Method for processing long and deep hole of shaft by common lathe pushing boring

Abstract

The application discloses a processing method for boring slender deep holes of shafts on a general lathe, and has excellent cooling and lubricating effects, high processing quality and high processing efficiency. The application adopts the following technical scheme: a blade group tooth boring tool is made by using super-hard high-speed steel as a tool head material, distributing 20 degrees along a chip groove bottom, and making end blade helical teeth Z greater than or equal to 4; a tool bar is connected with a lathe tailstock through a stepped shaft, a cylindrical milling flat surface of a connecting part is pressed, and a tool head is connected with a rectangular body thread at a front end tool handle part of the tool bar; four cooling holes are made in the tool head according to the diameter of the internal cooling hole of the tool bar being in the range of Phi 4-Phi 7; the four cooling holes are connected with the cooling hole of the tool bar; during the processing of the slender hole, the chuck and the center frame are installed on the lathe, the cooling hose is connected with the segment tail's dog tooth, the cooling liquid directly enters the boring cooling area for cooling through the shaft control tool handle center Phi 7 cooling hole and the cooling hole of the tool head, and the cutting chip is timely discharged by means of the dragging of the tool holder.

Description

Technical Field

[0001] This invention relates to a method for deep hole enlargement machining of shaft parts using a conventional lathe with a special push boring head and tool holder, especially for parts with a large length-to-diameter ratio (L / D > 16). Background Technology

[0002] Shafts with a length-to-diameter ratio greater than 20–25 (i.e., L / d ≥ 20–25) are called slender shafts. These parts are generally machined on lathes. During turning, due to their poor rigidity, slender shafts are prone to bending deformation under cutting forces and heat. This disrupts the accuracy of the relative movement between the tool and the workpiece, resulting in a shaft that is thicker in the middle and thinner at both ends, severely affecting machining accuracy. Furthermore, bending deformation can cause vibration in the machining system, affecting the surface finish. Under the influence of cutting forces and gravity, transversely positioned slender shafts are easily bent or even unstable. Due to their poor rigidity, improper clamping during turning can easily lead to bending deformation and vibration under cutting forces and gravity, affecting machining accuracy and surface roughness. Slender shafts also have poor thermal diffusion, resulting in significant linear expansion under cutting heat. If both ends of the shaft are fixed supports, the workpiece will bend due to elongation. Because of the shaft's length, a single pass takes a long time, leading to significant tool wear and affecting the geometric accuracy of the part. When machining slender shafts, the use of a follower post can affect machining accuracy if the pressure exerted by the two support blocks on the workpiece is inappropriate. Insufficient pressure or lack of contact renders them ineffective and fails to improve the workpiece's rigidity. Excessive pressure forces the workpiece against the cutting tool, increasing the depth of cut and resulting in a smaller diameter. As the follower post moves further, the support blocks detach from the workpiece at the smaller diameter outer circle, causing the cutting force to push the workpiece outwards, reducing the depth of cut and increasing the diameter. Then, the follower post moves back to the larger diameter circle, pressing the workpiece against the cutting tool again, reducing the diameter. This continuous, regular change results in a slender workpiece being machined into a "bamboo-like" shape. Poor rigidity in the machine tool, workpiece, and tooling system makes machining difficult, hindering the achievement of good surface roughness and geometric accuracy. Drilling large-diameter deep holes on lathes is also problematic, especially for workpieces such as hollow rods, hollow slender shafts, and machine tool spindles. The risks of using twist drills for these holes include drill bit damage, breakage, and difficulty in removing the drill bit if it falls out of the hole. Furthermore, the difficulty in chip removal and the need for repeated chip removal operations make cooling and lubrication difficult. The large drill diameter and high axial cutting force also hinder automatic feed using a lathe's large slide. Therefore, most people without the necessary operating skills are deterred from using this method.

[0003] Deep holes are defined as holes with a length-to-diameter ratio greater than 5. However, in practical work, ultra-deep holes with a length-to-diameter ratio greater than 100 are frequently encountered. Based on the dimensional requirements of the workpiece, these generally fall under the category of ultra-deep hole machining, which presents significant manufacturing challenges. Even machining on a dedicated deep drilling machine using external chip removal deep drilling presents considerable difficulties. Therefore, machining on a conventional lathe also presents certain challenges, mainly in the following aspects: workpiece positioning, selecting appropriate long-rod cutting tools according to the manufacturing requirements of the conventional lathe, chip removal and cooling treatment, and drilling and cutting processes. The machining of slender hole components is currently one of the most difficult types of parts to manufacture in mechanical equipment. Machining slender holes in shaft parts is particularly challenging in machining. In aerospace hydraulic products, piston rods often have deep hole structures, and batch processing of such parts often requires specialized equipment. This is because the dimensional requirements for machining these slender hole components are quite stringent. Production workers rely on specialized equipment to complete the operation, making it a relatively complex manufacturing process. For ordinary machine tools, machining slender holes presents significant manufacturing challenges, requiring the use of conventional machine tool drilling equipment and strict control of cutting processes, adhering strictly to production requirements. Some factories lack specialized machinery for auxiliary processing; however, the technology for machining slender holes on ordinary machine tools needs continuous improvement. Utilizing ordinary lathes for deep hole machining of shaft parts, thereby improving manufacturing efficiency, is of great significance in addressing practical production bottlenecks.

[0004] For certain products involving stressed shaft components, the surface quality of the inner bore has a significant impact on the fatigue strength of the component. While drilling larger bores can be performed using a damping tool holder for precision boring to improve the surface quality, for components with elongated bore structures, the surface quality after drilling is often unsatisfactory, and even precision boring with a damping tool holder cannot solve the problem. This ultimately affects the component's fatigue strength performance.

[0005] In hole machining, the depth-to-diameter ratio determines the rigidity of the machining process and the characteristics of the tool structure. A larger diameter-to-diameter ratio (L / D) reduces the rigidity of the machining system and increases the difficulty of chip removal and cooling. Because the cutting process of long and narrow holes cannot be directly observed, when using a conventional lathe for this purpose, the cutting process can only be judged by experience and cutting sounds. Furthermore, the cutting heat is difficult to dissipate. While 80% of the cutting heat is typically carried away by the chips during general cutting, only 40% is carried away in the machining of long and narrow holes. The tool accounts for a larger proportion of the cutting heat, which diffuses slowly, leading to overheating of the cutting edge and necessitating effective cooling. However, conventional cooling methods often fail to deliver coolant deep into the long and narrow holes. The difficulty in dissipating cutting heat during long and narrow hole machining causes the tool temperature to rise, resulting in accelerated tool wear and reduced machining efficiency and quality. Due to the long and narrow structure of the machined hole, the chip removal path is long, making chip removal difficult and prone to clogging and tool breakage. Therefore, the length and shape of the chips need to be controlled. The machining system suffers from poor rigidity. Due to limitations in hole diameter, the tool holder is thin and long, resulting in low rigidity and a tendency to vibrate and deviate during hole machining. Misalignment in deep holes is often caused by issues with axial force and the rigidity of the drill bit. While deep cutting techniques are used in manufacturing slender holes, rapid cooling is crucial to prevent reactions and accidents caused by extreme temperature changes. After drilling, debris must be quickly removed to prevent blockages and ensure a smoother manufacturing process, improving efficiency. In manufacturing slender hole components, cooling and chip removal must be prioritized and managed effectively; otherwise, the sequence and smoothness of the entire operation will be affected.

[0006] Currently, when machining slender holes on ordinary lathes, the machines typically lack high-pressure equipment, making it difficult to deliver coolant deep into the holes for cooling. Achieving high-quality machining of slender shaft parts is generally challenging, primarily due to the workpiece's slender shape and poor rigidity. During turning, twisted, prismatic, or bamboo-like shapes may appear, making it difficult to maintain the workpiece's ovality and taper. Machining slender holes on ordinary lathes requires timely cooling of the cutting area and prompt chip removal to ensure the machining process can continue; otherwise, blockages may occur. Under current conventional cooling methods, cutting fluid is prohibited from entering the cutting area, limiting its effectiveness in chip removal and cooling, thus restricting its application. Considering the workpiece's dimensions (L / D ≈ 70), this constitutes an ultra-deep hole, making machining extremely difficult, even on a dedicated deep-hole drilling machine with external chip removal. Machining on an ordinary lathe presents the following main difficulties:

[0007] (1) Precise positioning of the workpiece

[0008] The clamping and positioning of the workpiece directly affects the drilling accuracy. Besides the rigidity of the drill bit and the magnitude of the axial force, the clamping and positioning of the workpiece is also a major contributing factor to the tendency for deep hole drilling to deviate. Therefore, it is necessary to design a dedicated fixture based on the workpiece's dimensional requirements, combined with the specific machining equipment and process methods, to solve the workpiece clamping and positioning problem.

[0009] (2) For drilling ultra-deep holes using long-rod cutting drills suitable for ordinary lathes, suitable long-rod drills are essential. However, it is difficult to find suitable ultra-deep hole drills on the market that meet the required machining dimensions.

[0010] (3) Cooling and chip removal issues during processing

[0011] Boring tools used in machining centers, in terms of their cutting parts, are not fundamentally different from external turning tools. However, boring on machining centers typically employs cantilever machining, thus requiring different cutting conditions for the boring tool. Boring tools come in various types. Based on the number of cutting edges, they can be divided into single-edge boring tools and double-edge boring tools. The shank and cutting part of this type of boring tool are integrated, with the cutting part primarily made of carbide. It has only one cutting edge, a compact and simple structure, small size, and is easy to manufacture. It can bore various small holes, blind holes, and stepped holes. If mounted on a universal tool post or a rotary table slide, it can bore larger diameter holes and end faces. However, single-edge boring tools have poor rigidity and are prone to vibration during cutting. The bore diameter must be adjusted by changing the tool overhang, which is cumbersome and inefficient. Deep hole machining refers to machining where the ratio of hole depth to lightness is between 5 and 30. The depth presents challenges in chip removal, cooling and lubrication, and difficulty in observing the surface quality. Furthermore, cutting tools wear easily, and the machined surface is easily scratched by chips, making it difficult to guarantee surface quality. Thin-walled deep-hole cylindrical parts are prone to center hole deviation, making it impossible to guarantee the straightness of the hole shape or causing deformation. In the drilling process of ultra-deep holes, ensuring effective cooling of the cutting area and continuous chip removal is crucial for the continuous machining process, preventing drill jamming, and ensuring the lifespan of the drill bit. Conventional cooling methods are unsuitable in ultra-deep hole machining because cutting fluid cannot be directly injected into the cutting area, and the cooling and chip removal effects are not guaranteed. In conclusion, the machining of ultra-deep, slender holes has always been a difficult problem in machining. Summary of the Invention

[0012] The purpose of this invention is to address the problems existing in the prior art by providing a tool and process method for precision machining of slender holes that offers excellent cooling and lubrication effects, high machining quality and efficiency, and solves the guiding problem in machining slender holes.

[0013] The technical solution adopted by this method to solve the technical problem is as follows: a method for machining slender deep holes of shafts using a conventional lathe, characterized in that: the method includes: design of the tool head, design of the tool holder, cooling method, and reasonable chip removal method; the length of the cutting shaft is >65; the tool head design: the tool head material is made of ultra-hard high-speed steel with high hardness, high wear resistance and high high temperature hardness, and is subjected to quenching at 1220-1250℃ + tempering at 550-600℃ to achieve a Rockwell hardness of 66-69; according to the diameter of the slender deep hole of the shaft, a cutting edge tip rake angle ≤10°, a cutting edge tip back helix angle ≤14°, a cutting edge rotation angle ≤30° in the direction of the cutting shaft generatrix, and a chip groove cutting shaft with a chip groove bottom inclination ≥20°, and a cutting edge tip angle ≤2° and a cutting core tip angle ≤6° at the axial center, to make a guiding chip removal cutting edge group tooth boring tool with a cutting edge helical tooth number Z≥4;

[0014] The tool holder is made of high-strength tempered steel with a hardness greater than HRC35-40. The diameter of the tool holder is the cutting edge diameter minus 4-6mm. It is coaxially connected to the chip groove cutting edge. The tool holder part at the front end of the tool holder is threaded to the tool head in a rectangular shape. The tool holder end has a center hole. The center of the tool holder has an axial cooling hole that connects to the cooling hole of the chip groove cutting edge. The tool holder is connected to the lathe tailstock in a stepped shaft manner. The connecting part is cylindrical for milling flat surfaces. The working length of the flat milling surface is ≥ 25 times the diameter of the tool head.

[0015] Cooling method: The diameter of the tool holder is adjusted within the range of Φ4-Φ7 according to the diameter of its internal cooling holes. The axial cooling holes inside the tool holder are connected to at least 4 chip groove cutting axis cooling holes inside the tool head. When machining slender holes, the slender deep hole machining parts of the shaft type are mounted on the lathe guide rail using a lathe chuck and center rest. The cooling hose is connected to the toothed thread of the axial cooling hole at the end of the tool holder section. The coolant enters the boring cooling area directly through the axial cooling hole at the center of the shaft control tool holder and the chip groove cutting axis cooling holes of the tool head for cooling. The tool holder is fixed on the lathe tool post. The boring chips are pushed by the drag of the lathe tool post and the follow post. The chip grooves of the cutting axis discharge the broken, rolled, and shattered chips in time.

[0016] Compared with other hole processing technologies at present, the present invention has the following advantages:

[0017] To address the cooling issue during machining, this invention incorporates a Φ7 cooling hole inside the tool shank and another Φ7 cooling hole on the tool head shank connected to the tool shank. A 4-Φ2.5 hole on the cutting edge connects to the Φ7 cooling hole on the shank. During machining, coolant directly enters the cooling area through the cooling holes in the tool shank and tool head, achieving both cooling and lubrication. The tool shank is connected to the lathe tailstock via a stepped shaft, with the connecting part milling a flat surface on a cylindrical surface. The working length of the flat milling surface is ≥ 25 times the diameter of the tool head, avoiding the influence of deviation during deep hole machining. Based on the workpiece's dimensional requirements and specific machining equipment, the tool shank is fixed to the lathe tool post, and the boring and chip removal process is achieved by dragging the lathe tool post. This eliminates the need for specialized fixtures, solving the problems of workpiece clamping and positioning, and the easy bending deformation of slender shafts, which causes vibration and instability in the machining system and affects the surface finish of the parts. This fundamentally ensures the cylindricity of the workpiece. The lathe chuck and center rest for machining slender, deep-hole shafts are mounted on the lathe guide rails, overcoming the poor rigidity of slender shafts.

[0018] This invention closely links chip separation, chip curling, and chip breaking during the cutting process. It employs a guided chip-removing toothed boring bar with a multi-tooth cutting edge to reduce the chip volume coefficient (the ratio of cutting volume to the volume of metal removed). An axial cooling hole connected to the cooling hole on the chip groove cutting edge shaft is incorporated at the center of the tool holder, ensuring effective cooling of the cutting area and continuous chip removal. This stabilizes the cutting process and avoids sudden and irregular chip initiation, as well as the drawbacks of conventional cooling methods in ultra-deep hole machining where the cutting fluid cannot be directly injected into the cutting area, resulting in inconsistent cooling and chip removal effects. By using a cutting edge tip angle of ≤6°, a guided chip-removing toothed boring bar with Z≥4 helical teeth on the end edge is manufactured. The tool and tool holder are then used on a conventional lathe for semi-finishing of slender holes, improving the machining quality and efficiency of slender holes.

[0019] This invention addresses the problems of high aspect ratio, thin and long tool holders, low rigidity, and susceptibility to vibration in slender holes, which can lead to hole misalignment and affect machining accuracy and production efficiency. During hole reaming, a four-flute tool with a guided chip-removing toothed boring bar is used, guided by the original hole. Utilizing a stepped shaft tool holder with sufficient rigidity and a corrective function during push boring, the guiding problem in machining slender holes is effectively solved. Compared to single drilling, push boring after drilling can correct existing defects in the hole, such as roundness and straightness errors, thereby achieving good geometric accuracy and surface roughness. Generally, the hole accuracy after push boring can reach IT10-IT11, and the surface roughness Ra can reach 1.6-3.2. Attached Figure Description

[0020] Figure 1This is a schematic diagram of the push boring bar and head cutter for deep hole machining of shaft parts, which are specific to this invention;

[0021] Figure 2 yes Figure 1 Left view;

[0022] Figure 3 yes Figure 1 AA section view;

[0023] Figure 4 This is a schematic diagram of a push boring bar;

[0024] Figure 5 This is a schematic diagram of a shaft-type part with a large length-to-diameter ratio (L / D > 16) and a deep hole to be machined. Detailed Implementation

[0025] See Figures 1-5 According to the present invention, the method includes: design of the cutting head, design of the cutting shank, cooling method, and reasonable chip removal method. The cutting head design involves using ultra-hard high-speed steel with high hardness, high wear resistance, and high high-temperature hardness as the cutting head material. The cutting head is quenched at 1220-1250℃ and tempered at 550-600℃ to achieve a Rockwell hardness of 66-69. Based on the diameter of the shaft-type slender deep-hole machining parts, the cutting head is manufactured with a rake angle ≤10°, a back helix angle ≤14°, a cutting edge rotation angle ≤30° in the direction of the cutting axis generatrix, and a uniformly distributed chip groove cutting axis with a chip groove bottom inclination ≥20°. The cutting edge tip angle is ≤2°, and the core tip angle at the axial center is ≤6°, resulting in a guiding chip removal cutting edge group boring tool with Z≥4 helical teeth at the end of the cutting edge.

[0026] The tool holder is made of high-strength tempered steel with a hardness greater than HRC35-40. The diameter of the tool holder is the cutting edge diameter minus 4-6mm. It is coaxially connected to the chip groove cutting edge. The tool holder part at the front end of the tool holder is threaded to the tool head in a rectangular shape. The tool holder end has a center hole. The center of the tool holder has an axial cooling hole that connects to the cooling hole of the chip groove cutting edge. The tool holder is connected to the lathe tailstock in a stepped shaft manner. The connecting part is cylindrical for milling flat surfaces. The working length of the flat milling surface is ≥ 25 times the diameter of the tool head.

[0027] Cooling method: The diameter of the tool holder is adjusted within the range of Φ4-Φ7 according to the diameter of its internal cooling holes. The axial cooling holes inside the tool holder are connected to at least 4 chip groove cutting axis cooling holes inside the tool head. When machining slender holes, the slender deep hole machining parts of the shaft type are mounted on the lathe guide rail using a lathe chuck and center rest. The cooling hose is connected to the toothed thread of the axial cooling hole at the end of the tool holder section. The coolant enters the boring cooling area directly through the axial cooling hole at the center of the shaft control tool holder and the chip groove cutting axis cooling holes of the tool head for cooling. The tool holder is fixed on the lathe tool post. The boring chips are pushed by the drag of the lathe tool post and the follow post. The chip grooves of the cutting axis discharge the broken, rolled, and shattered chips in time.

[0028] The cutting head is used to machine slender holes with a diameter Φ≥34, a depth of machining >500, and a length-to-diameter ratio L / D>10. The cutting edge diameter φ≥34 and the cutting axis length ≥65.

[0029] This cutting head is designed for machining slender holes with a diameter Φ≥34+0.15 0 and a machining depth >500, with an L / D >10. Its technical parameters are as follows: cutting edge diameter φ≥34.050-0.01, coaxiality with the shank within 0.01; radial cutting edge angle ≤2°, runout with the shank within 0.01; number of cutting edges Z≤4; cutting edge angle ≤10°; at least 4 chip groove cutting edge cooling holes Φ≤2.5; cylindrical diameter Φ≥30 and length ≥20 at the connection between the chip groove cutting edge and the cutting head shank; milling thickness ≥27 and length ≥18 on the flat surface of the connecting cylindrical part; the shank is connected to the tool holder by a rectangular 20×12 / 2 line, and positioned by an outer circle with a diameter Φ≥20.5, surface roughness Ra0.8, and an outer circle with a diameter Φ17-0.01-0.02.

[0030] The axial cutting edge angle of the cutting edge is ≤6° with a roughness of Ra0.4. The cooling holes at the cutting edge of the cutting head are Φ≤2.5. The length of the cutting edge of the cutting head is ≥65. The cutting edge rotation angle is ≤30°. The cylindrical diameter of the connecting part between the cutting edge and the shank is Φ≥30 and the length is ≥20. The cylindrical thickness of the connecting part is ≥27 and the length is ≥18. The flat surface is connected to the tool holder by a rectangular 20×12 / 2 line. The outer circle with a diameter of Φ≥20.5-0.01-0.02 and a roughness of Ra0.8 and an outer circle with a diameter of Φ17-0.01-0.02 are used for positioning. The dimensions of the rectangular 20×12 / 2 line are: tooth tip diameter Φ≥20-0.05-0.1 and roughness of Ra1.6, tooth root diameter Φ≥17.5-0.05-0.15, tooth spacing ≥3.2, and tooth pitch ≤6.

[0031] The tool holder is made of 30CrMnSiA material with a hardness of HRC35-40. It is used in conjunction with the tool head. The working part of the tool holder has a diameter Φ≥300 and a length ≥555; the connecting part has a diameter Φ≥25 and a length ≥80. The inner diameter holes for locating the tool holder have diameters ≥20.5 and lengths ≥16, and diameters Φ≥17 and lengths ≥11, respectively. The central axial cooling hole of the tool holder has a diameter Φ≥7.

[0032] The tool holder is connected to the chip groove cutting head via a rectangular 20×12 / 2 line. The dimensions of the rectangular 20×12 / 2 line are: tooth tip diameter Φ≥20, tooth root diameter Φ≥17.5, spacing ≥3.2, and tooth pitch ≥6.

[0033] This tool holder is used in conjunction with the tool head. The working part of the tool holder has a diameter Φ≥300-0.05 and a length ≥555. The connecting part has a diameter Φ≥25-0.01-0.02 and a length ≥80. The hole dimensions for connecting the tool holder to the positioning inner diameter are ≥Φ20.5+0.0270, roughness Ra1.6, and length ≥16, and Φ≥17+0.0270, roughness Ra1.6, and length 11, respectively. The tool holder has a cooling hole with a diameter Φ≥7 at its center. The tool holder is connected to the tool head through a rectangular 20×12 / 2 line. The dimensions of the rectangular 20×12 / 2 line are: tooth tip diameter Φ≥20-0.05-0.1, roughness Ra1.6, tooth root diameter Φ≥17.5-0.05-0.15, spacing ≥3.2, and tooth pitch ≥6.

[0034] The above description is only a preferred embodiment of the present invention, but does not limit the present invention to the scope of the described embodiments. Various modifications and variations can be made by those skilled in the art. Any modifications, equivalent substitutions, or improvements made using the present invention should be included within the protection scope of the present invention.

Claims

1. A method for machining slender, deep holes in shafts using a conventional lathe, characterized in that: The method includes: cutter head design, cutter shank design, cooling method, and a reasonable chip removal guide; the cutting axis length is >65. Cutting head design: The cutting head material is made of ultra-hard high-speed steel with high hardness, high wear resistance and high high temperature hardness. It is quenched at 1220~1250℃ and tempered at 550~600℃ to achieve a Rockwell hardness of 66~69. According to the diameter of the shaft-type slender deep hole machining parts, the cutting head is made with a cutting edge tip rake angle ≤10°, a cutting edge tip back helix angle ≤14°, a cutting edge rotation angle ≤30° in the direction of the cutting axis generatrix, and a chip groove cutting axis with a chip groove bottom inclination ≥20°. The cutting edge tip angle is ≤2° and the cutting core tip angle at the axial center is ≤6°. It is made into a guide chip removal cutting edge group tooth boring tool with a cutting edge helical tooth number Z≥4. The tool holder is made of high-strength tempered steel with a hardness greater than HRC35~40. The diameter of the tool holder is the cutting edge diameter minus 4~6mm. It is coaxially connected to the chip groove cutting edge. The tool holder part at the front end of the tool holder is threaded to the tool head in a rectangular shape. The tool holder end has a center hole. The center of the tool holder has an axial cooling hole that connects to the cooling hole of the chip groove cutting edge. The tool holder is connected to the lathe tailstock in a stepped shaft manner. The connecting part is cylindrical for milling flat surfaces. The working length of the flat milling surface is ≥25 times the diameter of the tool head. Cooling method: The diameter of the tool holder is adjusted within the range of Φ4~Φ7 according to the diameter of its internal cooling holes. The axial cooling holes inside the tool holder are connected to at least 4 chip groove cutting axis cooling holes inside the tool head. When machining slender holes, the slender deep hole machining parts of the shaft type are mounted on the lathe guide rail using a lathe chuck and center rest. The cooling hose is connected to the toothed thread of the axial cooling hole at the end of the tool holder section. The coolant enters the boring cooling area directly through the axial cooling hole at the center of the shaft control tool holder and the chip groove cutting axis cooling holes of the tool head for cooling. The tool holder is fixed on the lathe tool post. The boring chips are pushed by the drag of the lathe tool post and the follow post. The chip grooves of the cutting axis discharge the broken, rolled, and shattered chips in time.

2. The machining method for slender deep holes of shaft type using a conventional lathe as described in claim 1, characterized in that: The cutting head is used to machine slender holes with a diameter Φ≥34, a machining depth >500, and a length-to-diameter ratio L / D>10.

3. The machining method for slender deep holes of shaft type using a conventional lathe as described in claim 1, characterized in that: The diameter of the cutting edge is φ≥34, and the length of the cutting shaft is ≥65.

4. The machining method for slender deep holes of shaft type using a conventional lathe as described in claim 1, characterized in that: The chip groove cutting shaft has at least 4 cooling holes with a diameter of Φ≤2.

5. The cylindrical part connecting the chip groove cutting shaft and the tool shank has a diameter of Φ≥30 and a length of ≥20. The cylindrical part of the connecting part has a milling thickness of ≥27 and a length of ≥18. The tool shank is connected to the tool holder by a rectangular 20×6 line and is positioned by an outer circle with a diameter of Φ≥20.5 and a surface roughness of Ra0.8 and an outer circle with a diameter of Φ16.98~Φ16.

99.

5. The machining method for slender deep holes of shaft type using a conventional lathe as described in claim 1, characterized in that: The tool holder is made of 30CrMnSiA material with a hardness of HRC35~40. This tool holder is used in conjunction with the tool head. The working part of the tool holder has a diameter Φ≥300 and a length ≥555. The connecting part has a diameter Φ≥25 and a length ≥80. The hole dimensions for the inner diameter of the tool holder positioning are ≥Φ20.5 and ≥16, and Φ≥17 and ≥11, respectively. The diameter of the axial cooling hole at the center of the tool holder is Φ≥7.

6. The machining method for slender deep holes of shaft type using a conventional lathe as described in claim 1, characterized in that: The tool holder is connected to the chip groove cutting head via a rectangular 20×6 line. The dimensions of the rectangular 20×6 line are: tooth tip diameter Φ≥20, tooth root diameter Φ≥17.5, spacing ≥3.2, and tooth pitch ≥6.

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