A kind of expansion sleeve type gear hobbing fixture

Abstract

The application discloses a kind of expansion sleeve type gear hobbing fixture, it is related to tooling fixture technical field, at least including fixture main body, bottom plate, lock sleeve, first expansion sleeve, second expansion sleeve, inner pressure sleeve, sliding sleeve and outer tight nut, the fixture main body is made of small pipe section and big pipe section, the big pipe section is equipped with a lock sleeve, the first expansion sleeve is located in the front end opening of small pipe section, the second expansion sleeve is divided into second guide section and second clamping section from outside to inside, the outer wall of second guide section is slidingly matched with the inner wall of small pipe section, the second clamping section is located in lock sleeve, the outer side of small pipe section is equipped with an inner pressure sleeve, a sliding sleeve and an outer tight nut.The application is to solve the eccentricity of the existing gear hobbing machine's clamping system after clamping parts, clamping eccentricity is enlarged after distance, which can reduce the eccentricity of the parts after clamping, improve the yield of expansion sleeve type gear hobbing fixture.

Description

Technical Field

[0001] This invention relates to the field of tooling and fixture technology, and in particular to a sleeve-type gear hobbing fixture. Background Technology

[0002] The gear hobbing process mainly involves a gear hobbing machine clamping a part in a fixture and rotating it, then using a hob to perform generating cuts on the rotating part. If the workpiece is clamped eccentrically during this process, the large runout during rotation directly affects the gear hobbing tooth profile, causing disordered tooth direction and excessive runout, resulting in defective products and scrapped parts.

[0003] Currently, the clamping system of gear hobbing machines in the industry is often a single expansion sleeve structure. Due to the radial clearance between the part and the fixture, there is always an eccentricity after the part is clamped. The normal clamping eccentricity will be 0.05mm after the distance is magnified. In addition, the hobbing rigidity is not good. The part runs out a lot during gear processing, which can easily lead to problems such as disordered tooth profile and tooth direction. Summary of the Invention

[0004] In order to solve the problem that the clamping system of existing gear hobbing machine tools has an eccentricity after clamping parts, and the clamping eccentricity is amplified by the distance, which easily leads to defective products and scrapped parts, this invention proposes an expansion sleeve type gear hobbing fixture that can reduce the eccentricity after clamping parts and improve the yield.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a sleeve-type gear hobbing clamp, comprising at least a clamp body, a base plate, an anti-loosening sleeve, a first sleeve, a second sleeve, an inner pressure sleeve, a sliding sleeve, and an outer tightening nut. The clamp body is composed of a small pipe section and a large pipe section. The inner diameter of the small pipe section is smaller than that of the large pipe section. A shoulder is formed at the connection between the inner walls of the small pipe section and the large pipe section. The front end of the small pipe section is open and a tapered surface a in the shape of an flared opening is provided on the inner side of the front opening. The rear end of the small pipe section is coaxially connected to the front end of the large pipe section. The rear end of the large pipe section is fixed to the base plate. The large pipe section is provided with an anti-loosening sleeve. The outer wall of the anti-loosening sleeve is slidably connected to the inner wall of the large pipe section. The front end of the anti-loosening sleeve abuts against the shoulder of the hole, and an elastic pad is sandwiched between the rear end and the bottom plate. The inner side of the front opening of the anti-loosening sleeve is provided with a tapered surface b in the shape of a constriction, and the inner side of the rear opening of the anti-loosening sleeve is provided with a positioning tip. The first expansion sleeve is disposed in the front opening of the small pipe section. The first expansion sleeve is divided into a first clamping section and a first guide section from the outside to the inside. The outer wall of the first guide section slides in fit with the inner wall of the small pipe section. The first clamping section is provided with a tapered surface c that matches the tapered surface a in the front opening of the small pipe section. The front end of the first clamping section is provided with a number of strip-shaped first expansion grooves at equal intervals in the circumferential direction. The second expansion sleeve is divided into a second guide section and a second clamping section from the outside to the inside. The outer wall of the second guide section slides with the inner wall of the small tube section. The second clamping section is located inside the anti-loosening sleeve. The second clamping section is provided with a tapered surface d that matches the tapered surface b inside the front opening of the anti-loosening sleeve. The front end of the second clamping section is provided with several strip-shaped second expansion grooves at equal intervals in the circumferential direction. The outer side of the small pipe section is fitted with an inner pressure sleeve, a sliding sleeve and an outer tightening nut; The inner pressure sleeve includes an inner pressure ring and a guide sleeve. The guide sleeve is slidably connected to the small pipe section and the outer wall of the guide sleeve is provided with a positive external thread. The inner pressure ring is fixed to the front end of the guide sleeve and located at the front end of the small pipe section. The inner pressure ring can abut against the front end of the first expansion sleeve and push the first expansion sleeve to move towards the rear end of the clamp body. The sliding sleeve is located behind the inner pressure sleeve and is slidably connected to the small pipe section. The outer wall of the sliding sleeve is provided with reverse external threads. The sliding sleeve and the second guide section of the second expansion sleeve are connected and fixed by several connecting rods. The small pipe section is provided with several strip holes for the connecting rods to pass through. The sliding sleeve and the second expansion sleeve can move synchronously along the axial direction of the small pipe section. The external tightening nut is tubular, with internal threads of opposite directions on the inner sides of both ends. One end of the external tightening nut is screwed into the positive external thread on the guide sleeve, and the other end is screwed into the reverse external thread on the sliding sleeve.

[0006] Preferably, an anti-rotation mechanism is provided between the small tube section of the clamp body and the guide sleeve of the inner pressure sleeve. The anti-rotation mechanism is as follows: a keyway is provided on the outer wall of the small tube section, a flat key is provided in the keyway, the lower part of the flat key is positioned in the keyway, and the upper part protrudes from the keyway. A slide is provided on the inner wall of the guide sleeve that matches the width of the flat key. The slide is arranged along the length direction of the guide sleeve, and the upper part of the flat key is located in the slide and can move along the slide.

[0007] Preferably, the connecting rod is a countersunk bolt, the outer wall of the sliding sleeve is provided with a bolt countersunk hole that matches the countersunk bolt, the second guide section of the second expansion sleeve is provided with a bolt positioning hole that matches the countersunk bolt, and the countersunk bolt passes through the corresponding bolt countersunk hole and the strip hole in sequence and is screwed and fixed on the bolt positioning hole.

[0008] Preferably, the front end of the first expansion sleeve is provided with a number of retraction blocks at equal intervals in the circumferential direction. The number of retraction blocks is the same as the number of first tensioning grooves, and a retraction block is provided between each two adjacent first tensioning grooves. The retraction blocks are located in front of the inner pressure ring of the inner pressure sleeve, and the inner pressure ring can move forward to abut against the retraction blocks.

[0009] Preferably, an annular protective cover is positioned on the front side of the inner pressure ring of the inner pressure sleeve. The annular protective cover is coaxially arranged with the guide sleeve, the inner hole size of the annular protective cover matches the machining shaft, and the retraction block is located inside the annular protective cover.

[0010] Therefore, the present invention has the following beneficial effects: 1. The present invention adopts a double-expansion sleeve structure, which overcomes the problem that the single-expansion sleeve structure has only one annular clamping point after clamping shaft parts, resulting in eccentricity after clamping the parts. The clamping eccentricity is easily amplified by the distance, which can easily lead to defective products and scrapped parts. The double-expansion sleeve structure has two annular clamping points after clamping the parts, which can greatly reduce the eccentricity after clamping the parts, thereby ensuring the yield rate of parts processing; 2. The parts installation and positioning are simple. Although two double-expansion sleeves are set, only one external tightening nut needs to be rotated when installing and positioning the parts; 3. The present invention also sets an anti-loosening sleeve. During the part processing, the anti-loosening sleeve can give the two expansion sleeves a force in the clamping direction to prevent the parts from loosening during processing, and can also further ensure the coaxiality between the parts and the fixture. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the structure of the present invention.

[0012] Figure 2 This is a cross-sectional view of the present invention.

[0013] Figure 3 yes Figure 2 Enlarged view of point a in the middle.

[0014] Figure 4 This is a cross-sectional view of the main body of the present invention.

[0015] Figure 5 This is a cross-sectional view of the anti-loosening sleeve in this invention.

[0016] Figure 6 This is a schematic diagram of the structure of the first expansion sleeve in this invention.

[0017] Figure 7 This is a schematic diagram of the structure of the second expansion sleeve in this invention.

[0018] Figure 8 This is a schematic diagram of the inner pressure sleeve in this invention.

[0019] Figure 9 This is a cross-sectional view of the inner pressure sleeve in this invention.

[0020] Figure 10 This is a schematic diagram of the sliding sleeve in this invention.

[0021] Figure 11 This is a cross-sectional view of the external tightening nut in this invention.

[0022] Figure 12 This is a schematic diagram of the retraction stop block in this invention.

[0023] Figure 13 This is a schematic diagram of the structure of the annular protective cover in this invention.

[0024] 1: Main body; 101: Small pipe section; 102: Large pipe section; 103: Shoulder; 104: Conical surface a; 105: Strip hole; 106: Keyway; 2: Base plate; 3: Anti-loosening sleeve; 301: Conical surface b; 4: First expansion sleeve; 401: First clamping section; 402: First guide section; 403: Conical surface c; 404: First tensioning groove; 5: Second expansion sleeve; 501: Second guide section; 502: 503: Second clamping section; 504: Tapered surface d; 505: Second tension groove; 6: Inner pressure sleeve; 606: Inner pressure ring; 607: Guide sleeve; 608: Forward external thread; 609: Slide rail; 700: Sliding sleeve; 700: Reverse external thread; 8: External tightening nut; 9: Elastic pad; 10: Positioning center; 11: Connecting rod; 12: Flat key; 13: Retraction stop; 14: Annular protective cover; 15: Machining shaft. Detailed Implementation

[0025] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0026] A type of expansion sleeve gear hobbing clamp, such as Figures 1 to 3 As shown, it includes at least the clamp body 1, base plate 2, anti-loosening sleeve 3, first expansion sleeve 4, second expansion sleeve 5, inner pressure sleeve 6, sliding sleeve 7, and outer tightening nut 8.

[0027] The clamp body 1 is composed of a small pipe section 101 and a large pipe section 102, such as Figure 4 As shown, the inner diameter of the small pipe section 101 is smaller than the inner diameter of the large pipe section 102. A shoulder 103 is formed at the connection between the inner walls of the small pipe section 101 and the large pipe section 102. The front end of the small pipe section 101 is open and a tapered surface a104 in the shape of an flared opening is provided on the inner side of the front opening. The rear end of the small pipe section 101 is coaxially connected to the front end of the large pipe section 102. The rear end of the large pipe section 102 is fixed to the base plate 2. The base plate 2 is a circular plate and is coaxially fixed to the fixture body 1. Six installation positioning holes are provided at equal intervals around the edge of the base plate 2.

[0028] An anti-loosening sleeve 3 is installed inside the large pipe section 102, such as Figure 5 As shown, the outer wall of the anti-loosening sleeve 3 is slidably connected to the inner wall of the large pipe section 102. The front end of the anti-loosening sleeve 3 abuts against the shoulder 103, and an elastic pad 9 is sandwiched between the rear end and the bottom plate 2. The inner side of the front opening of the anti-loosening sleeve 3 is provided with a tapered surface b301 in the shape of a constriction, and the inner side of the rear opening of the anti-loosening sleeve 3 is provided with a positioning tip 10.

[0029] The first expansion sleeve 4 is located inside the front opening of the small pipe section 101. The first expansion sleeve 4 is divided into a first clamping section 401 and a first guide section 402 from the outside to the inside, as follows: Figure 6As shown, the outer wall of the first guide section 402 is slidably engaged with the inner wall of the small tube section 101. The first clamping section 401 is provided with a tapered surface c403 that matches the tapered surface a104 inside the front opening of the small tube section 101. The front end of the first clamping section 401 is provided with eight strip-shaped first tensioning grooves 404 at equal intervals.

[0030] The second expansion sleeve 5 is divided into a second guide section 501 and a second clamping section 502 from the outside to the inside, as follows: Figure 7 As shown, the outer wall of the second guide section 501 is slidably fitted with the inner wall of the small tube section 101. The second clamping section 502 is located inside the anti-loosening sleeve 3. The second clamping section 502 is provided with a tapered surface d503 that matches the tapered surface b301 in the front opening of the anti-loosening sleeve 3. The front end of the second clamping section 502 is provided with eight strip-shaped second tensioning grooves 504 at equal intervals in the circumferential direction.

[0031] The outer side of the small pipe section 101 is fitted with an inner pressure sleeve 6, a sliding sleeve 7 and an outer tightening nut 8.

[0032] The inner pressure sleeve 6 includes an inner pressure ring 601 and a guide sleeve 602, such as Figure 8 , Figure 9 As shown, the guide sleeve 602 is slidably connected to the small pipe section 101 and the outer wall of the guide sleeve 602 is provided with a positive external thread 603. The inner pressure ring 601 is fixed to the front end of the guide sleeve 602 and is located at the front end of the small pipe section 101. The inner pressure ring 601 can abut against the front end of the first expansion sleeve 4 and push the first expansion sleeve 4 to move towards the rear end of the clamp body 1.

[0033] An anti-rotation mechanism is provided between the small pipe section 101 of the clamp body 1 and the guide sleeve 602 of the inner pressure sleeve 6. The anti-rotation mechanism is as follows: a keyway 106 is provided on the outer wall of the small pipe section 101, and a flat key 12 is provided in the keyway 106. The lower part of the flat key 12 is positioned in the keyway 106, and the upper part protrudes out of the keyway 106. A slide 604 matching the width of the flat key 12 is provided on the inner wall of the guide sleeve 602. The slide 604 is arranged along the length direction of the guide sleeve 602, and the upper part of the flat key 12 is located in the slide 604 and can move along the slide 604.

[0034] The sliding sleeve 7 is located behind the inner pressure sleeve 6 and is slidably connected to the small pipe section 101. The outer wall of the sliding sleeve 7 is provided with a reverse external thread 701, such as... Figure 10 As shown, the sliding sleeve 7 and the second guide section 501 of the second expansion sleeve 5 are connected and fixed by four connecting rods 11. The small tube section 101 is provided with four strip holes 105 for the connecting rods 11 to pass through. The four strip holes 105 correspond one-to-one with the four connecting rods 11. The sliding sleeve 7 and the second expansion sleeve 5 can move synchronously along the axial direction of the small tube section 101.

[0035] The connecting rod 11 is a countersunk bolt. The outer wall of the sliding sleeve 7 is provided with a bolt countersunk hole that matches the countersunk bolt. The second guide section 501 of the second expansion sleeve 5 is provided with a bolt positioning hole that matches the countersunk bolt. The countersunk bolt passes through the corresponding bolt countersunk hole and the strip hole 105 in sequence and is screwed and fixed on the bolt positioning hole.

[0036] The external tightening nut 8 is tubular, such as Figure 11 As shown, the outer wall of the external tightening nut 8 is provided with a hexagonal positioning part for wrench locking and positioning. The inner sides of both ends of the external tightening nut 8 are provided with internal threads with opposite thread directions. One end of the external tightening nut 8 is screwed into the positive external thread 603 on the guide sleeve 602, and the other end is screwed into the reverse external thread 701 on the sliding sleeve 7.

[0037] The front end of the first expansion sleeve 4 is circumferentially spaced with several retraction blocks 13, such as... Figure 12 As shown, the number of retraction blocks 13 is the same as the number of first tensioning grooves 404, and a retraction block 13 is provided between each two adjacent first tensioning grooves 404; the retraction block 13 is located in front of the inner pressure ring 601 of the inner pressure sleeve 6, and the inner pressure ring 601 can move forward to abut against the retraction block 13.

[0038] An annular protective cover 14 is positioned on the front side of the inner pressure ring 601 of the inner pressure sleeve 6. The annular protective cover 14 is coaxially arranged with the guide sleeve 602, and the inner hole size of the annular protective cover 14 matches the machining shaft 15. The retraction stop block 13 is located inside the annular protective cover 14. The annular protective cover 14 effectively prevents metal chips generated during machining from entering the fixture.

[0039] In use, the invention is first installed and positioned on the gear hobbing machine. Then, one end of the machining shaft 15 is inserted from the front end of the fixture body 1. The machining shaft 15 passes through the annular protective cover 14, the first expansion sleeve 4, and the second expansion sleeve 5 in sequence, and finally abuts against the positioning tip 10. Then, the outer tightening nut 8 is rotated. Since the inner sides of the two ends of the outer tightening nut 8 are internal threads with opposite thread directions, the rotation of the outer tightening nut 8 causes the inner pressure sleeve 6 and the sliding sleeve 7 to move towards the inner side of the outer tightening nut 8. The inner pressure sleeve 6 and the sliding sleeve 7 approach each other, and the inner pressure ring 601 of the inner pressure sleeve 6 pushes the first expansion sleeve 4 to move towards the rear end of the fixture body 1. The sliding sleeve 7 drives the second expansion sleeve 5 to move towards the front end of the fixture body 1 through the connecting rod 11. Finally, the tapered surface c403 on the first expansion sleeve 4 engages with the tapered surface a104 inside the opening at the front end of the small pipe section 101 to clamp the machining shaft 15, and the tapered surface d503 on the second expansion sleeve 5 engages with the tapered surface b301 inside the opening at the front end of the anti-loosening sleeve 3 to clamp the machining shaft 15. At this time, the machining shaft 15 is clamped by two expansion sleeves, with two annular clamping points, which can greatly reduce the eccentricity of the machining shaft 15 after clamping, thereby ensuring the yield rate of subsequent part processing.

[0040] Furthermore, the present invention includes an anti-loosening sleeve 3. During the machining process, the end of the machining shaft 15 not held by the fixture will also be abutted by a tip. Therefore, the machining shaft 15 will continuously be subjected to a force toward the rear of the fixture body 1. If the machining shaft 15 becomes loose between the expansion sleeve and the expansion sleeve, the machining shaft 15 will transmit the force to the positioning tip 10 inside the anti-loosening sleeve 3. The positioning tip 10 moves backward under the force, squeezing the elastic pad 9 and pulling the anti-loosening sleeve 3 backward. During the backward movement of the anti-loosening sleeve 3, it pulls the second expansion sleeve 5 backward while simultaneously clamping the machining shaft 15 again through the action of the tapered surface b301 in the front opening of the anti-loosening sleeve 3 and the tapered surface d503 on the second expansion sleeve 5. At the same time, the backward movement of the second expansion sleeve 5 causes the sliding sleeve 7, the outer tightening nut 8, and the inner pressure sleeve 6 to move backward. The inner pressure ring 601 of the inner pressure sleeve 6 pushes the first expansion sleeve 4 toward the rear end of the fixture body 1 again. Finally, both expansion sleeves clamp the machining shaft 15 again. The anti-loosening sleeve 3 effectively prevents the parts from coming loose during processing, ensuring the safety of the parts during processing and further ensuring the coaxiality of the processing shaft 15 and the fixture body 1.

[0041] After processing is completed, simply rotate the outer tightening nut 8 in the opposite direction to unlock and replace the processing shaft 15.

Claims

1. A type of expansion sleeve gear hobbing fixture, characterized in that: It includes at least the clamp body (1), base plate (2), anti-loosening sleeve (3), first expansion sleeve (4), second expansion sleeve (5), inner pressure sleeve (6), sliding sleeve (7) and outer tightening nut (8). The main body (1) of the clamp is composed of a small pipe section (101) and a large pipe section (102). The inner diameter of the small pipe section (101) is smaller than that of the large pipe section (102). A shoulder (103) is formed at the connection between the inner walls of the small pipe section (101) and the large pipe section (102). The front end of the small pipe section (101) is open and a tapered surface a (104) in the shape of an flared opening is provided on the inner side of the front opening. The rear end of the small pipe section (101) is coaxially connected to the front end of the large pipe section (102). The rear end of the large pipe section (102) is fixed to the base plate (2). The large pipe section (102) is provided with an anti-loosening sleeve (3). The outer wall of the anti-loosening sleeve (3) is slidably connected to the inner wall of the large pipe section (102). The front end of the anti-loosening sleeve (3) abuts against the shoulder (103), and an elastic pad (9) is sandwiched between the rear end and the bottom plate (2). The inner side of the front opening of the anti-loosening sleeve (3) is provided with a tapered surface b (301) in the shape of a constriction, and the inner side of the rear opening of the anti-loosening sleeve (3) is provided with a positioning tip (10). The first expansion sleeve (4) is located in the front opening of the small pipe section (101). The first expansion sleeve (4) is divided into a first clamping section (401) and a first guide section (402) from the outside to the inside. The outer wall of the first guide section (402) is slidably engaged with the inner wall of the small pipe section (101). The first clamping section (401) is provided with a tapered surface c (403) that matches the tapered surface a (104) in the front opening of the small pipe section (101). The front end of the first clamping section (401) is provided with a number of strip-shaped first expansion grooves (404) at equal intervals in the circumferential direction. The second expansion sleeve (5) is divided into a second guide section (501) and a second clamping section (502) from the outside to the inside. The outer wall of the second guide section (501) slides with the inner wall of the small tube section (101). The second clamping section (502) is located inside the anti-loosening sleeve (3). The second clamping section (502) is provided with a tapered surface d (503) that matches the tapered surface b (301) in the front opening of the anti-loosening sleeve (3). The front end of the second clamping section (502) is provided with a number of strip-shaped second expansion grooves (504) at equal intervals in the circumferential direction. The outer side of the small pipe section (101) is fitted with an inner pressure sleeve (6), a sliding sleeve (7) and an outer tightening nut (8); The inner pressure sleeve (6) includes an inner pressure ring (601) and a guide sleeve (602). The guide sleeve (602) is slidably connected to the small pipe section (101) and the outer wall of the guide sleeve (602) is provided with a positive external thread (603). The inner pressure ring (601) is fixed to the front end of the guide sleeve (602) and located at the front end of the small pipe section (101). The inner pressure ring (601) can abut against the front end of the first expansion sleeve (4) and push the first expansion sleeve (4) to move towards the rear end of the clamp body (1). The sliding sleeve (7) is located behind the inner pressure sleeve (6) and is slidably connected to the small pipe section (101). The outer wall of the sliding sleeve (7) is provided with a reverse external thread (701). The sliding sleeve (7) and the second guide section (501) of the second expansion sleeve (5) are connected and fixed by several connecting rods (11). The small pipe section (101) is provided with several strip holes (105) for the connecting rods (11) to pass through. The sliding sleeve (7) and the second expansion sleeve (5) can move synchronously along the axial direction of the small pipe section (101). The external tightening nut (8) is tubular, and the inner sides of both ends of the external tightening nut (8) are provided with internal threads with opposite thread directions. One end of the external tightening nut (8) is screwed into the positive external thread (603) on the guide sleeve (602), and the other end is screwed into the reverse external thread (701) on the sliding sleeve (7). An anti-rotation mechanism is provided between the small pipe section (101) of the fixture body (1) and the guide sleeve (602) of the inner pressure sleeve (6). The anti-rotation mechanism is as follows: a keyway (106) is provided on the outer wall of the small pipe section (101), and a flat key (12) is provided in the keyway (106). The lower part of the flat key (12) is positioned in the keyway (106), and the upper part protrudes from the keyway (106). A slide (604) matching the width of the flat key (12) is provided on the inner wall of the guide sleeve (602). The slide (604) is set along the length direction of the guide sleeve (602), and the upper part of the flat key (12) is located in the slide (604) and can move along the slide (604).

2. The expanding sleeve type gear hobbing fixture according to claim 1, characterized in that: The connecting rod (11) is a countersunk bolt. The outer wall of the sliding sleeve (7) is provided with a bolt countersunk hole that matches the countersunk bolt. The second guide section (501) of the second expansion sleeve (5) is provided with a bolt positioning hole that matches the countersunk bolt. The countersunk bolt passes through the corresponding bolt countersunk hole and the strip hole (105) in sequence and is screwed and fixed on the bolt positioning hole.

3. The expanding sleeve type gear hobbing fixture according to claim 1, characterized in that: The front end of the first expansion sleeve (4) is circumferentially spaced with a number of retraction blocks (13). The number of retraction blocks (13) is the same as the number of the first tensioning grooves (404). A retraction block (13) is provided between two adjacent first tensioning grooves (404). The retraction block (13) is located in front of the inner pressure ring (601) of the inner pressure sleeve (6). The inner pressure ring (601) can move forward to abut against the retraction block (13).

4. The expanding sleeve type gear hobbing fixture according to claim 3, characterized in that: An annular protective cover (14) is positioned on the front side of the inner pressure ring (601) of the inner pressure sleeve (6). The annular protective cover (14) is coaxially arranged with the guide sleeve (602). The inner hole size of the annular protective cover (14) matches the machining shaft (15). The retraction block (13) is located inside the annular protective cover (14).

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