Tandem Hob

Abstract

Makes it easier to attach the two hobs. [Solution] The tandem hob comprises a first hob including a plurality of first cutters positioned at intervals on a first helix centered on a first central axis, a second hob including a plurality of second cutters positioned at intervals on a second helix centered on a second central axis, and a collar connecting the first hob and the second hob such that the first central axis and the second central axis lie on a common axis. When the first hob and the second hob are connected by the collar, the first cutter includes a first cutting edge having its tip on the first side in the circumferential direction around the common axis. The second cutter includes a second cutting edge having its tip on the second side opposite to the first side in the circumferential direction around the common axis. The first hob and the second hob are restricted from relative rotation around the common axis and from approaching each other along the common axis.

Description

Technical Field

[0001] This disclosure relates to tandem hobs.

Background Art

[0002] When cutting gears with a hob, burrs are generated on the teeth of the gear. As one method for removing these burrs, a method using two hobs with opposite rotational directions is known (Patent Document 1). In this method, the two hobs are attached to the same shaft member of the hob machine. After cutting the gear with one hob, the shaft member is moved axially so that the cutting edge of the other hob aligns with the groove of the tooth formed on the gear. The shaft member is rotated in the reverse direction, and the gear is cut with the other hob. By cutting from both directions, the generation of burrs can be suppressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] To perform machining using two hobs, the relative positions of the two hobs must be determined. However, conventionally, the two hobs had to be attached to the shaft member one by one, and it was necessary to determine the relative positions of the two hobs on the shaft member during attachment. Since accuracy is required for hob positioning, the attachment of the two hobs was complicated.

[0005] This disclosure has been made in consideration of the above points, and an object thereof is to facilitate the attachment of two hobs.

Means for Solving the Problems

[0006] A tandem hob according to an embodiment of this disclosure is A first hob including a plurality of first cutters positioned at intervals on a first spiral centered on a first central axis, A second hob including multiple second cutters positioned at intervals on a second spiral centered on a second central axis, A collar connecting the first hob and the second hob, such that the first central axis and the second central axis are located on a common axis, In the state in which the first hob and the second hob are connected by the collar, The first cutter includes a cutting edge having its tip on the first side in the circumferential direction centered on the common axis, The second cutter includes a cutting edge having its tip on the second side opposite to the first side in the circumferential direction with respect to the common axis, The first hob and the second hob are restricted from relative rotation about the common axis and from approaching each other along the common axis. [Effects of the Invention]

[0007] According to this disclosure, the installation of the tandem hob can be facilitated. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a diagram illustrating one embodiment, and is a side view showing an example of a tandem hob. [Figure 2] Figure 2 is a side view of the tandem hob shown in Figure 1, but disassembled. [Figure 3] Figure 3 is a disassembled perspective view of the tandem hob shown in Figure 1. [Figure 4] Figure 4 is a plan view showing the first hob included in the tandem hob of Figure 1. [Figure 5] Figure 5 is a plan view showing the second hob included in the tandem hob of Figure 1. [Figure 6] Figure 6 is a plan view showing the collars included in the tandem hob of Figure 1. [Figure 7] Figure 7 is a diagram illustrating how to use the tandem hob shown in Figure 1. [Figure 8] Figure 8 is a cross-sectional view showing one step of the method of using the tandem hob of FIG. 1. [Figure 9] Figure 9 is a cross-sectional view showing another step of the method of using the tandem hob of FIG. 1. [Figure 10] Figure 10 is a cross-sectional view showing another step of the method of using the tandem hob of FIG. 1. [Figure 11] Figure 11 is a cross-sectional view showing another step of the method of using the tandem hob of FIG. 1. [Figure 12] Figure 12 is a cross-sectional view showing another step of the method of using the tandem hob of FIG. 1. [Figure 13] Figure 13 is a cross-sectional view showing another step of the method of using the tandem hob of FIG. 1. [Figure 14] Figure 14 is a cross-sectional view taken along the line I-I of the first hob of FIG. 4. [Figure 15] Figure 15 is a cross-sectional view taken along the line II-II of the second hob of FIG. 5.

Embodiments for Carrying Out the Invention

[0009] One embodiment of the present disclosure relates to the following <1> to <7>.

[0010] <1> A first hob including a plurality of first cutters spaced apart on a first helix centered on a first central axis; A second hob including a plurality of second cutters spaced apart on a second helix centered on a second central axis; A collar connecting the first hob and the second hob such that the first central axis and the second central axis are located on a common axis. In a state where the first hob and the second hob are connected by the collar, The first cutter includes a first cutting edge having a tip on a first side in a circumferential direction centered on the common axis; The second cutter includes a second cutting edge having a tip on a second side opposite to the first side in a circumferential direction centered on the common axis. The first hob and the second hob are tandem hobs whose relative rotation about the common axis and approach along the common axis are restricted.

[0011] <2> The first hob includes the first cutter, a first cylindrical main body portion that supports the first cutter, and a first protruding portion that protrudes from the first cylindrical main body portion toward the second hob along the common axis. The second hob includes the second cutter, a second cylindrical main body portion that supports the second cutter, and a second protruding portion that protrudes from the second cylindrical main body portion toward the first hob along the common axis. The collar has a receiving hole that receives the first protruding portion and the second protruding portion, and the tandem hob according to <1>.

[0012] <3> Due to the contact between the first protruding portion and the collar within the receiving hole, relative rotation of the first hob and the collar about the common axis is restricted. Due to the contact between the second protruding portion and the collar within the receiving hole, relative rotation of the second hob and the collar about the common axis is restricted, and the tandem hob according to <2>.

[0013] <4> Due to the contact between the tip surface of the first protruding portion and the tip surface of the second protruding portion within the receiving hole, approach of the first hob and the second hob along the common axis is restricted, and the tandem hob according to <2> or <3>.

[0014] <5> The tip surface of the first protruding portion is rotationally asymmetric about the common axis. The tip surface of the second protruding portion is rotationally asymmetric about the common axis, and the tandem hob according to <4>.

[0015] <6> The first hob has a first display portion that displays information related to the position of the first helix. The second hob has a second display unit that displays information related to the position of the second helix. <1> ~ <5> A tandem hob as described in any of the following.

[0016] <7> With respect to the tandem hob in which the first hob and the second hob are connected by the aforementioned collar, a reference direction perpendicular to the common axis and a reference axis position on the common axis are defined. The first hob has a first display unit that displays first angular information and first axial position information, The first angular information is information relating to the angle that a line segment connecting a specific position of a particular first cutter and the common axis makes with respect to the reference direction, in an observation along the common axis. The first axial position information is information relating to the distance between the reference axial position and the specific position along the axial direction parallel to the common axis, The second hob has a second display unit that displays second angular information and second axial position information, The second angular information is information relating to the angle that a line segment connecting a specific position of a certain second cutter and the common axis makes with respect to the reference direction, in an observation along the common axis. The second axial position information is information relating to the distance between the reference axial position and the specific position along the axial direction parallel to the common axis. <1> ~ <6> A tandem hob as described in any of the following.

[0017] An embodiment of the present invention will be described below with reference to the drawings. Note that, for the sake of illustration and ease of understanding, the scale and aspect ratios of the drawings attached to this specification have been appropriately altered and exaggerated from those of the actual object. Some components shown in some drawings may be omitted in others. The scale and aspect ratios of the drawings may differ between drawings. Hatching may be omitted in cross-sectional views for the sake of ease of understanding.

[0018] Furthermore, terms used in this specification to specify shapes, geometric conditions, and their degrees, such as "parallel," "orthogonal," and "identical," as well as values ​​for lengths and angles, shall not be strictly interpreted, but shall be interpreted to include a range that allows for the expectation of similar functionality.

[0019] To clarify the directional relationships between drawings, some drawings use arrows with common symbols to indicate the common first axial direction DA1, first circumferential direction DC1, second axial direction DA2, second circumferential direction DC2, axial direction DA, circumferential direction DC, first direction D1, second direction D2, third direction D3, and reference direction DS. The tip of the arrow is the first side of each direction. The opposite side of the arrow is the second side of each direction. Arrows pointing towards the viewer along a direction perpendicular to the plane of the drawing are indicated by a symbol with a dot inside a circle, as shown in Figure 4, for example. Arrows pointing away from the viewer along a direction perpendicular to the plane of the drawing are indicated by a symbol with an "x" inside a circle, as shown in Figure 5, for example.

[0020] As shown in Figure 1, the tandem hob 1 of this embodiment includes a first hob 10, a second hob 20, and a collar 30. The tandem hob 1 cuts a workpiece 100 to form a gear. The tandem hob 1 can be mounted on the shaft member 70 of a hobbing machine 60. The first hob 10 and the second hob 20 can each machine the workpiece 100 independently. The collar 30 connects the first hob 10 and the second hob 20. The first hob 10, the collar 30, and the second hob 20 are located on a common axis CA in this order. When the first hob 10 and the second hob 20 are connected by the collar 30, the first hob 10 and the second hob 20 are restricted from relative rotation about the common axis CA and from approaching each other along the common axis CA.

[0021] With the tandem hob 1 attached to the shaft member 70, the common axis CA coincides with the central axis SA of the shaft member 70. With the tandem hob 1 attached to the shaft member 70, the common axis CA coincides with the rotation axis RA of the shaft member 70.

[0022] The following describes the components of Tandem Hob 1, namely the first hob 10, the second hob 20, and the collar 30, in order.

[0023] As shown in Figure 3, the first hob 10 may be a hole hob. The first hob 10 may be cylindrical in shape as a whole, with the first central axis A1 as its central axis. The first hob 10 may have a first axial hole 19 that opens along the first central axis A1.

[0024] As shown in Figure 2, the first hob 10 includes a first cylindrical body portion 11, a first projection portion 12, and a plurality of first cutters 15. The first cylindrical body portion 11 is cylindrical with a first central axis A1 as its central axis. The first cylindrical body portion 11 supports the plurality of first cutters 15. The first projection portion 12 protrudes from the first cylindrical body portion 11. The first hob 10 has a first shaft hole 19 that penetrates the first cylindrical body portion 11 and the first projection portion 12. The first shaft hole 19 is centered on the first central axis A1.

[0025] The first cylindrical body portion 11, the first projection portion 12, and the plurality of first cutters 15 are integrally formed. The first cylindrical body portion 11, the first projection portion 12, and the plurality of first cutters 15 may also be integrally formed by cutting a metal material.

[0026] As described above, the first cylindrical body portion 11 is cylindrical with the first central axis A1 as its central axis. The first cylindrical body portion 11 has a first inner surface 11a and a first outer surface 11b with the first central axis A1 as its central axis. Here, the diameter of the first inner surface 11a is smaller than the diameter of the first outer surface 11b. The first inner surface 11a defines the first shaft hole 19. Multiple first cutters 15 are located on the first outer surface 11b. The cross-section of the first cylindrical body portion 11 perpendicular to the first axial direction DA1 may have the same shape at any position along the first axial direction DA1.

[0027] A keyway (not shown) may be provided on the first inner surface 11a. The keyway may be used to attach the first hob 10 to the shaft member 70.

[0028] Multiple first cutters 15 are located on the first outer surface 11b. Each first cutter 15 has a first cutting edge 16 that contacts the workpiece 100. The first cutters 15 contact the workpiece 100 and cut the workpiece 100.

[0029] Multiple first cutters 15 are positioned at intervals on a first helix S1 centered on a first central axis A1. Multiple first cutters 15 may be positioned at equal intervals on the first helix S1. As shown in the figure, multiple first cutters 15 may be positioned at equal intervals in the first axial direction DA1. As shown in the figure, multiple first cutters 15 may be positioned at equal intervals in the first circumferential direction DC1. The distance from the first helix S1 to the first central axis A1 may be constant. The first helix S1 may be positioned at a constant pitch in the first axial direction DA1.

[0030] The first axial direction DA1 is parallel to the first central axis A1. The first circumferential direction DC1 is the circumferential direction centered on the first central axis A1.

[0031] The first cutter 15 includes a first cutting edge 16. The first cutting edge 16 cuts into the workpiece 100 and removes material from the workpiece 100. The first cutting edge 16 is located furthest from the first central axis A1 in the first hob 10. The first cutting edge 16 extends along the first helix S1. The first cutting edge 16 has a tip 16a and a trailing end 16b. In the first hob 10, the tip 16a is the end of the first cutting edge 16 located on the first side in the first circumferential direction DC1 (circumferential direction DC). In the first hob, the trailing end 16b is the end of the first cutting edge 16 located on the second side in the first circumferential direction DC1 (circumferential direction DC). The tip 16a and trailing end 16b of the first cutting edges 16 of multiple first cutters 15 are alternately located on the first helix S1. As shown in Figure 4, the distance from the first central axis A1 to the tip 16a is longer than the distance from the first central axis A1 to the rear end 16b. The distance from the first central axis A1 to the first cutting edge 16 decreases as it moves from the tip 16a towards the rear end 16b.

[0032] As shown in Figure 2, the first projection 12 protrudes from the first cylindrical body portion 11 along the first central axis A1. The first projection 12 protrudes from the first cylindrical body portion 11 on the first side in the first axial direction DA1. The first projection 12 protrudes from the end face of the first cylindrical body portion 11 located on the first side in the first axial direction DA1.

[0033] The first projection 12 has a first tip surface 13. The first tip surface 13 is perpendicular to the first central axis A1. The first tip surface 13 is perpendicular to the first axial direction DA1. The first tip surface 13 may be rotationally asymmetric about the first central axis A1. For example, the first tip surface 13 may have an outer contour formed by cutting out a part of an annule. Specifically, as shown in Figure 4, the first tip surface 13 may be formed by two identical arcs 13a centered on the first central axis A1, and two straight lines (chords) 13b and 13c of different lengths, respectively, located between the ends of the two arcs.

[0034] The first projection 12 may include a first base projection 12a and a first tip projection 12b. In the first axial direction DA1, the first base projection 12a is located between the first cylindrical body portion 11 and the first tip projection 12b. The first base projection 12a is connected to the first cylindrical body portion 11. The first base projection 12a may be cylindrical with the first central axis A1 as its central axis. The cross-section of the first base projection 12a perpendicular to the first axial direction DA1 may have the same shape at any position along the first axial direction DA1.

[0035] The first tip projection 12b protrudes from the first base projection 12a along the first central axis A1. The first tip projection 12b is a cylindrical portion located on a portion of the end face of the first base projection 12a. The first tip projection 12b forms the first tip surface 13 of the first projection 12. The cross-section of the first tip projection 12b perpendicular to the first central axis A1 has the same shape as the first tip surface 13 of the first projection 12. The cross-section of the first tip projection 12b perpendicular to the first axial direction DA1 may have the same shape at any position along the first axial direction DA1.

[0036] If the first tip surface 13 is formed by two circular arcs 13a and two straight lines 13b, 13c, the radius of the circular arc 13a may be the same as the radius of the first base projection 12a. The first tip projection 12b has a first side surface 14 connected to the first tip surface 13. The first side surface 14 of the first tip projection 12b has a pair of first curved surfaces 14a and a first long plane 14b and a first short plane 14c connecting the pair of first curved surfaces 14a. The pair of first curved surfaces 14a have a symmetrical shape. The first long plane 14b and the first short plane 14c have the same length along the first axial direction DA1. The first long plane 14b and the first short plane 14c have different lengths along the direction perpendicular to the first axial direction DA1. The length LB1 of the first long plane 14b along the direction perpendicular to the first axis direction DA1 is longer than the length LC1 of the first short plane 14c along the direction perpendicular to the first axis direction DA1. The distance from the first central axis A1 to the first long plane 14b is different from the distance from the first central axis A1 to the first short plane 14c. The distance HB1 from the first central axis A1 to the first long plane 14b is shorter than the distance HC1 from the first central axis A1 to the first short plane 14c.

[0037] Next, the second hob 20 will be described. As shown in Figure 3, the second hob 20 may be a hole hob. The second hob 20 may be cylindrical in shape as a whole, with the second central axis A2 as its central axis. The second hob 20 may have a second axial hole 29 that opens along the second central axis A2.

[0038] As shown in Figure 2, the second hob 20 includes a second cylindrical body portion 21, a second projection portion 22, and a plurality of second cutters 25. The second cylindrical body portion 21 is cylindrical with a second central axis A2 as its central axis. The second cylindrical body portion 21 supports the plurality of second cutters 25. The second projection portion 22 protrudes from the second cylindrical body portion 21. The second hob 20 has a second shaft hole 29 that penetrates the second cylindrical body portion 21 and the second projection portion 22. The second shaft hole 29 is centered on the second central axis A2.

[0039] The second cylindrical body portion 21, the second projection portion 22, and the plurality of second cutters 25 are integrally formed. The second cylindrical body portion 21, the second projection portion 22, and the plurality of second cutters 25 may also be integrally formed by cutting a metal material.

[0040] As described above, the second cylindrical body portion 21 is cylindrical with the second central axis A2 as its central axis. The second cylindrical body portion 21 has a second inner surface 21a and a second outer surface 21b with the second central axis A2 as its central axis. Here, the diameter of the second inner surface 21a is smaller than the diameter of the second outer surface 21b. The second inner surface 21a defines the second shaft hole 29. Multiple second cutters 25 are located on the second outer surface 21b. The cross-section of the second cylindrical body portion 21 perpendicular to the second axial direction DA2 may have the same shape at any position along the second axial direction DA2.

[0041] A keyway (not shown) may be provided on the second inner surface 21a. The keyway may be used to attach the second hob 20 to the shaft member 70.

[0042] Multiple second cutters 25 are located on the second outer surface 21b. Each second cutter 25 has a second cutting edge 26 that contacts the workpiece 100. The second cutters 25 contact the workpiece 100 and cut the workpiece 100.

[0043] Multiple second cutters 25 are positioned at intervals on a second helix S2 centered on a second central axis A2. Multiple second cutters 25 may be positioned at equal intervals on the second helix S2. As shown in the figure, multiple second cutters 25 may be positioned at equal intervals in the second axial direction DA2. As shown in the figure, multiple second cutters 25 may be positioned at equal intervals in the second circumferential direction DC2. The distance from the second helix S2 to the second central axis A2 may be constant. The second helix S2 may be positioned at a constant pitch in the second axial direction DA2.

[0044] The second helix S2 may be oriented in the same direction as the first helix S1 when connected using the collar 30. For example, the second helix S2 and the first helix S1 may form a right-hand thread. The second helix S2 and the first helix S1 may also form a left-hand thread. The second helix S2 and the first helix S1 may have the same pitch.

[0045] The second axial direction DA2 is parallel to the second central axis A2. The second circumferential direction DC2 is the circumferential direction centered on the second central axis A2.

[0046] The second cutter 25 includes a second cutting edge 26. The second cutting edge 26 cuts into the workpiece 100 and removes material from the workpiece 100. The second cutting edge 26 is located furthest from the second central axis A2 in the second hob 20. The second cutting edge 26 extends along the second helix S2. The second cutting edge 26 has a tip 26a and a trailing end 26b. In the second hob 20, the tip 26a is the end of the second cutting edge 26 located on the second side in the second circumferential direction DC2 (circumferential direction DC). In the second hob 20, the trailing end 26b is the end of the second cutting edge 26 located on the first side in the second circumferential direction DC2 (circumferential direction DC). The tip 26a and trailing end 26b of the second cutting edges 26 of multiple second cutters 25 are alternately located on the second helix S2. As shown in Figure 5, the distance from the second central axis A2 to the tip 26a is longer than the distance from the second central axis A2 to the rear end 26b. The distance from the first central axis A1 to the second cutting edge 26 decreases as it moves from the tip 26a towards the rear end 26b.

[0047] As shown in Figure 2, the second projection 22 protrudes from the second cylindrical body portion 21 along the second central axis A2. The second projection 22 protrudes from the second cylindrical body portion 21 on the second side in the second axial direction DA2. The second projection 22 protrudes from the end face of the second cylindrical body portion 21 located on the second side in the second axial direction DA2.

[0048] The second projection 22 has a second tip surface 23. The second tip surface 23 is perpendicular to the second central axis A2. The second tip surface 23 is perpendicular to the second axial direction DA2. The second tip surface 23 may be rotationally asymmetric about the second central axis A2. For example, the second tip surface 23 may have an outer contour formed by cutting off a part of an annule. Specifically, as shown in Figure 5, the second tip surface 23 may be formed by two identical arcs 23a centered on the second central axis A2, and two straight lines (chords) 23b and 23c of different lengths, located between the ends of the two arcs, respectively.

[0049] The second projection 22 may include a second base projection 22a and a second tip projection 22b. In the second axial direction DA2, the second base projection 22a is located between the second cylindrical body portion 21 and the second tip projection 22b. The second base projection 22a is connected to the second cylindrical body portion 21. The second base projection 22a may be cylindrical with the second central axis A2 as its central axis. The cross-section of the second base projection 22a perpendicular to the second axial direction DA2 may have the same shape at any position along the second axial direction DA2.

[0050] The second tip projection 22b protrudes from the second base projection 22a along the second central axis A2. The second tip projection 22b is a cylindrical portion located on a portion of the end face of the second base projection 22a. The second tip projection 22b forms the second tip surface 23 of the second projection 22. The cross-section of the second tip projection 22b perpendicular to the second central axis A2 is the same shape as the second tip surface 23 of the second projection 22. The cross-section of the second tip projection 22b perpendicular to the second axial direction DA2 may have the same shape at any position along the second axial direction DA2.

[0051] When the second tip surface 23 is formed by two circular arcs 23a and two straight lines 23b, 23c, the radius of the circular arc 23a may be the same as the radius of the second base projection 22a. The second tip projection 22b has a second side surface 24 connected to the second tip surface 23. The second side surface 24 of the second tip projection 22b has a pair of second curved surfaces 24a and a second long plane 24b and a second short plane 24c connecting the pair of second curved surfaces 24a. The pair of second curved surfaces 24a have a symmetrical shape. The second long plane 24b and the second short plane 24c have the same length along the second axial direction DA2. The second long plane 24b and the second short plane 24c have different lengths along the direction perpendicular to the second axial direction DA2. The length LB2 of the second long plane 24b along the direction perpendicular to the second axis direction DA2 is longer than the length LC2 of the second short plane 24c along the direction perpendicular to the second axis direction DA2. The distance from the second central axis A2 to the second long plane 24b is different from the distance from the second central axis A2 to the second short plane 24c. The distance HB2 from the second central axis A2 to the second long plane 24b is shorter than the distance HC2 from the second central axis A2 to the second short plane 24c.

[0052] Next, the collar 30 will be described. The collar 30 connects the first hob 10 and the second hob 20 such that the first central axis A1 and the second central axis A2 are located on the common axis CA. The collar 30 connects the first hob 10 and the second hob 20 such that the first axial direction DA1 and the second axial direction DA2 are parallel to the axial direction DA. The axial direction DA is parallel to the common axis CA. The collar 30 connects the first hob 10 and the second hob 20 so as to restrict their relative rotation around the common axis CA. The collar 30 connects the first hob 10 and the second hob 20 so as to restrict their approach to each other along the common axis CA.

[0053] As shown in Figure 3, the collar 30 has receiving holes 35 for the first projection 12 and the second projection 22. In the illustrated example, the first projection 12 and the second projection 22 are inserted into a single common receiving hole 35 from different sides in the axial direction DA. Specifically, the first projection 12 is inserted into the receiving hole 35 from the second side in the axial direction DA, and the second projection 22 is inserted into the receiving hole 35 from the first side in the axial direction DA.

[0054] In the illustrated example, the contact between the first projection 12 and the collar 30 within the receiving hole 35 restricts the relative rotation of the first hob 10 and the collar 30 about the common axis CA. The contact between the second projection 22 and the collar 30 within the receiving hole 35 restricts the relative rotation of the second hob 20 and the collar 30 about the common axis CA. In this example, the relative rotation of the first hob 10 and the second hob 20 about the common axis CA is restricted via the collar 30. In the illustrated example, the contact between the first tip surface 13 of the first projection 12 and the second tip surface 23 of the second projection 22 within the receiving hole 35 restricts the approach of the first hob 10 and the second hob 20 along the common axis CA.

[0055] As shown in the figure, the collar 30 may be annular. The receiving hole 35 may be surrounded all around by the collar 30. The shape of the receiving hole 35 observed from the axial direction DA may be rotationally asymmetric about the common axis CA.

[0056] The collar 30 has an inner wall surface 31 that defines the receiving hole 35. The contact between the inner wall surface 31 of the collar 30 and the first side surface 14 of the first tip projection 12b inserted into the receiving hole 35 restricts the relative rotation of the first hob 10 and the collar 30 about the common axis CA. The contact between the inner wall surface 31 of the collar 30 and the second side surface 24 of the second tip projection 22b inserted into the receiving hole 35 restricts the relative rotation of the second hob 20 and the collar 30 about the common axis CA.

[0057] As shown in Figure 6, the inner wall surface 31 of the collar 30 has a pair of curved surfaces 31a and a first restricting surface 31b and a second restricting surface 31c that connect the pair of curved surfaces 31a. The pair of curved surfaces 31a have a symmetrical shape. The first restricting surface 31b and the second restricting surface 31c have the same length along the axial direction DA. The first restricting surface 31b and the second restricting surface 31c have different lengths along the direction perpendicular to the axial direction DA. The length LB3 of the first restricting surface 31b along the direction perpendicular to the axial direction DA is longer than the length LC3 of the second restricting surface 31c along the direction perpendicular to the axial direction DA. The distance from the common axis CA to the first restricting surface 31b is different from the distance from the common axis CA to the second restricting surface 31c. The distance HB3 from the common axis CA to the first restricting surface 31b is shorter than the distance HC3 from the common axis CA to the second restricting surface 31c.

[0058] A pair of curved surfaces 31a of the inner wall surface 31 may face and contact a pair of first curved surfaces 14a of the first side surface 14 inserted into the receiving hole 35. A first restricting surface 31b may face and contact a first long plane 14b of the first side surface 14 inserted into the receiving hole 35. A second restricting surface 31c may face and contact a first short plane 14c of the first side surface 14 inserted into the receiving hole 35. A pair of curved surfaces 31a of the inner wall surface 31 may face and contact a pair of second curved surfaces 24a of the second side surface 24 inserted into the receiving hole 35. A first restricting surface 31b may face and contact a second long plane 24b of the second side surface 24 inserted into the receiving hole 35. A second restricting surface 31c may face and contact a second short plane 24c of the second side surface 24 inserted into the receiving hole 35.

[0059] In the illustrated example, with the first hob 10 and the second hob 20 connected by the collar 30, the first restricting surface 31b is parallel to the first long plane 14b. Also, the first restricting surface 31b is parallel to the second long plane 24b. Therefore, the first long plane 14b and the second long plane 24b are parallel. In the illustrated example, with the first hob 10 and the second hob 20 connected by the collar 30, the second restricting surface 31c is parallel to the first short plane 14c. Also, the second restricting surface 31c is parallel to the second short plane 24c. Therefore, the first short plane 14c and the second short plane 24c are parallel.

[0060] In the illustrated example, with the first hob 10 and the second hob 20 connected by the collar 30, one of the pair of curved surfaces 31a is parallel to one of the pair of first curved surfaces 14a. Also, one of the pair of curved surfaces 31a is parallel to one of the pair of second curved surfaces 24a. Therefore, one of the pair of first curved surfaces 14a and one of the pair of second curved surfaces 24a are parallel. In the illustrated example, with the first hob 10 and the second hob 20 connected by the collar 30, the other of the pair of curved surfaces 31a is parallel to the other of the pair of first curved surfaces 14a. Also, the other of the pair of curved surfaces 31a is parallel to the other of the pair of second curved surfaces 24a. Therefore, the other of the pair of first curved surfaces 14a and the other of the pair of second curved surfaces 24a are parallel.

[0061] As shown in Figure 2, the length W3 of the collar 30 along the axial direction DA is longer than the length W1 of the first tip projection 12b along the first axial direction DA1. The length W3 of the collar 30 along the axial direction DA is longer than the length W2 of the second tip projection 22b along the second axial direction DA2. As shown in Figure 2, the length W3 of the collar 30 along the axial direction DA is shorter than the sum of the length W1 of the first tip projection 12b along the first axial direction DA1 and the length W2 of the second tip projection 22b along the second axial direction DA2.

[0062] In the illustrated example, with the collar 30 connecting the first hob and the second hob 20, the first axial direction DA1 is parallel to the second axial direction DA2. With the collar 30 connecting the first hob 10 and the second hob 20, the first side in the first axial direction DA1 and the first side in the second axial direction DA2 become the first side in the axial direction DA. With the collar 30 connecting the first hob 10 and the second hob 20, the second side in the first axial direction DA1 and the second side in the second axial direction DA2 become the second side in the axial direction DA.

[0063] In the illustrated example, with the collar 30 connecting the first hob 10 and the second hob 20, the first circumferential direction DC1 is parallel to the second circumferential direction DC2. With the collar 30 connecting the first hob 10 and the second hob 20, the first side in the first circumferential direction DC1 and the first side in the second circumferential direction DC2 become the first side in the circumferential direction DC. With the collar 30 connecting the first hob 10 and the second hob 20, the second side in the first circumferential direction DC1 and the second side in the second circumferential direction DC2 become the second side in the circumferential direction DC. With the collar 30 connecting the first hob 10 and the second hob 20, the first helix S1 and the second helix S2 are oriented in the same direction. Note that the circumferential direction DC is the circumferential direction centered on the common axis CA.

[0064] Next, we will explain how to use the Tandem Hob 1.

[0065] The tandem hob 1 is used attached to the shaft member 70 of the hobbing machine 60. The shaft member 70 is cylindrical with a central axis SA. As shown in Figure 7, the tandem hob 1 is attached to the shaft member 70 by inserting the shaft member 70 into the first shaft hole 19 and the second shaft hole 29, and then securing it with fasteners such as nuts. When the tandem hob 1 is attached to the shaft member 70, the common axis CA coincides with the central axis SA of the shaft member 70. When the tandem hob 1 is attached to the shaft member 70, its detachment from the shaft member 70 is restricted. Examples of means for restricting the relative movement of the tandem hob 1 with respect to the shaft member 70 include flanges, nuts, and keyways.

[0066] The shaft member 70 is movable in a first direction D1 parallel to the central axis SA, a second direction D2 perpendicular to the first direction D1, and a third direction D3 perpendicular to both the first and second directions D1 and D2. The shaft member 70 is also rotatable about the central axis SA. That is, the central axis SA of the shaft member 70 coincides with the rotation axis RA of the shaft member 70. Rotation of the shaft member 70 about the central axis SA can be performed in both directions. As the shaft member 70 rotates about the central axis SA, the tandem hob 1 rotates about the common axis CA.

[0067] In the illustrated example, with the tandem hob 1 attached to the shaft member 70, the axial direction DA is parallel to the first direction D1. In the illustrated example, with the tandem hob 1 attached to the shaft member 70, the first side in the axial direction DA is the first side in the first direction D1. In the illustrated example, with the tandem hob 1 attached to the shaft member 70, the second side in the axial direction DA is the second side in the first direction D1.

[0068] The workpiece 100 to be processed is disc-shaped or cylindrical with respect to its central axis A100. Metal is an example of the material of the workpiece 100. As shown in Figure 7, the workpiece 100 is mounted on the hobbing machine 60 such that its central axis A100 is parallel to the third direction D3. The workpiece 100 is rotated by the hobbing machine 60 around its central axis A100.

[0069] After mounting the tandem hob 1 and workpiece 100 to the hobbing machine 60, the workpiece 100 is machined using the tandem hob 1. In the illustrated example, the workpiece 100 is machined using the first hob 10, and then the workpiece 100 is machined using the second hob 20. The example is not limited to the illustrated example; the workpiece 100 may be machined using the second hob 20, and then the workpiece 100 may be machined using the first hob 10.

[0070] Referring to Figures 8 to 12, an example of a method for machining workpiece 100 using tandem hob 1 will be explained.

[0071] First, as shown in Figure 8, the shaft member 70 and the workpiece 100 are rotated respectively, and the shaft member 70 is moved toward the first side in the second direction D2 to bring the first hob 10 into contact with the workpiece 100. At this time, the rotation of the shaft member 70 is toward the first side in the circumferential direction DC, which is counterclockwise in the plane of Figure 8. When the first hob 10 comes into contact with the workpiece 100, the first cutter 15 cuts the side surface of the workpiece 100, as shown in Figure 9. At this time, the tip 16a of the first cutting edge 16 is the first to contact the workpiece 100. As the shaft member 70 rotates, multiple first cutters 15 move toward the circumferential direction DC, cutting the workpiece 100 one after another. As the first cutters 15 move, the workpiece 100 is rotated, and a groove along the third direction D3 is formed along the entire circumference of the side surface of the workpiece 100 by cutting.

[0072] As shown in Figure 9, the first hob 10 may form a groove by cutting only the second end of the workpiece 100 in the illustrated third direction D3. Not limited to the illustrated example, the first hob 10 may also form a groove extending from one end to the other in the third direction D3 of the workpiece 100 by rotating about the central axis SA of the shaft member 70 and moving in the third direction D3. The direction in which the shaft member 70 moves in the third direction D3 is not particularly limited. The shaft member 70 may move from the first side to the second side in the third direction D3, or from the second side to the first side in the third direction D3. If the first hob 10 forms a groove extending from one end to the other in the third direction D3 of the workpiece 100, a burr will be generated on the first side of the workpiece 100 in the illustrated third direction D3.

[0073] After machining the workpiece 100 with the first hob 10, as shown in Figure 10, the shaft member 70 is moved toward the second side in the second direction D2, and the first hob 10 is moved away from the workpiece 100. Once the first hob 10 is sufficiently far from the workpiece 100, the shaft member 70 is moved toward the second side in the first direction D1 by a shift distance LS, and the second hob 20 is brought into contact with the workpiece 100 in the second direction D2. The method for determining the shift distance LS will be described later. Then, the shaft member 70 is rotated in the reverse direction. That is, the shaft member 70 is rotated toward the second side in the circumferential direction DC. As shown in Figure 11, with the shaft member 70 rotated, the shaft member 70 is moved toward the first side in the second direction D2, and the second hob 20 is brought into contact with the workpiece 100.

[0074] When the second hob 20 contacts the workpiece 100, the second cutter 25 further cuts the groove formed in the workpiece 100 by the first hob 10. At this time, the tip 26a of the second cutting edge 26 first contacts the workpiece 100. As the shaft member 70 rotates, the multiple second cutters 25 move in the circumferential direction DC, cutting the workpiece 100 one after the other. As the second cutters 25 move, the workpiece 100 is rotated, and a groove along the third direction D3 is formed by cutting around the entire circumference of the side surface of the workpiece 100. As shown in Figure 12, by rotating the shaft member 70 and moving it in the third direction D3, the second cutters 25 cut the workpiece 100 so that a groove extending from one end to the other in the third direction of the workpiece 100 is formed. The direction in which the shaft member 70 moves in the third direction D3 is not particularly limited. The example is not limited to the one shown in the illustration. As described above, if the first hob 10 forms a groove extending from one end to the other in the third direction D3 of the workpiece 100, only the first end in the third direction D3 shown in the illustration may be cut. In other words, burrs generated by machining with the first hob 10 may be cut.

[0075] As described above, by cutting the workpiece 100 from both directions using the first hob 10 and the second hob 20, burrs are not generated on the finished gear, and high-precision gears can be manufactured.

[0076] Incidentally, the position of the groove formed in the workpiece 100 by the first cutter 15 and the position of the groove formed in the workpiece by the second cutter 25 must coincide in the axial direction DA. That is, as shown in Figure 13, the second cutter 25 of the second hob 20 must face the groove formed in the workpiece 100 by the first hob 10. For this reason, the shift distance LS must satisfy the following equation (1). Note that it is assumed that the first helix S1 and the second helix S2 are the same. LS = LO + n × T Equation (1)

[0077] In equation (1), LO is the offset distance. n is any integer. T is the pitch of the first helix S1 and the second helix S2. The offset distance LO represents the phase difference of the first helix S1 and the second helix S2 along the axial direction DA. In other words, the phase difference is the amount of axial displacement DA of the first helix S1 and the second helix S2. Therefore, if the first helix S1 is moved axially by the offset distance LO, the first helix S1 will overlap with the second helix S2. Thus, in order to properly machine the workpiece 100, it is necessary to know the offset distance LO.

[0078] To determine the offset distance LO, information 40 regarding the position of the first helix S1 and information 50 regarding the position of the second helix S2 are required when the first hob 10 and the second hob 20 are connected by the collar 30. For example, the information 40 regarding the position of the first helix S1 may be the first angle information 41 and the first axial position information 42 of the first hob 10. The information 50 regarding the position of the second helix S2 may be the second angle information 51 and the second axial position information 52 of the second hob 20.

[0079] As shown in Figure 4, the first angle information 41 is information regarding the angle θ1 made with respect to the reference direction DS by a line segment connecting a specific position X1 of a certain first cutter 15 and the common axis CA, when observed along the common axis CA. Here, the reference direction DS is the direction perpendicular to the common axis CA. As shown in the example in Figure 4, the reference direction DS may be a plane parallel to the first short plane 14c. That is, the reference direction DS may be a direction parallel to the first short plane 14c and perpendicular to the common axis CA. Therefore, the first angle information 41 can be set by the first hob 10 alone. The specific position X1 may be the center of the tip 16a of the first cutting edge 16 of a certain first cutter 15 in the first axial direction DA1, as shown in Figure 14.

[0080] As shown in Figure 14, the first axial position information 42 is information regarding the distance H1 between a reference axial position O along the axial direction DA and a specific position X1. Here, the reference axial position O is a certain position on the common axis CA. As shown in Figure 14, the reference axial position O may also be the position where the first tip surface 13 (a virtual surface defined by the first tip surface 13) intersects with the first central axis A1. Therefore, the first axial position information 42 can be set by the first hob 10 alone.

[0081] As shown in Figure 5, the second angle information 51 is information regarding the angle θ2 made with respect to the reference direction DS by a line segment connecting a specific position X2 of a certain second cutter 25 and the common axis CA, when observed along the common axis CA. As described above, the reference direction DS may be a direction parallel to the first short plane 14c and perpendicular to the common axis CA. In the illustrated example, with the first hob 10 and the second hob 20 connected by the collar 30, the first short plane 14c is parallel to the second restricting surface 31c that defines the receiving hole 35 of the collar 30. Also, the second short plane 24c of the second hob 20 is parallel to the second restricting surface 31c. Therefore, the reference direction DS is a direction parallel to the second short plane 24c and perpendicular to the common axis CA. Thus, in this example, the second angle information 51 can be set for the second hob 20 alone. The specific position X2 may be the center in the second axial direction DA2 of the tip 26a of the second cutting edge 26 of a certain second cutter 25, as shown in Figure 15.

[0082] As shown in Figure 15, the second axial position information 52 is information regarding the distance H2 between a reference axial position O along the axial direction DA and a specific position X2. As described above, the reference axial position O may be the position where the first end face 13 (a virtual surface defined by the first end face 13) intersects with the first central axis A1. In the illustrated example, with the first hob 10 and the second hob 20 connected by the collar 30, the first end face 13 is in surface contact with the second end face 23. Therefore, the position where the first end face 13 (a virtual surface defined by the first end face 13) intersects with the first central axis A1 coincides with the position where the second end face 23 (a virtual surface defined by the second end face 23) intersects with the second central axis A2. Thus, the second axial position information 52 can be set for the second hob 20 alone.

[0083] From the first angle information 41, the first axial position information 42, the second angle information 51, and the second axial position information 52, the offset distance LO can be determined by the following equation (2). LO=H1+H2-(θ1-θ2) / 360×T Formula (2)

[0084] The information 40 related to the position of the first helix S1 and the information 50 related to the position of the second helix S2 can be obtained in advance. Therefore, the first hob 10 may have a first display unit 17 that displays the information 40 related to the position of the first helix S1, i.e., the first angle information 41 and the first axial position information 42. The second hob 20 may have a second display unit 27 that displays the information related to the position of the second helix S2, i.e., the second angle information 51 and the second axial position information 52. The first angle information 41 and the first axial position information 42 may be engraved on the first display unit 17, for example. The second angle information 51 and the second axial position information 52 may be engraved on the second display unit 27, for example.

[0085] The tandem hob 1 according to the embodiment described above comprises a first hob 10 including a plurality of first cutters 15 positioned at intervals on a first helix S1 centered on a first central axis A1, a second hob 20 including a plurality of second cutters 25 positioned at intervals on a second helix S2 centered on a second central axis A2, and a collar 30 connecting the first hob 10 and the second hob 20 such that the first central axis A1 and the second central axis A2 are located on a common axis CA. When the first hob 10 and the second hob 20 are connected by the collar 30, the first cutter 15 includes a cutting edge 16 having a tip 16a on the first side in the circumferential direction DC centered on the common axis CA. The second cutter 25 includes a cutting edge 26 having a tip 26a on the second side opposite to the first side in the circumferential direction DC centered on the common axis CA. The first hob 10 and the second hob 20 are restricted from relative rotation about the common axis CA and from approaching each other along the common axis CA.

[0086] The tandem hob 1 can be attached to the shaft member 70 of the hobbing machine 60 with the first hob 10 and the second hob 20 connected by a collar 30. In the connected state, the relative rotation of the first hob and the second hob 20 around the common axis CA and their approach along the common axis CA are restricted, so it is not necessary to determine the relative positions of the first hob 10 and the second hob 20 on the shaft member 70. Therefore, the tandem hob 1 can be easily attached to the shaft member 70.

[0087] The first hob 10, collar 30, and second hob 20 constituting the tandem hob 1 may be attached to the shaft member 70 in order. The first hob 10 and collar 30 are connected to each other in a predetermined relative position. The second hob 20 and collar 30 are connected to each other in a predetermined relative position. Therefore, the first hob 10, collar 30, and second hob 20 can be easily positioned in predetermined relative positions on the shaft member 70. As a result, the tandem hob 1 can be easily attached to the shaft member 70.

[0088] Furthermore, the fact that the first hob 10 and the second hob 20 are separate components offers several advantages. For example, the tandem hob 1 according to this embodiment is easy to polish. Generally, hob polishing is performed row by row by row by row by row of cutters that are spaced apart in the axial direction. If the two hobs were a single unit, there is a risk that the grinding wheel will come into contact with and damage the cutters of the other hob when polishing the row of cutters on one hob. Therefore, it is difficult to polish all the way to the end. On the other hand, according to this embodiment, the first hob 10 and the second hob 20 can each be polished individually in the usual manner, making polishing easy.

[0089] Furthermore, the first hob 10 and the second hob 20 can be replaced with new ones at different times, and their combinations can also be changed. In addition, the first hob and the second hob 20 can be used individually without being connected.

[0090] In the specific example of the embodiment described above, the first hob 10 includes a first cutter 15, a first cylindrical body portion 11 that supports the first cutter 15, and a first projection 12 that protrudes from the first cylindrical body portion 11 toward the second hob along a common axis CA. The second hob 20 includes a second cutter 25, a second cylindrical body portion 21 that supports the second cutter 25, and a second projection 22 that protrudes from the second cylindrical body portion 21 toward the first hob 10 along a common axis CA. The collar 30 has receiving holes 35 that receive the first projection 12 and the second projection 22.

[0091] The first hob 10 and the second hob 20 can be connected by the collar 30 by fitting the first protrusion 12 and the second protrusion 22 into the receiving hole 35. Therefore, the tandem hob 1 can be easily connected and positioned and assembled on the shaft member 70. Thus, the tandem hob 1 can be easily attached on the shaft member 70.

[0092] In the specific example of the embodiment described above, the contact between the first protrusion 12 and the collar 30 within the receiving hole 35 restricts the relative rotation of the first hob 10 and the collar 30 around the common axis CA. The contact between the second protrusion 22 and the collar 30 within the receiving hole 35 restricts the relative rotation of the second hob 20 and the collar 30 around the common axis CA. Therefore, the relative rotation of the first hob 10 and the second hob 20 around the common axis CA can be stably restricted.

[0093] In the specific example of the embodiment described above, the tip surface 13 of the first projection 12 is rotationally asymmetric about the common axis CA. The tip surface 23 of the second projection 22 is rotationally asymmetric about the common axis CA.

[0094] According to this embodiment, the relative rotational positions of the first hob 10 and the second hob 20 when connected are uniquely determined around the common axis CA. That is, the first hob 10 and the second hob 20 can be easily connected to the appropriate position. Therefore, the tandem hob 1 can be easily attached to the shaft member 70.

[0095] In the specific example of the embodiment described above, the first hob 10 has a first display unit 17 that displays information 40 related to the position of the first helix S1. The second hob 20 has a second display unit 27 that displays information 50 related to the position of the second helix S2.

[0096] From the information 40 related to the position of the first helix S1 and the information 50 related to the position of the second helix S2, the axial displacement of the first helix S1 and the second helix S2 can be calculated. Therefore, the shift distance LS of the shaft member 70 required to align the cutting edges 16,26 of the other hob 10 and the second hob 20 with the groove of the workpiece 100 formed by one of the first hob 10 and the second hob 20 can be calculated. Thus, the other hob 10 and the second hob 20 can be easily and accurately positioned relative to the workpiece 100 that has been machined by one of the first hob 10 and the second hob 20.

[0097] In the specific example of the embodiment described above, a reference direction DS perpendicular to the common axis CA and a reference axis position O on the common axis CA are defined for a tandem hob in which the first hob 10 and the second hob 20 are connected by a collar 30. The first hob 10 has a first display unit 17 that displays first angle information 41 and first axis position information 42. The first angle information 41 is information regarding the angle θ1 made with respect to the reference direction DS by a line segment connecting a specific position X1 of a certain first cutter 15 and the common axis CA in an observation along the common axis CA. The first axis position information 42 is information regarding the distance H1 between the reference axis position O and the specific position X1 along the axis DA parallel to the common axis CA. The second hob 20 has a second display unit 27 that displays second angle information 51 and second axial position information 52. The second angle information 51 is information regarding the angle θ2 with respect to the reference direction made by a line segment connecting a specific position X2 of a certain second cutter 25 and the common axis CA, in an observation along the common axis CA. The second axial position information 52 is information regarding the distance H2 between the reference axial position O along the axial direction parallel to the common axis CA and the specific position X2.

[0098] Based on the first angle information 41, the first axial position information 42, the second angle information 51, and the second axial position information 52, the shift distance LS of the shaft member 70 required to align the cutting edges 16,26 of the other hob 10 and 2 hob 20 with the groove formed in the workpiece 100 by one of the first hob 10 and 2 hob 20 can be calculated. Therefore, the other hob 10 and 2 hob can be easily and accurately positioned relative to the workpiece 100 that has been machined by one of the first hob 10 and 2 hob 20.

[0099] The embodiments of this disclosure are not limited to those described above, but include various modifications that a person skilled in the art could conceive, and the effects of this disclosure are not limited to those of the embodiments described above. Various additions, modifications, and partial deletions are possible, provided that they do not depart from the conceptual idea and spirit of each disclosure derived from the claims and their equivalents. [Explanation of Symbols]

[0100] 1: Tandem hob, 10: First hob, 11: First cylindrical body, 12: First projection, 13: First tip surface, 15: First cutter, 16: First cutting edge, 16a: Tip, 16b: Rear end, 17: First indicator, 19: First shaft hole, 20: Second hob, 21: Second cylindrical body, 22: Second projection, 23: Second tip surface, 25: Second cutter, 26: Second cutting edge, 26a: Tip, 26b: Rear end, 27: Second indicator, 29: Second shaft hole, 30: Collar, 35: Receiving hole, 40: Information related to the first helix S1, 41: First angle information, 42: First axial position information, 50: Information related to the second helix S2, 51: Second angle information, 52: Second axial position information, 60: Hobbing machine, 70: Shaft member, 100: Workpiece, CA: Common axis, A1: First central axis, A2: Second central axis, S1: First helix, S2: Second helix, DS: Reference direction, O: Reference axial position, θ1: Angle, θ2: Angle, H1: Distance, H2: Distance

Claims

1. A first hob including a plurality of first cutters positioned at intervals on a first spiral centered on a first central axis, A second hob including multiple second cutters positioned at intervals on a second spiral centered on a second central axis, A collar connecting the first hob and the second hob, such that the first central axis and the second central axis are located on a common axis, In the state in which the first hob and the second hob are connected by the collar, The first cutter includes a first cutting edge having its tip on the first side in the circumferential direction centered on the common axis, The second cutter includes a second cutting edge having its tip on the second side opposite to the first side in the circumferential direction with respect to the common axis, The first hob and the second hob are tandem hobs whose relative rotation about the common axis and approach along the common axis are restricted.

2. The first hob includes the first cutter, a first cylindrical body portion supporting the first cutter, and a first projection portion projecting from the first cylindrical body portion toward the second hob along the common axis. The second hob includes the second cutter, a second cylindrical body supporting the second cutter, and a second projection extending from the second cylindrical body toward the first hob along the common axis. The tandem hob according to claim 1, wherein the collar has receiving holes for the first projection and the second projection.

3. The contact between the first protrusion and the collar within the receiving hole restricts the relative rotation of the first hob and the collar about the common axis. The tandem hob according to claim 2, wherein the contact between the second projection and the collar within the receiving hole restricts the relative rotation of the second hob and the collar about the common axis.

4. The tandem hob according to claim 2, wherein the contact between the tip surface of the first projection and the tip surface of the second projection within the receiving hole restricts the approach of the first hob and the second hob along the common axis.

5. The tip surface of the first projection is rotationally asymmetrical with respect to the common axis. The tandem hob according to claim 4, wherein the tip surface of the second projection is rotationally asymmetrical with respect to the common axis.

6. The first hob has a first display unit that displays information related to the position of the first helix, The tandem hob according to claim 1, wherein the second hob has a second display unit that displays information relating to the position of the second helix.

7. With respect to the tandem hob in which the first hob and the second hob are connected by the aforementioned collar, a reference direction perpendicular to the common axis and a reference axis position on the common axis are defined. The first hob has a first display unit that displays first angular information and first axial position information, The first angle information is information relating to the angle that a line segment connecting a specific position of a particular first cutter and the common axis makes with respect to the reference direction, in an observation along the common axis. The first axial position information is information relating to the distance between the reference axial position and the specific position along the axial direction parallel to the common axis, The second hob has a second display unit that displays second angular information and second axial position information, The second angular information is information relating to the angle that a line segment connecting a specific position of a second cutter and the common axis makes with respect to the reference direction, in an observation along the common axis. The tandem hob according to claim 1, wherein the second axial position information is information relating to the distance between the reference axial position and the specific position along the axial direction parallel to the common axis.

Images