Boring or penetrating the earth – Bit or bit element – Nonsymmetrical bit
Patent
1998-02-04
2000-03-07
Bagnell, David
Boring or penetrating the earth
Bit or bit element
Nonsymmetrical bit
175397, 1754201, 175427, 408223, 408227, 408230, E21B 1000
Patent
active
060327502
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a drilling tool with a drill head having an end face which is directed in the feed direction and which face has a main bit forming a drill point located on the drill axis and which bit is inclined in substantially a roof-shaped manner on either side, and the head has drilling dust grooves.
For example German patents 43 38 677 and 35 00 202 disclose drilling tools with a main bit which extends over the entire drill head of the drilling tool determine the hole diameter and which bit is constructed in a radially and axially symmetrical manner as a cutting element. Such drilling tools give an unsatisfactory drilling rate and/or require high force expenditure. In addition, a symmetrical cutting edge construction can give rise to transverse vibrations, which can lead to a geometrically non-uniform hole shape.
SUMMARY OF THE INVENTION
The problem which is being solved by the invention is to provide a drilling tool of the aforementioned type which tool permits the obtaining of a higher drilling rate and circular holes.
According to the invention this problem is solved in that the main bit has a primary cutting edge extending radially over at least one side of the main bit and a secondary cutting edge extending radially substantially over the remaining length of the main bit and which secondary cutting edge is axially set back with respect to the primary cutting edge counter to the feed direction by at least the amount of drilling feed in millimeters per revolution.
Advantageously the axial displacement of the secondary cutting edge with respect to the primary cutting edge is chosen as a function of the material characteristics of the material to be drilled. The secondary cutting edge is advantageously set back by approximately 0.3 to 1.5 mm relative to the primary cutting edge.
Preferably the length of the secondary cutting edge is chosen as a function of the material characteristics of the material to be drilled.
Additionally the drilling tool can have at least one additional cutting element.
According to a special embodiment of the invention, the two sides of the main bit emanating from the drill tip can have different lengths, with the long side extending beyond the circumferential contour of the body, the primary cutting edge extending radially over at least the long side of the main bit and the secondary cutting edge extending radially over substantially the remaining length of the main bit. The drilling tool has at least two additional cutting edges, which are arranged substantially symmetrically under an angle to the main cutting edge axis, whose cutting axes intersect the main cutting edge axis on the drill axis of the drill head and whose radially outer ends are located on the same rotation circle as the radially outer end of the primary cutting edge and together define the nominal drilled diameter, whilst the radially outer end of the secondary cutting edge is moved radially inward. The additional cutting edges over at least part of their cutting lengths are set back in the feed direction from the primary cutting edge and extend ahead of the secondary cutting edge in the feed direction.
The radially outer end of the short side of the main bit with the secondary cutting edge projects over and beyond the circumferential contour of the body.
The radially outer end of the short side of the main bit with the secondary cutting edge may not project beyond the circumferential contour of the body.
In particular, the radially outer end of the short side of the main bit with the secondary cutting edge is drawn radially inwards from the circumferential contour of the body.
Preferably the primary cutting edge extends over 5/8 to 3/4 of the nominal drilled diameter.
The angle between the additional cutting edge and the main bit is preferably 20 to 70.degree..
In addition, the angle (.alpha.) between the additional cutting edge and the main bit is chosen as a function of the drilling dust volume obtained.
Drilling dust grooves can be positioned upstream o
REFERENCES:
patent: 2567084 (1951-09-01), Stokes
patent: 2673714 (1954-03-01), Hargrave
patent: 4727946 (1988-03-01), Barr et al.
patent: 4787464 (1988-11-01), Ojanen
patent: 4951761 (1990-08-01), Peetz et al.
patent: 4967855 (1990-11-01), Moser
patent: 5314272 (1994-05-01), Kubota
Kersten Heinrich
Precht Hartmut
Bagnell David
Gebrueder Heller Dinklage GmbH
Lee Jong-Suk
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