Drilling device for producing drill holes with an undercut

A drilling device for producing drill holes with undercuts and comprising a drill bit, a drill bit holder for receiving the drill bit and having a suction chamber, and a suction bell surrounding the drill bit holder and communicating with the suction chamber therein, the stem of the drill bit having a continuous axial bore communicating with the suction chamber and a plurality of slots arranged in a region of a cross-sectional enlargement of the stem.

BACKGROUND OF THE INVENTION 
The invention relates to a drilling device for producing drill holes with 
an undercut and comprising a drill bit attached to a drill bit holder and 
a suction bell. 
German Offenlegungsschrift 33 40 090 discloses a drilling device of the 
type mentioned in which a drill bit can be screwed into a drill bit 
holder. A suction bell is provided in the region of the drill bit holder. 
The suction bell surrounds the drill bit holder and the drill bit stem. 
The suction bell is attached with a suction hose to a suction fan of a 
drilling machine or similar apparatus. The purpose of the suction device 
is to suck off the drilling dust accumulating in the drill hole during the 
drilling operation. In this known device, the drill bit stem is guided 
with a lateral play in a suction sleeve so that the drill bit is pivotable 
within the suction sleeve. The pivotal movement enables to produce the 
undercut at the bottom of the drill hole. 
Metal expansible fixing plugs can be inserted in a drill hole with an 
undercut. They expand in the region of the undercut and are, thus, 
anchored positively in the drill hole. 
To produce an undercut at the bottom of the drill hole that is as accurate 
as possible, the pivotal movement of the drill bit has to be limited. This 
can be achieved by providing in the middle of the drill bit stem a 
cross-sectional enlargement which serves as a pivot bearing that engages 
the wall of the drill hole. The cross-sectional enlargement, however, 
makes it difficult to suck off the drilling dust, since there is only a 
small gap left clear in the region of the cross-sectional enlargement for 
sucking the drilling dust away. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a drilling device for producing 
drill holes with an undercut and having a suction device which is of a 
simple construction and permits the drilling dust to be sucked away at the 
drill bit tip. The object of the invention is achieved by providing in the 
drill bit stem a continuous axial bore which opens into a suction chamber 
of the drill bit holder, and slots in the region of the cross-sectional 
enlargement of the drill bit stem. The continuous axial bore enables the 
drilling dust to be sucked away directly at the drill bit tip. The slots 
permit the volume of air sucked away to flow back. The slots additionally 
have the advantage that they prevent the drill stem from jamming in the 
drill hole. When the drilling device is provided with a smooth drill bit 
stem and a drill bit stem enlargement, which corresponds approximately to 
the diameter of the drill head, the drill bit frequently jams, as test 
drillings have shown. 
The drill bit preferably has a thread end portion with which it is screwed 
into the drill bit holder having a suction chamber surrounded by a tubular 
suction bell. The suction bell preferably includes a tube portion with a 
laterally projecting suction nozzle to which a suction hose of a suction 
pump can be attached in a manner known per se. The tube portion of the 
suction bell is held in a very simple manner between two flanges provided, 
respectively, on the drill bit holder and on the drill bit stem. The 
flange formed on the drill bit stem serves, at the same time, as a stop 
that determine the maximum depth of the drill hole. 
The slots formed on the drill bit stem, are about 1 to 2 cm long and, 
preferably, have a pitch such that they convey the drilling dust 
accumulating in this region towards the drill head. The pitch of the slots 
may, alternatively, however, be such that the slots alternate opposite to 
each other or are of the same shape, as in the case of drilling dust 
grooves, if this is required for special applications. The slots serve 
both as air inlet channels and also for further transport of the drilling 
dust accumulating in this region. 
To mount the drill plate in the drill head in an optimum manner, it is 
advantageous to extend the continuous bore laterally past the drill plate 
at a distance therefrom. The drill plate can thus be inserted in a groove 
provided in the solid part of the drill head. 
It is especially advantageous to branch the continuous bore in the region 
of the drill head, so that on each side of the drill plate a branch of the 
continuous bore leads to a suction opening. This can also be regarded as a 
forking of the continuous bore. The two suction openings obtained thereby 
permit the accumulated drilling dust to be sucked away directly on both 
sides of the drill plate. 
The present invention both as to its construction so to its mode of 
operation, together with additional objects and advantages thereof, will 
be best understood from the following description of the preferred 
embodiment with reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The drilling device of the present invention comprises a drill bit holder 
1, a drill bit 2, and a suction bell 3. The drill bit holder 1 has a 
mounting shank 4 with which it can be clamped in a drill chuck or similar 
part of a drilling machine. In addition, the drill bit holder 1 has a 
suction chamber 5 onto which the suction bell 3 can be pushed from 
beneath. An opening 6 connects the suction chamber 5 with the inner 
chamber 7 of the suction bell 3. 
A bore 8 which is provided at the lower end of the drill bit holder 1 and 
forms the suction chamber, has an internal thread 9 shown in FIG. 2. 
The drill bit 2 has a threaded end portion 10 with which it can be screwed 
into the internal thread 9. Prior to this, however, the suction bell 3 is 
pushed over the suction chamber 5. A flange 11 formed on the drill bit 
holder 1, and a flange 12 formed on the drill bit 2, close the suction 
bell 3 at its two end faces. 
The drill bit 2 comprises a smooth stem 13 provided with slots 14 
distributed around its periphery. The slots 14 are located in a region 
where the cross-section of the stem is greatest, and serve as external air 
channels and as reaming elements which prevent the drill bit from becoming 
jammed in the drill hole. The slots 14 could also be arranged to extend at 
an acute angle relative to the longitudinal axis of the drill bit as shown 
in FIG. 4. The slots may have a pitch corresponding to the pitch drilling 
dust grooves. The grooves can, however, also have a pitch such that the 
drilling dust accumulating in this region, is conveyed in the direction of 
the drill head 15. 
The drill bit 2 has a continuous axial bore 16 shown in the drawing by 
broken lines. The continuous bore 16 has its smallest diameter in the 
region of the drill head 15 and adjacent to the drill head region, where 
the diameter of the stem is smallest. In the region where the 
cross-section of the stem widens, the continuous bore 16 likewise has a 
larger diameter, whereby a considerable improvement in the suction of the 
drilling dust is achieved. The suction chamber 5 has a diameter larger 
than the larger diameter of the bore 16, and opens into the suction bell 3 
by means of openings 6. Thus, the suction bore has a flow cross-section 
that increases continuously from the drill head tip. This results in 
optimum suction of the drilling dust. 
The suction bell 3 has a laterally projecting suction nozzle 17 to which a 
suction hose (not shown) of a suction pump can be attached in a manner 
known per se. 
Lateral cutting edges 18, 19 of a drill plate 20 which project laterally 
from the drill head 15, serve to produce an undercut in a drill hole. The 
maximum drill head diameter is determined by the lateral cutting edges 18, 
19. The maximum drill head diameter is only slightly larger than the 
maximum cross-sectional enlargement in the region 21 of the drill stem. 
The cross-sectional enlargement of the drill stem serves as a pivot 
bearing, which provides for a predetermined swinging of the drill head 15 
at the bottom of the drill hole to form an undercut. As it can be seen in 
FIG. 5, the tapering surface extending from the cross-sectional 
enlargement of the bit stem limits (defines) the size of the undercut. The 
enlarged region 21 engages the drill hole wall during this operation. 
FIG. 3a shows the drill bit 2 in the region of the drill head 15. The 
continuous bore 16 forks and extends to suction openings 22 formed on both 
sides of the drill plate 20 mounted at the front end of the drill head 15. 
For this purpose, inside the drill head 15, straight channels 23 are 
formed. The channels converge in the drill stem. 
The drill head 15 shown in FIG. 3 , flares conically. However, it is also 
possible to form the drill head as a straight shank part, as shown in FIG. 
1. In the case of the conically flared drill head, it is possible, 
however, to provide larger suction openings 22 than in a straight drill 
head of a smaller diameter. 
While the invention has been illustrated and described as embodied in a 
drilling device for producing drill holes, with an undercut, it is not 
intended to be limited to the details shown, since various modifications 
and structural changes may be made without departing in any way from the 
spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention. 
What is claimed as new and desired to be protected by Letters Patent is set 
forth in the appended claims.