Connecting device for detachably maintaining flat structures perpendicular to each other

A connecting device for detachable connection of two perpendicularly positioned panels, such as furniture panels, by means of a grooved fastener bolt fastened in the first panel and a tightening bolt rotatably mounted in a blind bore of the second panel. The tightening bolt is mounted in a first blind bore in the second panel and the fastener bolt is adapted to be inserted into a second blind bore in the second panel perpendicular to the first bore. The tightening bolt is in operative engagement with the head of the fastener bolt in such a manner that as the tightening bolt is rotated the fastener bolt is pulled into the second blind bore firmly joining the two panels.

BACKGROUND OF THE INVENTION 
This invention relates to a connecting device for detachably joining two 
boards or panels in a perpendicular relationship to each other, 
particularly furniture panels, in which the first panel is fitted with a 
fastener bolt having a head set apart from the shank by a circumferential 
groove and the second panel is provided with a first blind bore for 
rotatably receiving a cylindrical tightening member. The fastener bolt is 
inserted into a second blind bore provided in the second panel, whereby 
the axis of rotation of the tightening member and the axis of the first 
blind bore receiving such tightening member are perpendicular to the 
longitudinal axis of the fastener bolt and the second blind bore and are 
lying in the plane extending through the longitudinal axis of the fastener 
bolt and the first blind bore receiving the fastener bolt. The tightening 
member is in operative engagement with the head of the fastener bolt in 
such a manner that, as the tightening member is rotated, the fastener bolt 
is pulled into the appropriate blind bore, whereby the two panels are 
joined. Except for the grooved bolt section, the shank and the head of the 
fastener bolt have the same diameter. 
The tightening member is provided with a tightening bore extending 
transversely to its axis of rotation and providing a proper fit for the 
head of the fastener bolt, and with an adjacent tightening slot the edges 
of which extend into the grooved section of the fastener bolt. 
A detachable connecting mechanism of this general type is disclosed in 
German Patent Specification DE-OS No. 22 02 906. In this disclosure, the 
tightening member is in the form of a latch embracing the head of a 
fastener bolt from both sides with tightening discs or plates parallel to 
the plane of the second panel and guiding the bolt head in a 
circumferential slot. As the tightening latch is rotated, a force 
component acts also on the fastener bolt in the direction of rotation of 
the latch, which leads to a displacement of the bolt along its 
longitudinal axis with respect to the axis of rotation of the tightening 
latch. This has the result of the second panel being shifted sideways from 
the first panel during the tightening procedure. Moreover, in order to 
obtain a sufficiently large tightening distance, the diameter of the 
tightening latch must be substantially larger than the diameter of the 
fastener bolt. 
German Patent Specification DE-OS No. 30 28 684 discloses a tightening 
member likewise in the form of a bolt. However, the type of tightening 
member taught by this disclosure requires a specific lateral relocation of 
the blind bores in the second panel. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a connection device of 
the foregoing type in which a clearly defined axial adjustment of the 
fastener bolt toward the axis of rotation of the tightening member is 
achieved by means of a tightening member having a small diameter and with 
the orientation of the axis of rotation of the tightening member with 
respect to the longitudinal axis of the fastener bolt being maintained. 
This is accomplished according to the present invention in that the head of 
the fastener bolt is in the form of an at least hemispherically shaped 
cap, the curved side of which forms a part of the wall of the tightening 
groove, and that the tightening member is in the shape of a tightening 
bolt. The tightening bore is cylindrical in shape up to the axis of 
rotation of the tightening bolt and then merges into a hemispherical 
shaped cup. The tightening slot runs the entire length of the side wall of 
the tightening bolt up to the lowest point of the hemispherical cup 
forming part of the tightening bore. 
In this construction of the fastener head of the fastener bolt and the 
tightening bore of the tightening bolt, the fastener head inserted into 
the tightening bore is guided on all sides except for the cutout forming 
the tightening slot, so that the laterally acting force components are 
intercepted and lateral dislocation of the fastener bolt is safely 
prevented. The longitudinal axis of the fastener bolt remains in proper 
orientation to the axis of rotation of the tightening bolt throughout the 
entire fastening procedure or distance covered by the fastener bolt. The 
tightening slot in this construction permits utilization of the entire 
distance available for the adjustment of the fastener head in the bore of 
the tightening bolt. Moreover, the extent of the locking movement is 
limited by the tightening slot of the tightening bore in the tightening 
bolt, and since the tightening bore is opened by the slot from one side 
only, the tightening bolt is prevented from being turned back past the 
input position of the fastener bolt. Thus, the input position 
simultaneously defines also the open or unlocked position of the 
connecting members. 
A sufficiently large abutment surface of the bore in the tightening bolt 
for engagement with the head of the fastener bolt is obtained according to 
one embodiment, in that the hemispherical cap has a radius which 
corresponds to the radius of the fastener bolt so that the diameter of the 
tightening bore and the hemispherical cup forming a part of the tightening 
bolt likewise correspond to the diameter of the fastener bolt. 
A positive self-locking end position of the locking movement of the 
tightening bolt is achieved according to another embodiment, when the 
construction is such that the end portion of the tightening slot of the 
bore of the tightening bolt terminates in a semicircular abutment section 
having a radius which corresponds to about one-half of the width of the 
tightening slot. 
To sufficiently secure the fastener head to the shank of the fastener bolt, 
a further embodiment of the invention provides for the diameter of the 
grooved section of the fastener bolt and thus the width of the tightening 
slot of the tightening bolt to be about one-third of the diameter of the 
fastener bolt.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIGS. 1 and 2 show first panel 15 with fastener bolt 10 fastened therein. 
This is accomplished by introducing fastening section 14, having barbs or 
catches, into blind bore 16 in first panel 15, until shoulder 13 on the 
shank of bolt 10 rests against first panel 15. Fastener head 12 is in the 
shape of a hemispherical cap, the curved side of which forms a part of the 
wall of an attachment groove and the plane side forms the end portion of 
fastener bolt 10. Fastener head 12 has the same diameter as the shank of 
fastener bolt 10. The hemispherical cap-shaped head 12 merges into 
cylindrical grooved section 11, the radius of which is smaller than the 
radius of the adjacent shank portion of fastener bolt 10. The stepped 
transitional section between cylindrical grooved section 11 and the shank 
of fastener bolt 10 forms the other wall of the attachment groove. The 
diameter of cylindrical grooved section 11 corresponds to about one-third 
of the diameter of fastener bolt 10 so that fastener head 12 is 
sufficiently firmly joined to the shank of fastener bolt 10. Slot 22 of 
tightening bore 21 in tightening bolt 20 are of the same dimensions. The 
fastener bolt 10 is inserted into blind bore 18 in second panel 17. Blind 
bore 18 is located in the middle of the front edge of second panel 17 and 
extends parallel to its faces. The diameter of blind bore 18 is adapted to 
accommodate the exposed length of fastener bolt 10 fastened to first panel 
15 so that fastener bolt 10 is axially adjustable in blind bore 18 a 
distance such that the second panel is capable of being tightly joined to 
first panel 15. 
This is accomplished by means of tightening bolt 20. Tightening bolt 20 is 
rotatably mounted in blind bore 19 drilled from one face into second panel 
17. The axis of rotation 25 of tightening bolt 20 lies in a plane which is 
perpendicular to the longitudinal axis 24 of fastener bolt 10 and the axis 
of blind bore 18 receiving tightening bolt 20, so that these two axes 
intersect. This particular orientation of the blind bores 18 and 19 
facilitates their being drilled into second panel 17. Moreover, the 
tensioning forces transferred from tightening bolt 20 to fastener head 12 
of fastener bolt 10 act along the longitudinal axis 24 of fastener bolt 10 
whereby any canting and jamming of fastener bolt 10 in blind bore 18 is 
prevented. Tightening bolt 20 is inserted into blind bore 19 in such a 
manner that its face having slot or notch 23 therein is flush with the 
face of second panel 17. The manner as to how tightening bolt 20 is put 
into operative engagement with fastener bolt 10 and the particular 
mechanics of such operative engagement will be described with reference to 
FIGS. 3 to 5. 
Tightening bolt 20, shown in a side view in FIG. 5, is provided with a 
tightening bore 21 directed transversely to the axis of rotation 25. The 
diameter of bore 21 is such as to accommodate the diameter of fastener 
bolt 10. To enable the head 12 of fastener bolt 10 to be inserted into 
tightening bore 21, tightening bolt 20 needs to be so oriented that the 
bore axis 27 coincides with the longitudinal axis 24 of fastener bolt 10. 
To facilitate insertion of fastener bolt 10, tightening bore 21 may be 
provided with a conically enlarged inlet opening 29. In this input 
position shown in FIG. 3, it is possible to insert head 12 of fastener 
bolt 10 into tightening bore 21 of tightening bolt 20 a distance until the 
second panel 17 is drawn to and abuts first panel 15. Thereupon, 
tightening bolt 20 is rotated clockwise into its locking position, as 
shown in FIG. 4. In so doing, head 12 of fastening bolt 10 is drawn some 
distance into tightening bore 21 of tightening bolt 20 until second panel 
17 is tightly secured against first panel 15. 
In order to obtain a sufficiently long tightening distance, the diameter of 
tightening bolt 20 is larger than the diameter of fastener bolt 10 and 
corresponds to about 1.5 to 2 times the diameter of fastener bolt 10. 
Tightening bore 21 extends up to the axis of rotation 25 of tightening 
bolt 20 and past that point terminates in a hemispherical cup 28 of the 
same radius, as it is clearly shown in FIGS. 3 and 4. To enable tightening 
bolt 20 in operative engagement with head 12 of fastener bolt 10 to be 
rotated in tightening bore 21, slot 22 is provided to open the tightening 
bore 21 including its hemispherical end section 28 from one side for 
tightening slot 22 to receive and guide grooved section 11 of fastener 
bolt 10. 
As is shown in FIG. 5, slot 22 intersects a semi-cylindrical portion of 
tightening bolt 20 in a plane which is perpendicular to the axis of 
rotation 25 of tightening bolt 20 and parallel to axis 27 of tightening 
bore 21. The section of slot 22 facing away from the input opening of bore 
21 extends with its semicircular abutment 26 past the middle of tightening 
bolt 20 so that in the terminal locking position longitudinal axis 24 of 
fastener bolt 10 again is in alignment with axis 27 of bore 21. FIG. 4 
clearly shows that the axial length of grooved section 11 of fastener bolt 
10 is equal to one-half of the difference between the diameter of 
tightening bolt 20 and the diameter of fastener bolt 10. Moreover, the 
width of the slot 22 should correspond approximately to the diameter of 
cylindrical grooved section 11 of fastener bolt 10, and semicircular 
abutment 26 has a radius which corresponds to one-half of the diameter of 
grooved section 11 of fastener bolt 10. Thus, tightening bolt 20 is 
capable of being rotated a maximum of 180.degree. from the input or open 
position shown in FIG. 3 into the locked position shown in FIG. 4. 
The rotational movement of tightening bolt 20 is limited, first, by the 
wall portion of tightening bore 21 opposite slot 22, which wall portion 
serves as a stop for head 12 of fastener bolt 10, and secondly, by 
semicircular stop 26 of tightening slot 22 abutting grooved section 11 of 
fastener bolt 10.