screw

Abstract

The invention relates to a screw (1) with a standing milling cutter (7). In order to reduce the screw-in resistance of the screw (1), the invention proposes that the standing milling cutter (7) has two groups (9, 11) of milling ribs (10, 12) arranged one after the other, the front milling ribs (10) being counter to the screw thread (8) and the rear milling ribs (10) being parallel to the screw thread (8). The two groups (9, 11) of milling ribs (10, 12) have a greater pitch than the screw thread (8) in terms of value, and the milling ribs (10, 12) transition into one another in a V shape.

Description

Technical Field

[0001] This invention relates to a screw comprising: a screw head; a screw shank adjacent to the screw head; and a screw tip abutting the front end of the screw shank; a screw thread extending over a portion of the length of the screw shank and having a pitch; and an end mill disposed between the screw thread and the screw head, the end mill having a first set of milling ribs arranged helically on its outer periphery, the first milling ribs having a first pitch, wherein the first pitch is different from the thread pitch. In particular, this invention relates to a self-tapping screw in which mating threads in the material itself (e.g., wood or plastic) are tangent to the thread of the self-tapping screw. Background Technology

[0002] Patent EP 2 326 848 B1 discloses a self-tapping screw having a screw shank, a screw head at the rear end of the screw shank, a tapered screw tip at the front end of the screw shank, and a screw thread that begins at the front end of the screw tip and extends approximately to the longitudinal center of the screw shank. Furthermore, the screw also has an end mill located between the screw thread and the screw head, the end mill consisting of a plurality of helically arranged milling ribs. The task of the milling ribs is to up-mill and widen the screw hole created by the screw, thereby allowing the unthreaded portion of the shank adjacent to the end mill to penetrate into the threaded hole, and thereby minimizing the screw-in resistance caused by friction between the workpiece and the unthreaded portion of the shank. Summary of the Invention

[0003] The objective of this invention is to provide a screw in which the screwing torque is reduced without reducing the holding value (Haltewerte).

[0004] According to the invention, this task is solved by the following feature: the end mill has a second set of milling ribs arranged helically on its outer periphery, the second milling ribs having a second pitch, wherein the second pitch is different from the first pitch and the thread pitch, wherein the first milling ribs are in the same direction as the screw thread, and the second milling ribs are in the opposite direction to the screw thread. The screw according to the invention has a screw head and a screw shank adjacent to the screw head, and a screw tip adjacent to the front end of the screw shank. Furthermore, the screw has a screw thread, which can be single-started or multi-started and extends from the screw tip along a portion of the length of the screw shank, wherein a portion of the screw tip can also be unthreaded. The screw thread has a thread pitch, wherein this thread pitch is substantially constant over the entire length of the shank region, but can deviate in the region of the screw tip. "Substantially" includes, and is also included hereinafter, deviations of + / -20%, and especially + / -10%. The term "screw tip" here does not refer to the very foremost point of the screw, but rather to the transition area, particularly the tapered section, extending from the foremost point to the screw shank. "From the screw tip" means that the screw thread can begin at the foremost end, at the very foremost point, or at the rear end (i.e., at the transition leading to the screw shank), or somewhere in between. "Foremost" and "rear" here always refer to the screwing direction. Furthermore, if the "screw shank" is mentioned, it should always be understood that the screw thread is not part of the screw shank. The same applies to the screw tip. The screw tip does not necessarily end in a point; it can also have, for example, a truncated cone shape.

[0005] An end mill is arranged at the screw shank between the screw thread and the screw head. The end mill has a first set of first milling ribs and a second set of second milling ribs. Both the first and second milling ribs are arranged spirally on the outer periphery, with the same spacing between them. The first milling ribs have a first pitch, and the second milling ribs have a second pitch, both different from the thread pitch. Furthermore, according to the invention, the first pitch and the second pitch are different. In particular, the first and second pitches are substantially constant along the longitudinal axis of the screw, respectively. If they are not constant, they refer to the average pitch, respectively.

[0006] However, according to the invention, there may also be a transition region where the first pitch transitions into the second pitch. For example, a first milling rib having a first pitch approximately four times the thread pitch can transition arcuately into a second milling rib that extends parallel to the screw's longitudinal axis, i.e., the second milling rib has an infinite second pitch. Between the first and second pitches, the milling rib has an intermediate pitch. In this particular example according to the invention, the "spiral" shape for the second milling rib refers to the shape of a spiral with an infinite pitch.

[0007] A set of milled ribs typically extends along the same length along the longitudinal axis of the screw. A set typically consists of at least two, and preferably three or four, milled ribs, but implementations with only a single milled rib are also possible.

[0008] The milling ribs mentioned above, arranged according to the invention, achieve better separation of the wood fibers, in particular, from the surrounding screw holes, and thus more efficient milling, compared to what has been disclosed to date in the prior art. The wood fibers are at very different angles to the longitudinal axis of the screw. Therefore, the milling ribs of the front group only cut a portion of the relevant wood fibers, while another portion of the wood fibers is only squeezed to the hole wall, i.e., the wall of the screw hole. Due to the different pitch of the rear milling ribs, at least a portion of these remaining wood fibers are realigned and similarly cut. Thus, with the mutual cooperation of the milling ribs, better milling results are achieved, thereby reducing the screw-in torque.

[0009] Preferably, the first milled rib is in the same direction as the screw thread, and the second milled rib is in the opposite direction to the screw thread. This achieves the aforementioned effect particularly well. "In the same direction" and "in opposite direction" refer to the orientation in the circumferential direction around the screw's longitudinal axis. Specifically, the first milled rib is closer to the screw thread than the second milled rib. In other words, at the screw shank, the first milled rib is positioned further forward than the second milled rib.

[0010] To reliably achieve the desired milling effect, this invention proposes that the values ​​of the first and second pitches are greater than the thread pitch, and in particular, at least twice the thread pitch. Here, a right-hand thread, or one with milling ribs oriented in the same direction as the right-hand thread, is understood as a thread with a positive pitch, while a left-hand thread is understood as a thread with a negative pitch. It has been shown that when the pitch value is greater than the thread pitch, the described effect works better during milling. However, in particular, the value is at most ten times the thread pitch. The effect deteriorates when the pitch is even larger.

[0011] Preferably, the values ​​of the first and second pitches are substantially the same, which has a beneficial effect on material flow and the forces acting, especially when roll forming end mills.

[0012] Two sets of milled ribs can be arranged spaced apart from each other at the rod, but are preferably arranged directly adjacent to each other, i.e., directly successive. This avoids chip accumulation between the sets, which would increase the screwing torque. Furthermore, the invention proposes that the first milled rib transition into the second milled rib, provided that both sets have the same number of milled ribs. This not only results in a visually appealing geometry but also facilitates manufacturing, especially by roll forming, because fewer edges need to be constructed compared to the circumferential misalignment of the milled ribs, thus facilitating material flow during forming.

[0013] Preferably, the milled ribs of the front group run in the opposite direction to the screw thread, while the milled ribs of the rear group run in the same direction as the screw thread, with the first milled rib transitioning into the second milled rib. This creates a V-shape with milled ribs serving as arms of the V. This V-shape points circumferentially, more precisely, in the direction in which the screw must rotate to be screwed in. Therefore, the milled ribs clearly define the screw-in direction, which improves operation, especially when the operator is inexperienced. In particular, this clear screw-in direction is highly advantageous if the screw thread is to be left-handed (which is uncommon).

[0014] In a preferred embodiment, the outer diameter of the end mill is smaller than the outer diameter of the screw thread, but larger than the shank diameter. This ensures that the screw hole in the base is not enlarged beyond what is necessary, thus avoiding unnecessary increases in the screwing torque. "Outer diameter" refers to the diameter of the imaginary, external end mill or the cylindrical shape of the screw thread, where the imaginary cylindrical shape is coaxial with the screw's longitudinal axis.

[0015] Preferably, the first milling rib extends along the longitudinal axis of the screw, the length of which corresponds to 0.6 to 1.4 times, particularly 0.8 to 1.2 times, the outer diameter of the end mill. Furthermore, in particular, the second milling rib extends for substantially the same length. Since the milling ribs are relatively short compared to known end mills, the combination of the first and second milling ribs according to the invention is also not too long, i.e., it is particularly suitable for screws with small positions between the screw thread and the screw head. Nevertheless, the relatively short milling ribs still achieve the desired effect. The end mill as a whole extends at most 3.5 times the outer diameter of the end mill.

[0016] In a preferred embodiment, a set of milled ribs extends only on a portion of the outer periphery of the screw shank to achieve good milling results. This is particularly accompanied by the previously mentioned, preferred values ​​for the pitch and length of the milled ribs, but these are also independently effective.

[0017] In principle, any number of other milling ribs can be added besides the first and second groups, provided the screw rod provides the position. However, it is preferred that at most one more group of milling ribs be provided. This third group of milling ribs, arranged spirally in a circumferential manner, has a third pitch. Here, the third pitch is also different from the thread pitch and also different from the milling ribs of the adjacent group, which, depending on the order of the group arrangement, is the first or second group. In particular, the third pitch is the same as the pitch of another group of milling ribs, that is, the pitch of the next group of milling ribs. In other words, in the case of three groups, the pitch of the preceding group is repeated in the following group. This has proven to be beneficial to the milling effect mentioned above, and also produces a particularly harmonious picture. In particular, the groups are arranged in the order of "first, second, third group", with the first and third groups in the opposite direction to the thread and the second group in the same direction as the thread, wherein the pitches of the three groups are numerically the same. Alternatively, the pitch can increase, for example, from front to back.

[0018] Especially for longer screws, this invention proposes to arrange a cylindrical bar section between the screw head and the end mill.

[0019] The features and combinations of features, embodiments, and configurations of the present invention mentioned above in the specification, as well as the features and combinations of features mentioned and / or drawn in the accompanying drawings, can be used not only in the corresponding given or drawn combinations, but also in virtually any other combination or individually. Embodiments of the present invention may not have all the features of a dependent claim. A single feature of a claim may also be replaced by another disclosed feature or combination of features. It is possible for the present invention to have, in principle, any portion of the features of an embodiment that does not have all the features of the embodiments, but rather the feature portions of the embodiments, combined with one, several, or all features of one or more other embodiments, if necessary. Attached Figure Description

[0020] The present invention will now be described with reference to two embodiments.

[0021] It shows:

[0022] Figure 1 Side view of the first embodiment;

[0023] Figure 2 Side view of the second embodiment. Detailed Implementation

[0024] exist Figure 1The screw 1 shown, according to the invention, extends along the screw's longitudinal axis A and has a screw head 2 at its rear end along the screwing direction E. This screw head has an invisible tool-receiving geometry and a biconical underside 3 pointing forward. A screw shank 4 abuts the screw head 2, transitioning into a screw tip 5 at the front end of the screw 1. In the region adjacent to the screw head 2, the screw shank 4 has a cylindrical shank segment 6 and an adjacent end mill 7. Directly in front of the end mill 7, the screw shank 4 has a screw thread 8 with a thread pitch. The thread pitch corresponds approximately 0.75 times the outer diameter DS of the cylindrical shank segment 6, and the thread outer diameter DG corresponds approximately 1.4 times the outer diameter DS of the cylindrical shank segment 6. The screw thread 8 extends continuously to the front end of the screw tip 5.

[0025] The end mill 7 has a first set of 9 first milling ribs 10 at the front and a second set of 11 second milling ribs 12 directly adjacent to it at the rear. Each set of 9, 11 has three milling ribs 10, 12, which extend spirally along the screw shank 4 at equal intervals on the outer periphery. That is, the milling ribs 10, 12 are offset from each other by 120 degrees in cross-section. The first milling rib 10 has a first pitch, which corresponds to approximately negative 4.4 times the thread pitch, i.e., the first milling rib 10 is opposite to the screw thread 8. Although the second milling rib 12 has the same pitch as the first milling rib 10 in numerical terms, it is in the same direction as the screw thread 8. Here, the first milling rib 10 transitions into the second milling rib 12 in a V-shape, and thus shows how the screw 1 needs to be screwed in. The end mill 7 has an outer diameter DF, which is approximately 15% larger than the outer diameter DS of the cylindrical shank segment 6. The first and second groups 9 and 11 have milling ribs 10 and 12 with lengths L1 and L2 along the longitudinal axis A of the screw, respectively, which approximately correspond to the outer diameter DF of the end mill 7.

[0026] When screw 1 is screwed into a base (not shown), for example, made of wood, thread 8 cuts into the base, forming a mating thread and creating a position for screw shank 4. In this case, additional geometry in the area of ​​screw thread 8, such as a secondary thread, additional edges, and the like (not shown), simplifies the screwing process by additionally separating, separating, and / or removing the material of the base from screw 1. However, if a portion of screw shank 4 penetrates into the base adjacent to screw thread 8, more material of the base needs to be extruded radially (about the longitudinal axis A of the screw) because the inner diameter DK of the screw thread is smaller than the outer diameter DS of the cylindrical shank segment 6. This is greatly simplified by end mill 1, allowing the cylindrical shank segment 6 to find sufficient position and generating almost no additional screwing resistance. In the case of wood, the first milling rib 10 cuts off a portion of the fiber, but, depending on the direction the fiber was previously facing, laterally compresses another portion of the fiber against the wall of the hole created by screwing in screw 1. The second milling rib 12 aligns and cuts the fibers that are laterally pressed to the hole wall, thereby milling away at least a larger portion of the fibers, or better milling out the screw hole, compared to the prior art, which ultimately facilitates the screw 1 being screwed in.

[0027] Figure 2 The second embodiment is shown. The screw 1a according to the invention is identical to the first embodiment in many features; therefore, to avoid repetition, only the differences are discussed. The end mill 7 is longer than in the first embodiment, and the cylindrical shank segment 6 is correspondingly shorter. In addition to the unchanged first and second groups 10, 12 milling ribs 9, 11, there is a third group 13, the third milling rib 14. This third group 13 has the same geometry as the first group 11, and the third milling rib 14 transitions V-shaped into the second milling rib 12. That is, the third milling rib 14 has the same pitch and the same length as the first milling rib 10. In the case of some woods, the third group 13 produces a smaller screw-in torque than in the first embodiment because more fibers are cut, thus milling the screw hole more effectively.

[0028] List of reference numerals

[0029] screw

[0030] 1.1a Screw

[0031] 2. Screw head

[0032] 3. Lower side of the head

[0033] 4. 4a Screw Rod

[0034] 5. Screw tip

[0035] 6. 6a Columnar rod section

[0036] 7.7a End Mill

[0037] 8. Screw threads

[0038] 9. First group of milled ribs

[0039] 10 First milling rib

[0040] 11 Second group of milled ribs

[0041] 12 Second milling rib

[0042] 13 Third group of milled ribs

[0043] 14 Third milling rib

[0044] A. Screw longitudinal axis

[0045] E. Screwing direction

[0046] DF end mills 7 and 7a outer diameter

[0047] DG screw thread 8 outer diameter

[0048] DK screw thread 8 inner diameter

[0049] The outer diameter of the DS cylindrical rod sections 6 and 6a

[0050] L1 Length of the first group of 9 milled ribs

[0051] L2 Length of the second group of 11 milled ribs

Claims

1. A screw, which has the following characteristics: - Screw head (2). - The screw shank (4, 4a) adjacent to the screw head (2), and - Screw tip (5), the screw tip being adjacent to the front end of the screw shank (4, 4a), - Screw thread (8), the screw thread extending over a portion of the length of the screw shank (4, 4a) and having a thread pitch, and - An end mill (7, 7a) disposed between the screw thread (8) and the screw head (2), the end mill having a first set (9) of first milling ribs (10) arranged helically on the outer periphery, the first milling ribs having a first pitch, wherein, The first pitch is different from the thread pitch. The end mill (7, 7a) is characterized in that it has a second set (11) of second milling ribs (12) arranged spirally on the outer periphery, the second milling ribs having a second pitch, wherein the second pitch is different from the first pitch and the thread pitch, wherein the first milling rib (10) is in the same direction as the screw thread (8), and the second milling rib (12) is in the opposite direction to the screw thread (8).

2. The screw according to claim 1, characterized in that, The values ​​of the first and second pitches are greater than the thread pitch.

3. The screw according to claim 1 or 2, characterized in that, The values ​​of the first and second pitches are substantially the same.

4. The screw according to claim 1 or 2, characterized in that, The first group (9) and the second group (11) are arranged directly and successively.

5. The screw according to claim 4, characterized in that, The first set (9) in front of the screw (1, 1a) along the screwing direction (E) is opposite to the screw thread (8), and the second set (11) behind is in the same direction as the screw thread (8), and the first milling rib (10) transitions into the second milling rib (12).

6. The screw according to claim 1 or 2, characterized in that, The first milling rib (10) extends along a length (L1) along the longitudinal axis (A) of the screw, the length of which corresponds to 0.6 to 1.4 times the outer diameter (DF) of the end mill (7, 7a).

7. The screw according to claim 1 or 2, characterized in that, At least one set of milled ribs extends only on a portion of the outer periphery of the screw rod (4, 4a).

8. The screw according to claim 1 or 2, characterized in that, The end mill (7a) has a third set (13) of third milling ribs (14) arranged spirally on the outer periphery, the third milling ribs having a third pitch, wherein the third pitch is different from the thread pitch and the adjacent set of milling ribs arranged spirally on the outer periphery.

9. The screw according to claim 1 or 2, characterized in that, A cylindrical bar section (6, 6a) is arranged between the screw head (2) and the end mill (7, 7a).

10. The screw according to claim 2, characterized in that, The values ​​of the first and second pitches are at least twice the thread pitch.

11. The screw according to claim 4, characterized in that, The first milling rib (10) transitions into the second milling rib (12).

12. The screw according to claim 6, characterized in that, The length corresponds to 0.8 to 1.2 times the outer diameter (DF) of the end mill (7, 7a).

13. The screw according to claim 8, characterized in that, The third pitch is the same as the pitch of another set of milling ribs arranged spirally on the outer periphery.

Images