Drilling tool of the loose top type
A drilling tool of the loose top type includes a basic body having two bendable branches having inner support surfaces that are resiliently pressable against side contact surfaces of a replaceable loose top. The mounting of the loose top is affected by turning-in from an initial position to an operative end position. An abutting edge along each side contact surface then bends out the branches and subjects the branches to a spring force that reaches a maximum in a dead position so as to then decrease somewhat up to the operative end position. During the final phase of the rotary motion, the operator obtains, in a tactile and/or auditory way, confirmation of the loose top indeed reaching its operative end position.
1. Drilling tool for chip removing machining, comprising:
a basic body having front and rear ends, between which a first center axis extends around which the basic body is rotatable in a given direction of rotation, and
a loose top having front and rear ends, between which a second center axis extends, the front end of the loose top including one or more cutting edges,
wherein the front end of the basic body comprises a jaw between two axially protruding, peripherally situated branches that are elastically bendable, the branches are capable of resiliently clamping the loose top in the jaw by inner support surfaces of the branches being resiliently pressed against external side contact surfaces of the loose top, and capable of transferring torque to the loose top via tangential support surfaces of the branches and cooperating tangential contact surfaces of the loose top,
wherein the inner support surface of each of the individual branches extends between first and second tangentially separated side borderlines, the first tangentially separated side borderline is heading and the second tangentially separated side borderline is trailing during rotation of the tool,
wherein each external side contact surface of the loose top extends between first and second side borderlines, the second side borderline rotationally trailing the first side borderline and is included in an edge to a trailing part surface, besides which the loose top is axially insertable into the jaw and turnable into and out of an operative engagement with the branches,
wherein a second imaginary diametrical line, which extends perpendicular to the second center axis of the loose top between abutting edges that abut the second side borderline of each of the external side contact surfaces, has a length that is greater than the length of an analogous first diametrical line, which extends a shortest possible distance between the inner support surfaces when the branches are unloaded, and has opposite end points located at tangential distances from the first tangentially separated side borderline and the second tangentially separated side borderline of the respective inner support surface in such a way that upon a turning-in operation of the loose top into engagement with the branches a successively increasing deflection of the branches is provided by the edges up to a predetermined intermediate position of maximum clamping force, so as to then decrease during the continued turning of the loose top until an end position is reached, and during the final phase of the rotary motion between the intermediate position and the end position, the clamping force in the branches assists in bringing the loose top to the end position.
2. The drilling tool according to claim 1 , wherein a first, shortest diametrical line between the inner support surfaces of the branches has end points located nearer the second tangentially separated side borderlines of the inner support surfaces than the first tangentially separated side borderlines.
3. The drilling tool according to claim 1 , wherein the external side contact surfaces of the loose top, via intermediate surfaces, transform into a pair of external guide surfaces being axially behind, which have a rotationally symmetrical shape that is defined by a second imaginary circle, the diameter of which is less than the length of the second diametrical line, and
wherein the branches include a pair of cooperating internal guide surfaces, which are situated axially behind the inner support surfaces, and have a rotationally symmetrical shape that is defined by a first imaginary circle, the diameter of which is greater than the diameter of the second imaginary circle, and smaller than the length of the first diametrical line.
4. The drilling tool according to claim 3 , wherein the internal and external guide surfaces are cylindrical and concentric with the first and second center axes of the loose top and of the basic body, respectively.
5. The drilling tool according to claim 1 , wherein each external side contact surface of the loose top is at least partially plane and forms an acute angle (β) with said second diametrical line through the loose top, besides which the cooperating inner support surface of the respective branch is plane and capable of providing surface contact between the pairs of side contact surfaces and inner support surfaces.
6. The drilling tool according to claim 1 , wherein the individual side contact surface includes two contact surface sections, wherein the first contact surface section is rotationally trailing the second contact surface section and includes said abutting edge, the second contact surface section being cross-sectionally convexly arched in order to cooperate with a concavely arched, second support surface section, which is included in the inner support surface of the individual branch together with a rotationally trailing, first support surface section.
7. The drilling tool according to claim 6 , wherein the second contact surface section of the side contact surface of the loose top and the second support surface section of the inner support surface of the branch have a part-cylindrical shape.
8. The drilling tool according to claim 5 , wherein the acute angle (β) between the second diametrical line and the individual side contact surface amounts to at most about 88°.
9. The drilling tool according to claim 5 , wherein the acute angle (β) amounts to at least about 75°.
10. The drilling tool according to claim 5 , wherein the acute angle (β) is from about 80° to about 86°.
11. The drilling tool according to claim 5 , wherein the external side contact surfaces of the loose top each diverge at a certain angle of divergence (α) in a direction from the rear end of the loose top toward the front end of the loose top.
12. The drilling tool according to claim 11 , wherein the angle of divergence (α) amounts to at least about 0.20°.
13. The drilling tool according to claim 11 , wherein the angle of divergence (α) amounts to at most about 3°.
14. The drilling tool according to claim 11 , wherein the angle of divergence (α) is from about 0.60° to about 1.20°.
15. The drilling tool according to claim 1 , wherein the inner support surfaces of the branches run parallel to each other and to the first center axis of the basic body when the branches are unloaded.
16. The drilling tool according to claim 1 , wherein the abutting edge along each external side contact surface of the loose top is straight.
17. The drilling tool according to claim 1 , wherein the individual abutting edge along each side contact surface is in the form of a radius transition between the side contact surface and a trailing part surface.
18. The drilling tool according to claim 1 , wherein each external side contact surface of the loose top and the trailing part surface, which meets the side contact surface along the abutting edge, form an obtuse angle (γ) with each other.
19. The drilling tool according to claim 1 , wherein the external side contact surfaces extend rearward from at least one clearance surface that is included in the front end of the loose top and rotationally trails one of the cutting edges.
20. The drilling tool according to claim 1 , wherein the basic body and the loose top comprise cooperating locking elements in order to counteract unintentional axial retraction of the loose top out of the jaw.
21. The drilling tool according to claim 20 , wherein the locking elements include a seat, which is recessed in a rear end of the individual branch and into which a male member situated adjacent to an axial contact surface of the loose top is insertable.
22. The drilling tool according to claim 21 , wherein the seat is a chute situated behind the tangential support surface of the branch, and the male member is a ridge situated behind a tangential contact surface of the loose top.
23. The drilling tool according to claim 1 , wherein the rear end of the loose top is plane and without a centering pin.