Metallic structural element for connecting workpieces consisting of wood, woodworking material or plastic

A metallic structural element for connecting workpieces consisting of wood, woodworking material or plastic, consisting of a lamellar part, which provides the non-positive connection with the first workpiece provided with a groove and a transverse hole, and a bolt-like part which, through screwing or pinning, realizes the non-positive connection with the second workpiece provided with a longitudinal hole. The lamellar part has, in the center, a hole which is at right angles to the plane of the lamella and is intended for fixing in the groove of the workpiece. Variants having a wing-like long or rectangular short lamellar part and a bolt-like part in the form of a conical wood screw, cylindrical screw, screw having a metal thread, threaded sleeve or pin. Accessories: screwing tool and drilling template.

FIELD OF THE INVENTION 
The invention relates to the further development and supplementation and 
completion of the connecting techniques and of the connecting elements 
used here. 
The invention relates in particular to a metallic structural element for 
connecting workpieces consisting of wood, woodworking material, such as 
particle board, laminated board or plastic, based on the groove-and-tongue 
principle. 
PRIOR ART 
Structural elements based on a large number of connecting techniques for 
the assembly of several workpieces are known in interior decorating and in 
joinery, especially furniture making. In general, the object is to join 
more or less flat surfaces of adjacent individual parts to form a whole. 
Such connections may be detachable or nondetachable. The latter include in 
particular glued joints. Most frequently, the basic forms are flat 
surfaces abutting one another or meeting one another at right angles. 
A known type of connection is based on the groove-and-tongue principle. The 
workpieces to be joined are each provided with a continuous groove or 
individual separated narrow slots into which an intermediate piece, the 
so-called "tongue" is inserted. In principle, this is known as keying from 
mechanical engineering. In order to produce a good non-positive 
connection, it is as a rule necessary to glue the tongue to the workpieces 
to be connected, in the groove. Another type of connection consists of the 
so-called clamping iron, a flat lug which is provided with holes and 
becomes a threaded bolt, generally in the form of a wood screw, at one 
end. Another type is the so-called Ringers' bracket, a U-shaped 
cylindrical metal rod which is used generally as a shelf support (e.g. 
bookshelves). 
The known connecting elements are very unsatisfactory. The classical 
groove-and-tongue connection is as a rule not particularly suitable for 
the transmission of relatively large forces. Furthermore, it is very 
seldom detachable without damaging some part involved. The clamping iron 
is unattractive and must be inlet, countersunk and if necessary covered, 
thus involving additional work. The Ringers' bracket can be used only in 
specific cases and is not universally applicable. 
There is therefore a great need for further development of connecting 
elements for, as far as possible, universal use in interior design, 
joinery, the household and the leisure and hobby sector. 
The following documents are cited in connection with the prior art: 
Brochure on clamping irons (cramp irons) 
Brochure on connecting panels "Lamellae" 
Brochure on Haas connection fitments 
Brochure on Ringers' bracket 
Brochure on shelf brackets 
SUMMARY OF THE INVENTION 
It is the object of the invention to provide a metallic structural element 
for connecting workpieces consisting of wood, woodworking material or 
plastic, based on the groove-and-tongue principle, which ensures a 
satisfactory non-positive connection of a plurality of workpieces without 
danger of tearing or breaking off. The connection should include the 
possibility of detachment at any time without any damage to the 
workpieces. The connecting element should be simple and convenient to use 
and to handle, without requiring expensive special additional tools. The 
structural element should be suitable for economical mass production and 
should be as universally applicable as possible. 
This object is achieved if the metallic structural element mentioned at the 
outset consists of a flat lamellar part providing the non-positive 
connection with the first workpiece provided with a groove or a slot and a 
transverse hole and a bolt-like part which, through screwing or pinning, 
provides the non-positive connection with the second workpiece provided 
with a longitudinal hole and which rests on the lamellar part with its end 
face at right angles and is firmly connected to the said second workpiece, 
and if the lamellar part has, at its center, along the axis of the 
bolt-like part, a hole which is perpendicular to the plane of the lamella 
and is intended for fixing the first workpiece by means of a screw or of a 
pin.

DETAILED DESCRIPTION 
FIG. 1 shows a schematic exploded perspective view illustrating in 
principle the composition of the structural element and its arrangement in 
relation to the workpieces to be connected. 1 is a first workpiece 
comprising a vertical wooden board finely worked at least on its end face 
or a corresponding particle board. 2 represents a second workpiece of the 
same material, likewise vertical. The workpieces 1 and 2 are to be 
detachably connected to one another by a butt joint. For this purpose, the 
first workpiece 1 is provided with an arc-like groove 6 parallel to the 
longitudinal edge and arranged approximately in the center and with a 
transverse hole 7 passing through this groove 6. 
The workpiece 2 has in its central part, in the plane of the transverse 
hole 7, a longitudinal hole 8 for receiving the structural element. The 
latter is produced from a metallic material and consists in principle of 
the lamellar part 3 to be lowered into the groove 6 and of the bolt-like 
part 4 which produces the firm connection with the second workpiece 2 via 
the longitudinal hole 8. This bolt-like part 4 thus constitutes the 
non-positive connection with the second workpiece 2 via a screw connection 
or pinning. Instead of being connected flush with the first workpiece 1 by 
a butt joint, said workpiece 2 can of course also be connected at right 
angles to a lateral surface or at any angle. 
FIG. 2 relates to a perspective view of the basic embodiment of the 
structural element having a lamellar part and a bolt-like part in the form 
of a wood screw. Relative to FIG. 1, the structural element is shown 
rotated through 90.degree. with regard to the plane of the lamella and 
rotated through 90.degree. about its main axis. The lamellar part 3 
consists of a flat tab-like wing having an arc shape 9 at its outer 
contour and is provided with a taper 12 toward the ends of the wing. At 
its inner contour, the lamellar part 3 has a flat stop 10, adjacent to 
which is a step 11. The hole 5 whose axis is perpendicular to the plane of 
the lamella is present in the plane of symmetry of the structural element, 
which plane is defined by the axis of the bolt-like part 4. The outer 
contour (arc 9) of the lamellar part 3 has two notches 14 for receiving 
the beads 15 of the screwing tool (cf. FIG. 8). These notches 14 prevent 
lateral slipping of the screwing tool during fixing of the structural 
element in the second workpiece 2. Here, the bolt-like part 4 is in the 
form of a wood screw 16 having a conical thread. 
FIG. 3 shows a perspective view of a special embodiment of the structural 
element for compact use in corners of the workpieces. This is essentially 
the basic embodiment according to FIG. 2 but with cut-off wings of the 
lamellar part 3. The latter once again has the stop 10, the steps 11, the 
hole 5 and the notches 14. Apart from the arc-shaped outer contour, the 
lamellar part 3 is essentially a rectangle 13. In the present case, the 
bolt-like part 4 is once again a wood screw 16. 
FIG. 4 shows a perspective view of an embodiment of the structural part 
having a bolt-like part in the form of a screw with a cylindrical thread. 
The lamellar part 3 is exactly the same as in FIG. 2. The reference 
symbols 3, 5, 9, 10, 11, 12 and 14 correspond exactly to those in FIG. 2. 
Here, the bolt-like part 4 consists of a screw 17 having a short 
cylindrical thread which is suitable for screwing into an appropriate 
predrilled hole in wood, particle boards, plastic, dowel plugs, etc. 
FIG. 5 relates to a perspective view of an embodiment of the structural 
element having a bolt-like part in the form of a screw with a cylindrical 
metal thread. The lamellar part 3 is exactly the same as in FIG. 2. The 
reference symbols 3, 5, 9, 10, 11, 12 and 14 correspond exactly to those 
in FIG. 2. Here, the bolt-like part 4 consists of a screw 18 having a 
comparatively short cylindrical metal thread which is suitable for 
screwing into an appropriate internal thread in a metal or plastic sleeve 
or in another member provided with an internal thread or in a dowel plug. 
FIG. 6 relates to a perspective view of an embodiment of the structural 
element having a bolt-like part in the form of a threaded sleeve. The 
lamellar part 3 is exactly the same as in FIG. 2. The reference symbols 3, 
5, 9, 10, 11, 12 and 14 correspond exactly to those in FIG. 2. Here, the 
bolt-like part 4 consists of a threaded sleeve 19 (metallic internal 
thread) which is suitable for screwing onto an appropriate metallic 
external thread on a threaded bolt let into the second workpiece 2. 
FIG. 7 shows a perspective view of an embodiment of the structural element 
having a bolt-like part in the form of a pin. The lamellar part 3 is 
exactly the same as in FIG. 2. The reference symbols 3, 5, 9, 10, 11, 12 
and 14 correspond exactly to those in FIG. 2. Here, the bolt-like part 4 
consists of a pin 20 or a smooth tube for insertion into an appropriate 
smooth hole in the second workpiece 2 (plug connection). 
FIG. 8 shows a perspective view of a screwing tool. This screwing tool 
serves for fixing the structural element according to the embodiment in 
the FIGS. 2, 3, 4, 5 and 6 in the second workpiece 2 by screwing in. The 
screwing tool is suitable for insertion or clamping in a rotating 
mechanical hand tool (for example a drill). It consists of a shaft 21 for 
clamping in the hand tool, in the present case in the form of a hexagon, a 
head 22 having a transverse groove 23 for receiving the lamellar part 3 of 
the structural element to be screwed in and two beads 15 at the bottom of 
the transverse groove 23, which engage the notches 14 of the lamellar part 
3. The beads 15 prevent the screwing tool from slipping off sideways from 
the structural part during the screwing process. The shaft 21 can of 
course also have a different cross-section, for example it may be any 
polygon or a circle. 
FIG. 9 shows a perspective view of a drilling template. This drilling 
template serves for guiding the drill during production of the transverse 
hole 7 in the first workpiece 1. For this purpose, it is placed flush in 
the groove 6 cut out beforehand. The drilling template consists of a 
plate-like arc-shaped template 24 for placing in the groove 6, the stop 
part 25 which is to be placed against the end face of the first workpiece 
1, and the counter-plate 26. At least the latter has the drill bush 27. In 
the present case, the arc-shaped template 24 also has a drill bush in 
order to permit drilling of the first workpiece 1 in one operation. A 
cut-out 28 through which the center mark 29 (perpendicular line with 
arrow) is visible is provided for better monitoring. 
Embodiment 1 
See FIGS. 1 and 2 
The structural element is according to FIG. 2 and consists of low-carbon 
steel which permits a high degree of cold working during production. The 
lamellar part 3 is punched and the bolt-like part 4 is cold-worked from 
wire rod. Parts 3 and 4 are butt-welded and the raw finished part is 
burred, cleaned, machined and then pickled. The surface of the structural 
element is chromium-plated for protection against corrosion and oxidation. 
The dimensions are: 
lamellar part 3: W=57 mm; H=12 mm; D=4 mm 
bolt-like part 4: L=40 mm; D=5 mm 
The workpieces 1 and 2 to be joined consist of oak wood with an end face of 
22 mm.times.150 mm. The connection is a butt joint at the end faces, 
according to FIG. 1. The groove 6 in the workpiece 1 is produced by means 
of a circular saw of 100 mm diameter and is cut 13 mm deep and 4 mm wide. 
The transverse hole 7 in the workpiece 1 is drilled through from the stop 
side in the middle of the end face and has a diameter of 5 mm. A steel 
screw having a length of 18 mm and a diameter of 5 mm is present in the 
transverse hole 7 for securing. The longitudinal hole 8, which has a 
length of 40 mm and a diameter of 3 mm, is present in the workpiece 2, 
perpendicular to the end face (predrilled for receiving the bolt-like part 
4). 
The structural element is screwed into the workpiece 2 by means of the 
screwing tool (cf. FIG. 8) with a 4.5 mm wide transverse groove 23. For 
this purpose, the screwing tool is clamped in a drill. The transverse hole 
7 in the workpiece 1 is drilled with the aid of the drilling template (cf. 
FIG. 9). The radius of the arc-shaped template 24 is 50 mm and the 
internal diameter of the drill bush 27 is 5.2 mm. The stop part 25 has an 
internal diameter of 9 mm. 
The total time required for joining the workpieces 1 and 2 is about 6 
minutes. 
Embodiment 2 
See FIG. 2 
The structural element produced according to Example 1 and having the same 
dimensions corresponds to FIG. 2. In contrast to FIG. 1, the present case 
relates to the fixing (detachable connection) of a shelf to a 
perpendicular wooden wall (angular joint). The shelf corresponds to the 
workpiece 1 and the wall to the workpiece 2. The workpieces are machined 
analogously to Example 1. First, the longitudinal hole 8 is predrilled 
horizontally into the perpendicular wall (workpiece 2) and the wood screw 
16 (bolt-like part) of the structural element is screwed into the wall. 
The groove 6 is cut into the longitudinal side of the shelf to be 
positioned horizontally (workpiece 1), and the transverse hole 7 is 
drilled in said shelf. The shelf is then pushed onto the lamellar part 3 
of the structural element and secured with a screw in transverse hole 7. 
The nondetachable fixing of a wooden shelf to a perpendicular wall should 
be mentioned here as a variant of this Example. Said wall is provided with 
a number of dowel plugs, in which the holes 8 are predrilled. The 
structural element used is one having roughened ("structured") lateral 
surfaces of the lamellar part 3. Before the shelf is inserted/pushed on, 
glue is applied in the corresponding grooves 6. 
Another possibility here is the detachable fixing of a shelf in a recess, 
the end faces of the shelf being provided with continuous grooves 6 for 
insertion via the lamellar parts 3. 
The detachable or nondetachable connection of perpendicular walls of any 
kind which meet one another at right angles is a further variant of this 
Example (angular joint). 
Embodiment 3 
See FIG. 3 
The structural element is according to FIG. 3 and consists of low-carbon 
steel which has a high degree of cold-workability. The blank consists of 
wire rod which has been hot-upset, pressed flat and then cold-worked. The 
raw finished part is burred, cleaned, machined and chromium-plated to 
increase the corrosion resistance and stability to oxidation. 
The dimensions are: 
lamellar part 3 (rectangle 13): W=17 mm; H=15 mm; D=4 mm 
bolt-like part 4 (wood screw 16): L=40 mm; 
The workpieces 1 and 2 to be joined consist of walnut wood, the workpiece 2 
representing a corner in the adjacent perpendicular walls of a piece of 
furniture and workpiece 1 representing a detachable shelf (double angular 
joint). The procedure is similar to Examples 1 and 2. The walls forming 
the corner are each provided with a longitudinal hole 8 for receiving the 
bolt-like part 4 (wood screw 16) of the structural element. The screwing 
tool is used for screwing in. A groove 6 is cut and a transverse hole 7 is 
drilled in the end face and in the longitudinal side of the shelf. The 
shelf is pushed onto the lamellar parts 3 of the structural elements and 
secured with screws. 
The structural element according to FIG. 3 is used wherever there is no 
space for a broad, wing-like lamellar part 3 according to FIG. 2 and 
furthermore where there is no possibility or necessity for producing a 
groove 6 for the workpiece 1: corners, feet, consoles, bases, etc. of 
furniture at the wall or floor. 
Embodiment 4 
See FIG. 4 
The structural element is according to FIG. 4 and consists of low-carbon 
steel. The blank is punched from a strip, hot-worked and pressed at room 
temperature (screw 17 having a cylindrical thread as bolt-like part). The 
raw finished part is machined and galvanized. 
The dimensions are: 
lamellar part 3: W=60 mm; H=13 mm; D=4 mm 
bolt-like part 4 (17): L=12 mm; D=4.5 mm 
In the present case, the workpiece 1 corresponds to the intermediate floor 
and the workpiece 2 corresponds to the side wall of a cupboard. The former 
has a groove 6 for receiving the lamellar part 3 and the latter has a 
number of cylindrical holes for receiving the bolt-like part 4 in the form 
of a screw 17 having a cylindrical thread. Otherwise, the procedure is 
similar to Example 1. The connection is secured via the transverse hole 7 
in the intermediate floor by means of a pin and can be detached at any 
time. 
Connections between cupboard floor and cupboard side are produced in 
principle in the same way. 
The nondetachable connection between a vertical intermediate wall 
(workpiece 1 having a continuous groove 6 in the upper end face and one in 
the lower end face) and a cupboard floor or cupboard top (workpiece 2 
having cylindrical longitudinal holes 8) may be mentioned here as a 
variant of this Example. The intermediate wall is inserted horizontally 
over the lamellar parts 3 provided with "structure". Gluing is effected 
analogously to the variant in Example 2. 
Embodiment 5 
See FIG. 5 
The structural element is according to FIG. 5 and has in principle the same 
dimensions as in FIG. 4. The screw 18 having a cylindrical metal thread is 
precision machined. Otherwise, the material and production correspond to 
the data stated under Example 4. 
Similarly to Example 4, the connection here relates to the detachable 
connection of a cupboard floor to a cupboard side, especially in the form 
of a corner joint. The cupboard side is predrilled for the insertion of 
threaded dowel plugs having a cylindrical internal thread. The structural 
elements are then screwed, by means of their screw 18 having a cylindrical 
metal thread (bolt-like part 4), into the dowel plugs of the cupboard side 
(workpiece 2). The cupboard floor (workpiece 1) is provided in its end 
faces with grooves 6 for receiving the lamellar part 3 and with transverse 
holes 7 for securing by means of screws/pins. The cupboard floor is then 
pushed onto the lamellar parts 3 of the structural elements in a 
conventional manner and secured laterally via the transverse holes 7. 
A similar procedure is adopted in the case of multi-part cupboards 
assembled in a row. Instead of using dowel plugs in the cupboard sides, 
through holes are drilled and threaded sleeves having an internal thread 
are pressed in. These receive a structural element with a screw 18 as a 
bolt-like part 4 coaxially from each side. 
Embodiment 6 
See FIG. 6 
The structural element having the form according to FIG. 6 consists of 
low-carbon steel and is produced similarly to Example 1. The lamellar part 
3 is punched and the bolt-like part 4, in the form of a threaded sleeve 
19, is produced from a section of a tube having an internal thread, and 
the end face is butt-welded to the lamellar part 3. The raw finished part 
is burred, cleaned, machined, pickled and chromium-plated. The dimensions 
correspond approximately to those in Example 4. Here, the threaded sleeve 
19 has an external diameter of about 5.5 mm, and the internal thread 
corresponds to M 4. 
As in Example 5, the connection here relates to the detachable fixing of a 
cupboard floor to a cupboard side. The cupboard side (workpiece 2) is 
provided with through holes having the external diameter of the threaded 
sleeves 19 and the latter are inserted into the relevant hole and secured 
from the opposite side with a screw bolt. The cupboard floor (workpiece 1) 
is provided with grooves 6 and with transverse holes 7 according to 
Example 5 and is pushed onto the lamellar parts 3 and secured. 
A similar procedure is adopted in the case of multi-part cupboards. 
Inserted into the through holes in the cupboard side are threaded bolts 
which receive, on both sides, the threaded sleeves 19 of the opposite 
structural elements, onto whose lamellar parts 3 are pushed the cupboard 
floors lying in the same plane. 
Embodiment 7 
See FIGS. 5 and 6 
This relates to the combined use of structural elements with a screw 18 
having a cylindrical metal thread (FIG. 5) and structural elements having 
a threaded sleeve 19 (FIG. 6) of the same thread diameter, said structural 
elements forming a pair. The material, design, dimensions and production 
of the structural elements correspond to Examples 5 and 6. 
In the case of the detachable connection, the procedure adopted is similar 
to that in Example 6 for the fixing of a plurality of floors to a cupboard 
side. Holes having the size of the external diameter of the cylindrical 
threaded sleeve 19 are drilled in the cupboard side (workpiece 2), and 
said threaded sleeve is inserted and the bolt-like part of the opposite 
structural element, which part is in the form of a screw 18, is screwed in 
and secured. All other procedures correspond to those of Examples 5 and 6. 
Embodiment 8 
See FIG. 7 
The structural element formed according to FIG. 7 consists of 
chromium-plated low-carbon steel and is produced similarly to Example 1. 
The lamellar part 3 is punched and the bolt-like part 4, in this case in 
the form of pin 20, is produced from a section of a cylindrical rod and is 
butt-welded at the end face to the lamellar part 3. Deburring, cleaning, 
machining, pickling and chromium-plating correspond to the procedure in 
the preceding Examples. The dimensions of the structural element 
correspond approximately to those of Example 4. Here, the pin 20 has a 
diameter of about 5 mm. 
The present case relates to the arrangement of a shelf in a cupboard recess 
and securing to prevent falling out. Vertical rows of holes are present at 
the same height in the side wall of the cupboard. The pin 20 of the 
bolt-like part of the particular structural element is inserted into the 
hole provided in such a way that the lamellar part 3 comes to rest with 
its surface horizontal. The shelf is simply placed on the lamellar parts 3 
and if necessary secured by means of screws or pins via the holes 5 and 
the transverse holes 7 to prevent it from falling out. 
Arrangements of shelves (workpiece 1) having arc-shaped recesses in the 
lower surface of the shelf (parallel to the horizontal plane of the shelf) 
or having arc-shaped grooves 6 are considered to be variants of this 
Example. Consequently, the shelves are retained in their position in a 
better and more stable manner and also contribute to the rigidity of the 
total piece of furniture. 
The handling of the screwing tool according to FIG. 8 for mounting the 
structural element in workpiece 2 and of the drilling template according 
to FIG. 9 for producing the transverse hole 7 in the workpiece 1 is 
familiar to any person skilled in the art and requires no additional 
explanation. 
The invention is not limited to the embodiments. 
The metallic structural element for connecting workpieces 1 and 2 
consisting of wood, woodworking material, such as particle board, 
laminated board or plastic, based on the groove-and-tongue principle, 
consists of a flat lamellar part 3, which provides the non-positive 
connection to the first workpiece 1 provided with a groove 6 or a slot and 
a transverse hole 7, and a bolt-like part 4 which, through screwing or 
pinning, provides the non-positive connection to the second workpiece 2 
provided with a longitudinal hole 8 and which rests with its end face at 
right angles on the lamellar part 3 and is firmly connected to the said 
second workpiece 2, the lamellar part 3 having, in its center, along the 
axis of the bolt-part 4, a hole 5 which is at right angles to the plane of 
the lamella and intended for fixing the first workpiece 1 by means of a 
screw or of a pin. The lamellar part 3 preferably has an arc shape 9 at 
its outer end face and possesses, at its end face adjacent to the bolt, a 
projecting flat stop 10 with a recessed step 11 and, toward both tapering 
ends in the direction of the plane of the lamella, a recessed taper 12 in 
order to ensure greater convenience for screwing or insertion into the 
second workpiece. In a special embodiment, the lamellar part 3 has an arc 
shape 9 at its outer end face and also has a rectangular shape 13 so that 
the transverse dimension exceeds the dimension of the stop 10 by not more 
than 20%. 
The structural element advantageously has grooves 14 in the outer end face 
of the lamellar part 3, which grooves are intended for receiving a 
mechanical screwing tool which is provided with corresponding beads 15 in 
order to prevent lateral slipping during the screwing process. 
The bolt-like part 4 consists of a wood screw 16 having a conical thread 
for screwing into wood, particle boards or soft plastic or dowel plugs, or 
of a screw 17 having a cylindrical thread for screwing into cylindrical 
holes in wood, particle boards or plastic, or of a screw 18 having a 
cylindrical metal thread for screwing into a threaded sleeve, threaded 
dowel or nut, or of a threaded sleeve 19 provided with an internal thread 
for screwing onto a screw, threaded bolt or threaded rod, or of a pin 20 
or of a smooth tube. 
In its particular embodiment, the lamellar part 3 has lateral surfaces 
which, in order to improve the adhesion when glued to the workpiece 1, are 
roughened, possess indentations or protuberances or a structured pattern 
or are otherwise treated to increase the surface area. 
The screwing tool for the structural element consists of a cylindrical or 
polygonal shaft 21 and a head 22 having a transverse groove 23 with a 
circular bottom and lateral beads 15. 
The drilling template for the structural element consists of a member 
having a U-shaped cross-section, with a plate-like arc-shaped template 24 
corresponding to the groove shape of the first workpiece 1, a stop part 25 
for depth adjustment and a counter-plate 26 for receiving the drill bush 
27 and a cut-out 28 for monitoring and a center mark 29. 
Advantages of the Invention 
The connection between the workpieces is detachable at any time by removing 
the metallic structural element. 
If a nondetachable firm connection of the workpieces is desired, this is 
possible without changing the design and the procedure, by gluing the 
lamellar part to the grooved workpiece. 
Suitability for mass production of the structural element. 
Universal applicability of the structural element for all types of joining 
and assembling of any number of workpieces. 
No special additional tools required. A groove cutter and drill are 
sufficient for preparing the workpieces to be connected. 
Little time required for connecting the workpieces. The method is therefore 
suitable for mass production in joinery. 
Mechanically very strong connection with high load-bearing capacity and 
with minimum danger of cracking or of breaking of the material of the 
workpieces close to the connection.