Tubular drill tool

The drill tool of the present invention comprises a profiled tubular drill shank with a drill head, which consists of the free part of the drill shank with guide strips and cutting element fastened to it, characterized in that the cutting element (3) is fixed in a position pressed or forged into the drill shank (1).

The present invention relates to a drill tool for drilling deep holes, and 
comprises a drill shank and a drill head, provided with guide strips and a 
cutting element, which preferably are made of sintered carbide, ceramic or 
another hard alloy. Such drill tools are provided with one or several 
passages extending through the tool in its longitudinal direction which 
passages are used for carrying away chips. The drill tools, which are 
usually called gun drills and especially used for drill diameters between 
3-20 mm, work in the following way: Cutting medium is carried under high 
pressure in passages extending through the drill shank and drill head to 
the cutting place, whereafter the cutting medium with chips is carried 
away out of the drill hole through a profiled passage. A previously known 
drill in this field comprises a profiled, tubular shank with a compact 
drill head welded or soldered to the shank, which drill head is usually 
made of sintered carbide. 
For getting the best possible cooling of the cutting place and for 
guaranteeing good transportation of chips a great area of passages 
extending through the drill head is pursued. In this connection, there is 
a great risk that the drill head, if it is made wholly of sintered 
carbide, becomes so greatly weakened after hollowing out of passages that, 
partly, great difficulties of manufacture arise with accompanying discard 
of material due to cracking, and that the drill head can easily burst when 
used, as sintered carbide is a brittle material. A compact drill head of 
sintered carbide is unnecessarily expensive and heavy since that material 
is expensive to manufacture and has high density. Moreover, it is hard and 
time-consuming to drill a hole in such a compact body of sintered carbide. 
Furthermore, a soldering joint or weld joint between drill head and drill 
shank is a weak point, in the drill tool, and here breaking often appears 
when the drill is used. 
Yet another drawback resides in the fact that cutting insert and guide 
strips are of the same material if the drill head is wholly made of 
sintered carbide. That means that a material which has optimum 
characteristics both regarding cutting effect and wear cannot be chosen. 
As a principle, the cutting element shall be chosen with regard to its 
ability to perform a cutting work, while the material of the guide strips 
shall be chosen with regard to their ability to take up the forces which 
act on the drill head, and to minimize the wear which arises at contact 
with the bored hole.

FIGS. 1 and 2 disclose a drill, the drill shank 1 of which comprises a 
profiled tube and is therefore provided with an interior hole 2 for 
carrying cutting-medium to the drill head. The cutting element 3 comprises 
a sector-formed cutting insert of sintered carbide, which insert is 
fastened to that free part of the drill shank comprising the drill head in 
a suitable way of soldering, gluing or clamping. In the embodiment 
illustrated in FIGS. 1 and 2, the cutting element 3 and one 4 of the guide 
strips are manufactured in one piece, whereby the object of the guide 
strip 4 is to take up the tangential cutting forces acting on the cutting 
insert, which forces are directly transferred to the guide strip 4. Due to 
the fact that the cutting insert 3 and the guide strip 4 are made of a 
homogeneous piece, a drill head with great stability is obtained. This 
stability also depends on the fact that the cutting element 3 does not 
need to be hollowed out so extensively in order to attain the wished 
hole-area for the cutting head. As is said earlier the cutting element 3 
only takes up a sector and is fastened onto a tubular shank, whereby the 
desired hole-area is easy to attain. 
The main object of the other guide strip, guide 5, is to lead the drill in 
the hole correctly and to take up the resultant radial cutting force 
acting on the cutting insert. The guide 5 can be made of a homogenous 
piece of a wear-resistant hard alloy, and it can be fastened to the drill 
shank by soldering, gluing or clamping. The guide 5 can also be made of a 
hard alloy, which is squirted or sputtered on according to flame or plasma 
method or another similar known covering method. 
Guide 5 is separate from the cutting insert 3 and the first guide strip 4. 
Due to this fact, the guide 5 can be made of a special material, which has 
maximal wear-resistance. 
FIGS. 3-6 disclose other inventive embodiments where cutting insert 3 is 
made of a relatively thin, rectangular plate of sintered carbide or 
another wear-resistant hard alloy. The plate is laid in a position pressed 
or forged into the shank and fastened by soldering, gluing or clamping. 
The guide strip 4, which is separate from the cutting plate 3 and made of 
a suitable wear-resistant material, for instance sintered carbide, is 
fixed in a position pressed or forged into the shank. The other guide 
strip, guide 5, is separate both from the cutting plate 3 and from the 
first guide strip 4, and is made of a suitable wear-resistant material, 
for instance some type of sintered carbide. 
The cutting forces acting on the cutting insert can be directly transferred 
through the drill shank to the guide strips. This especially has reference 
to the greatest acting cutting force, the tangential force, which in the 
embodiments according to FIGS. 3-6 is directly transferred to the guide 
strip 4 lying under the cutting plate 3, owing to the fact that the tube 
walls 6 are in contact with each other under the insert 3. Even that part 
of the tube wall lying towards the guide strip 5 can be in contact with 
the part of the tube wall lying towards the insert 3. The parts 3, 4 and 5 
suitably can be manufactured of three different kinds of material in order 
to be able to overcome in an optimum way the different type of wear 
stresses, which can act due to the material being machined and to the 
cutting-data being used. 
FIGS. 3-6 differ from each other in that the guide strip 4 and guide 5 have 
different forms. Thereby the guide 5 can be made of a hard alloy sputtered 
or squirted onto the tube wall as in FIG. 3 or be fixed in a position 
forged or pressed into the tube wall as illustrated in FIGS. 4-6. 
FIGS. 7-9 disclose embodiments wherein the cutting insert 3 (as in the 
embodiments according to FIGS. 3-6) comprises a relatively thin plate 
which is laid in a position pressed or forged into the drill shank and is 
fastened by soldering, gluing or clamping. This construction admits an 
extremely stable fastening of the cutting insert, and minimizes the risk 
that the cutting insert might come loose. The intention with the three 
last embodiments is to provide for the need of drills where the demand for 
supplying cutting-medium is very strong. Therefore, no pressing-in of the 
tube walls is made in these cases, in order that the hole area shall not 
be diminished. Thus, in order to get the greatest hollow space the guide 
strips 4 and 5 can wholly or partially consist of thin layers of hard 
alloy applied on the drill shank, which alloy is adapted to the material 
that shall be machined. This application can be made by known methods such 
as for instance flame- or plasma coating. In this relationship the guide 
strips 4 and 5 can be composed of a continuous layer which extends along a 
substantial part of the jacket area of the tube wall, as is shown in FIG. 
9. The guide strips 4 and 5 can also be composed of homogeneous 
rectangular strips of a wear-resistant alloy and be fastened to surfaces 
plane milled or plane ground in the tube wall.