Wood or plastic drill bit, with conical reamer

Abstract

The present invention relates to a wood or plastic drill bit, particularly for railway sleepers, comprising a drilling zone configured to create a hole, a cylindrical portion (2) configured to evacuate chips, and a conical portion (3) configured to both form a cone and evacuate chips. This drill bit is particular in that it comprises at least three helical cutters, each extending continuously from the drilling zone along the cylindrical portion (2) and along the conical portion (3).

Description

[0001] The present invention relates to the field of wood or plastic drill bits. It relates to a wood or plastic drill bit with a conical reamer at the end of drilling.

[0002] Wood drill bits with a tapered reamer are used in particular for drilling railway sleepers, to create the hole for inserting lag screws. These lag screws have a taper on the part close to their head, and therefore require that the hole made also have such a taper at the entrance to the hole.

[0003] Document FR1070059 describes such a drill bit with a single drilling spiral, and two cutting edges on the conical reamer, defining a main groove in continuity with the spiral groove, and responsible for evacuating the chips from drilling, and a smaller secondary groove, contributing to the evacuation of chips from conical machining.

[0004] However, such a drill bit has the disadvantage of breaking frequently, particularly at the transition to the cone, in the event of intensive use.

[0005] Document FR2811606 describes a wood drill bit with a conical reamer, with a modified drilling area, to prevent chip jamming.

[0006] These bits all have the disadvantage of a fragile point between the cylindrical part and the conical part, which causes the bits to break, especially with intensive use.

[0007] An object of the present invention is to provide a wood or plastic drill bit with a conical reamer which makes it possible to avoid at least one of the drawbacks of the state of the art.

[0008] Another object of the present invention is to provide a wood or plastic drill bit with a conical reamer which reduces the risk of breakage, and which allows more intensive use, in particular for railway sleepers.

[0009] The present invention thus provides a wood or plastic drill bit for railway sleepers comprising a drilling zone configured to create a hole, a cylindrical part configured to evacuate the chips and a conical part, configured to both form a cone and to evacuate the chips, characterized in that it comprises at least three helical knives which each extend continuously from the drilling zone, along the part wrapped in a cylinder, and along the part wrapped in a cone.

[0010] Thanks to these provisions, the risk of breakage is reduced, which allows for more intensive use.

[0011] According to other characteristics: the ratio of the thickness of the knives to the spacing between two knives, measured at the periphery of the cylindrical part and parallel to the longitudinal axis of the cylindrical part, may be at least 1 to 2, which provides significant reinforcement of the bits, the evacuation spaces may be continuous at the transition between the cylindrical part and the conical part, which improves the reinforcement, the machined surface of the bit may have a rounding at the intersection between the cylindrical part and the conical part, so as to avoid the presence of an angle, which further improves the reinforcement of the bits, the pitch of the helical knives may be greater than half the length of the cylindrical part, which gives longer service lives, the pitch of the helical knives may be greater than the length of the cylindrical part, which gives even longer service lives,said bit may comprise exactly three helical knives, which gives particularly interesting results, the thickness of the knives in the conical part may increase less quickly in proportion to the diameter of the conical part, which also allows the bits to be reinforced, a part of the bit may be hardened, so as to increase its hardness, and another part may not be hardened, the transition zone between the cylindrical part and the conical part being in the unhardened part, thus allowing a longer life of the bit.

[0012] The present invention will be better understood upon reading the detailed description which follows, with reference to the appended figures in which: [ Fig. 1 ] There fig. 1 is a side view of a wood drill bit according to the state of the art [ Fig. 2 ] There fig. 2 is a sectional view of the wood drill bit according to the state of the art. Fig. 3 ] There fig. 3 is a side view of a wood drill bit according to the invention [ Fig. 4 ] There fig. 4 is a sectional view of the wood drill bit according to the invention. Fig. 5 ] There fig. 5 is a side view of a wood drill bit according to a second embodiment of the invention [ Fig. 6 ] There fig. 6 is a sectional view of the wood drill bit according to a second embodiment of the invention.

[0013] THE fig. 1 et 2 present a wood drill bit according to the state of the art. It shows a central threaded point 1, configured to penetrate first into the wood to be drilled, then to pull the drill bit into the material by the effect of the thread and the rotation of the drill bit, a cylindrical part 2, configured to transport the shavings from the end of the drill bit to a conical part 3, configured to form a cone at the entrance to the drilling.

[0014] Within the scope of the present invention, it is possible to provide drill bits without a central threaded point 1, which can be replaced for example by a conical end as for drill bits for drilling metal, or by a quadrangular end.

[0015] A knife has a piercing end 4, a cylindrical helix 5, and a truncated cone helix 6. A core 7 is arranged at the longitudinal axis of the bit, to ensure sufficient support and strength of the helix.

[0016] Along the circumference of the bit, the ratio of the thickness of one knife to the gap with the adjacent knife is of the order of 1 to 1.5. A thinner knife may not provide sufficient mechanical strength.

[0017] For example, for a drill bit according to the invention with a diameter of 14 mm, we can have a helix pitch of 25 mm, a knife thickness, measured parallel to the longitudinal axis of the drill bit of 10 mm, with a spacing with the following knife, measured parallel to the longitudinal axis of the drill bit of 15 mm.

[0018] There fig. 2 presents a section of the wick in its cylindrical part 2. This section presents a support 8, reaching, within a predefined clearance, the circumference of diameter D, and an evacuation space 9.

[0019] In the conical part 3, the support is provided with two blades 10 configured to machine the wall of the hole, and enlarge it. One of them is in the continuity of the knife of the cylindrical part 2, the other is added in the conical part 3, to contribute to the machining of the cone.

[0020] With such a drill bit according to the state of the art, breaks are observed at the transition between the cylindrical part 2 and the conical part 3.

[0021] Whether the knife section is increased to increase its strength, or reduced, the bits continue to break.

[0022] The inventor carried out numerous tests with different shapes of the wick.

[0023] The invention consists of adding at least one knife to have at least two in total, preferably adding two knives to have three in total.

[0024] The inventor observed that with two knives, the wicks break less, and with three knives, the result is even better.

[0025] The inventor observed this improvement by increasing or decreasing the overall section of the wick.

[0026] The wicks therefore hold better and break less, even if we have a little less evacuation volume, due to the minimal material needed to make the additional blades.

[0027] THE fig. 3 à 6 have two wood drill bits according to the invention, with two knives in the fig. 3 et 4 , with three knives in the fig. 5 et 6 . There is seen a drilling end 4, comprising, in the example shown, a central threaded point 1, configured to penetrate first into the wood to be drilled, then to pull the drill bit into the material by the effect of the thread and the rotation of the drill bit, a cylindrical part 2 configured to evacuate the chips produced by the drilling end 4, then a conical part 3, configured in the form of a conical reamer 3 to enlarge the hole, to evacuate the chips formed by this enlargement, and to evacuate the chips arriving from the cylindrical part 2.

[0028] The presence of the threaded tip 1 in the drawing is part of an exemplary embodiment. It is also possible, within the framework of the invention, to have other drilling ends, in particular conical as in drills for metals or quadrangular.

[0029] The term "cone" or "conical" is used here in a broad sense to include what would be a truncated cone, or a truncated part of a cone.

[0030] Furthermore, the expressions "cylindrical part" and "conical part" are used to express that the geometric envelope of the bit is cylindrical in the "cylindrical part", and that the geometric envelope of the bit is conical or frustoconical in the "conical part". As will be specified below, there is matter and void in this "cylindrical part" and this "conical part".

[0031] At least two knives each have a drilling end 4, a cylindrical helix 5, and a truncated conical helix 6. The helices interpenetrate, and are connected to a central shaft 7 of the drill bit.

[0032] The central shaft 7 is defined here as a part close to the longitudinal axis of the bit in which there is continuous material.

[0033] THE fig. 4 et 6 each have a section of the wick at the transition from its cylindrical part 2 to its conical part 3. This section has at least two supports 8, reaching, within a predefined clearance, the circumference of diameter D, and at least two evacuation spaces 9.

[0034] Surprisingly, it is not necessary to ensure a greater volume of evacuation spaces 9, nor a smaller volume of evacuation spaces 9, to obtain better resistance of the wicks. On the contrary, completely satisfactory results are obtained without significantly varying the total volume of the evacuation spaces 9.

[0035] The inventor observed during his numerous tests that it is preferable not to increase the speed of advance of the drill bit in the hole too much compared to the speed used with a drill bit of the state of the art. This is how we obtain a better prolonged hold of the drill bits.

[0036] In the conical part 3, the at least two supports 8 are provided with blades 10 configured to machine the wall of the hole, and enlarge it. The evacuation spaces 9 enlarge as the diameter D increases, which makes it possible to evacuate both the chips coming from the drilling end 4, and those produced by the blades 10 to form the cone.

[0037] According to a preferred embodiment of the invention, measured on the circumference of the bit, parallel to the longitudinal axis of the bit, the ratio of the thickness of a knife to the space with the adjacent knife is less than 1 / 2.

[0038] For example, for a drill bit according to the invention with a diameter of 14 mm and three knives, we can have a helix pitch of 50 mm, a knife thickness, measured on the section of the drill bit of 5 mm, with a spacing with the following knife, measured on the circumference of the drill bit, parallel to the longitudinal axis of the drill bit of 12 mm.

[0039] According to another example, for a drill bit according to the invention with a diameter of 14 mm and two knives, it is possible to have a helix pitch of 50 mm, a knife thickness, measured on the circumference of the drill bit, parallel to the longitudinal axis of the drill bit, of 8 mm, with a spacing with the following knife, measured on the circumference of the drill bit, parallel to the longitudinal axis of the drill bit, of 17 mm.

[0040] According to another example, for a drill bit according to the invention with a diameter of 14 mm and three knives, it is possible to have a helix pitch of 120 mm, a knife thickness, measured on the circumference of the drill bit, parallel to the longitudinal axis of the drill bit, of 10 mm, with a spacing with the following knife, measured on the circumference of the drill bit, parallel to the longitudinal axis of the drill bit, of 30 mm.

[0041] The inventor observed during his numerous tests that a long pitch is advantageous for improving the hold of the bits. Improved results are obtained with a pitch of at least half the length of the cylindrical part 2.

[0042] The inventor observed that even better hold of the wicks is obtained with a pitch greater than the length of the cylindrical part 2.

[0043] According to the invention, the evacuation spaces 9 are continuous at the transition between the cylindrical part 2 and the conical part 3.

[0044] According to a particular embodiment of the invention, the volume of the evacuation space 9 increases in the conical part 3.

[0045] According to a preferred embodiment of the invention, the machined surface of the bit has a rounding at the intersection between the cylindrical part 2 and the conical part 3, so as to avoid the presence of an angle.

[0046] According to a preferred embodiment of the invention, a part of the bit is hardened, so as to increase its hardness, for example up to 45 HRC, or even 55 HRC, and another part is not hardened, the transition zone between the cylindrical part and the conical part being in the unhardened part.

[0047] For example, half of the cylindrical part on the drilling area side, at the end of the drill bit is hardened, the other half of the cylindrical part, on the side of the transition zone with the conical part, is not hardened; then the first half of the conical part, on the side of the cylindrical part is not hardened, and the second half of the conical part, towards the fixing end of the drill bit is hardened.

[0048] According to this embodiment, the entire bit is not dipped, but localized dipping is carried out in certain areas, allowing other areas, such as the transition area between the cylindrical part and the conical part, not to be dipped; thus increased hardness can be given to certain areas but not to others.

[0049] The inventor observed an optimal lifespan of the bits, in particular the three-blade bits, according to this embodiment.

[0050] Although the above description is based on particular embodiments, it is in no way limiting of the scope of the invention, and modifications may be made, in particular by substitution of technical equivalents or by different combination of all or part of the characteristics developed above.

Claims

1. Wood or plastic drill bit, in particular for railway sleepers, comprising a drilling area configured to create a hole, a cylindrical part (2) configured to evacuate the chips and a conical part (3), configured to both form a cone and to evacuate the chips, characterized in that it comprises at least three helical knives which each extend continuously from the drilling zone, along the cylindrical part (2), and along the conical part (3).

2. Drill bit according to the preceding claim in which the ratio of the thickness of the knives to the spacing between two knives, measured at the periphery of the cylindrical part (2) and parallel to the longitudinal axis of the cylindrical part (2) is at least 1 to 2.

3. Wick according to one of the preceding claims, in which the discharge spaces (9) are continuous at the transition between the cylindrical part (2) and the conical part (3).

4. Drill bit according to one of the preceding claims, in which the machined surface of the drill bit has a rounding at the intersection between the cylindrical part (2) and the conical part (3), so as to avoid the presence of an angle.

5. Drill bit according to one of the preceding claims, in which the pitch of the helical knives is greater than half the length of the cylindrical part (2).

6. Drill bit according to one of the preceding claims, comprising exactly three helical knives.

7. Drill bit according to one of the preceding claims, in which the pitch of the helical knives is greater than the length of the cylindrical part (2).

8. Drill bit according to one of the preceding claims, in which the thickness of the knives in the conical part (3) increases less quickly in proportion to the diameter of the conical part (3).

9. A drill bit according to any preceding claim, wherein a portion of the drill bit is hardened, so as to increase its hardness, and another portion is not hardened, the transition zone between the cylindrical portion and the conical portion being in the unhardened portion.

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