coiled insert, 
and is summarized in the following objects: 
First, to provide an insert which an operator may install without 
orientating the insert in one particular direction with respect to the 
ends. 
Second, to provide an improved insert which will permit easy insertion 
thereof and prevent galling of the parent material. 
Third, to provide an insert having recessed hook means at both free end 
coils to facilitate insertion and removal of the insert without damage to 
the insert or the parent material. 
Fourth, to provide an insert whereby no secondary operations are required 
to remove and account for an unnecessary tang. 
Fifth, to provide an insert having recessed hook means at both free end 
coils, whereby the camming surface of the hook means, along the 
longitudinal length of the wire, is at an angle to the vertical along the 
longitudinal length of the wire in order that the pawl or gripper means of 
the installation tool will provide a force along the longitudinal axis of 
the insert. The force along the longitudinal axis of the insert keeps the 
free end coil in close proximity to the next adjacent convolution of the 
insert. 
Sixth, to provide an insert having recessed hook means at both free end 
coils with a lead surface that has an angle to the vertical along the 
transverse width of the wire to provide a force along the longitudinal 
axis of the insert when the hook means is engaged with the pawl or gripper 
means of an installation tool. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this specification. For a better understanding of the invention, its 
operating advantages and specific objects obtained by its use, reference 
should be had to the accompanying drawings and descriptive matter in which 
there is illustrated and described a preferred embodiment of the invention 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is particularly adapted for use in instances where a 
steel alloyed bolt having conventional threads is desired to be fastened 
into a material of relatively softer alloy, such as aluminum. The tapping 
of the threaded hole in the parent material will not ordinarily provide a 
sufficiently firm fastening means. Accordingly, a helically coiled insert 
of material similar to the bolt is inserted in the tapped hole to provide 
adequate locking means in order that the bolt may be inserted and removed 
repeatedly without doing severe damage to the parent material. 
In accordance with the present invention, as shown in the drawings, there 
is depicted a helical coil insert 10 which is wound having any degree of 
advance corresponding to the advance for a particular threaded member with 
which it is designed to cooperate. Thus, for various thread sizes and for 
various diameters of threaded members, the insert 10 may have slightly 
different dimensions. Although the preferred embodiment shows a wire coil 
having a generally diamond-shaped cross-section, it is to be understood 
that the invention is applicable to coils of wire cross-section of any 
form such as square, round, or triangular. What is important, however, is 
that both free end convolutions 12 are so formed that they constitute a 
recess or grip means 14 formed from an angled surface 29 along the 
longitudinal length of the wire and/or an angled lead surface 28 along the 
transverse dimension of the wire, for a suitable insertion and extraction 
tool. 
When the insert 10 is to be inserted in a tapped hole, or a boss, or nut, 
the tool is first inserted into the insert from either free end 12 so that 
a pawl or gripper portion, which pivots from the tool 18, engages the 
recess 14 of the insert 10 which, then, may be screwed by means of the 
tool 18 into the tapped hole. The pivotal pawl has an angled surface 
complimentary to the angled surface of the recess 14 to ensure proper 
contact of the mating surfaces. In certain smaller sizes of inserts it has 
been found necessary to use a special tool having a prewinder sleeve in 
which the insert is first placed, without regard to orientation, so that 
the insert can be reduced in diameter prior to being screwed into the 
tapped hole. In screwing the insert 10 into the tapped hole, the torque 
applied by the tool to the recess 14 will generally cause a contraction of 
the free end convolution 12 and, at the same time, a force having a 
component along the longitudinal axis of the insert which tends to keep 
the free end convolution in contact with the next convolution of the 
insert, so that during the insertion, first, the terminal end 16 will 
enter the tapped hole whereupon the free end convolution 12 and the 
remaining convolutions 13 of the insert body will follow. When the torque 
is relieved, the coil convolutions will expand to be firmly seated in the 
tapped thread. The seating of the free end convolution 12 in the tapped 
thread will prevent, when screwing a bolt into the insert 10, the danger 
of the bolt taking the insert 10 along if the friction between the bolt 
and the recess 14 is very high. 
A terminal end 16 of the free end convolutions 12 constructed in accordance 
with a preferred embodiment of the invention is illustrated in FIGS. 2, 3 
and 6. A truncated portion or free end, being slightly reduced along the 
longitudinal axis of the wire forms the terminal end 16 at both free end 
convolutions 12. The truncated ends are preferably formed with an angle A 
between 10.degree.-15.degree. included between a line B tangent to the 
rear portion of the truncated end 24 and a line C formed by the outer 
crest of the diamond-shaped wire. A lesser angle X is included between a 
line Y tangent to the inner circumference at the rear portion 24 of the 
truncated end and a line Z coextensive with the inner crest 26 of the 
diamond-shaped wire. The purpose of the truncated portion of the terminal 
end 16 of the insert is to prevent sharp edges from shaving metal during 
installation of the insert into a tapped hole. The truncated portion also 
permits the installation tool to be reinserted in an inserted coil or 
permits an extraction tool to be inserted in a coil to be removed. 
The terminal end 16 of the insert 10 may be rounded off in the form of a 
truncated cone. Again, this configuration would prevent sharp edges from 
shaving metal from the parent material during installation of the insert 
into a tapped hole. 
Referring again to FIG. 3, there is shown a recess 14 which receives an 
outwardly biased pawl (not shown) from the extraction tool or insertion 
tool 18 which provides the necessary torque to screw the insert 10 into or 
out of the parent material. The recess 14 has a lead wall portion 28 
generally raked between 5.degree.-15.degree. from a vertical transverse 
plane as seen in FIGS. 3 and 5. This angular rake insures that the gripper 
pawl of the insertion tool 18 is fully inserted into the recess 14 in 
order to cause a torsional force on the free end convolution 12 so that 
the free end convolution 12 will be contracted during the insertion of the 
helically wound insert 10. As illustrated in FIGS. 3-8, the camming 
surface 29 of the recess 14 is kept to a minimum to increase the bolt 
surface strength area for an inserted bolt, thus reducing pullout of the 
bolt. The camming surface 29 is further cut or machined to provide an 
angled surface .alpha. with respect to the longitudinal axis of the wire. 
This angled cut is generally between 2.degree.-20.degree. whereas, in 
FIGS. 3-5, the angle of the lead wall portion is 0.degree.. 
In the embodiment of FIGS. 6-8 the recess 14 also has an angled lead wall 
portion 28. The lead wall portion forms an angle .beta. with respect to 
the vertical axis or the transverse dimension of the wire. This angled cut 
is generally between 2.degree.-20.degree.. 
The insert of the present invention results in a helically coiled insert 
which is readily adaptable to fully automatic operations since the insert 
10 can be inserted with either free end convolution being the lead thread 
and insures a stronger insert with less pullout. 
As seen in FIGS. 3-8, the camming surface may be angled while the lead wall 
may be straight cut, or both the camming surface and the lead wall may be 
angled. Further, the lead wall may be angled while the camming surface may 
be straight cut. However, the angled recess 14, which mates with a 
corresponding angled surface on the pawl of a tool, provides an axial 
force component along the longitudinal axis of the insert, thereby 
providing an increase in force to contract the lead coil and keep the lead 
coil in contact with the next convolution of the insert. 
Finally, it will be clear that the two free end convolutions 12, each with 
a recess 14, will permit removal of the insert 10 from the parent material 
by inserting an extraction tool into the insert 10 in order that the pawl 
of the tool engages the recess 14 opposite the recess used to insert the 
coiled insert 10. Again, the torque applied to the insert 10 by the tool 
in the opposite direction for insertion will cause contraction of the free 
end convolution during removal of the insert.