15 tips for improving the skills of CNC lathe workers!

1. Cleverly obtaining trace amounts of depth and skillfully using trigonometric functions
In turning machining, it is common to process workpieces with inner and outer circles above second level accuracy. Due to various reasons such as cutting heat, friction between the workpiece and the tool, tool wear, and repeated positioning accuracy of the square tool holder, quality assurance is difficult. To solve the problem of precise micro depth, in turning processing, we use the relationship between the opposite and diagonal sides of the triangle as needed, and move the longitudinal small tool holder at an angle to accurately achieve the lateral depth value of the micro moving turning tool. This saves labor and time, ensures product quality, and improves work efficiency.
The scale value of the small tool holder on a typical C620 lathe is 0.05mm per grid. If you want to obtain a lateral depth value of 0.005mm, you can refer to the sine trigonometric function table:
Sin α＝ 0.005/0.05=0.1 α＝ 5 º 44 ′
Therefore, as long as the small knife holder is moved to 5 º 44 ′, a slight movement of the turning tool with a depth of 0.005mm in the horizontal direction can be achieved by moving the vertical carving disc on the small knife holder one grid.
2. Three examples of reverse turning technology application
Long term production practice has proven that using reverse cutting technology can achieve good results in specific turning processes. Here are some examples:
(1) Reverse cutting thread material is martensitic stainless steel parts
When machining internal and external threaded workpieces with pitches of 1.25 and 1.75mm, the value obtained is an inexhaustible value because the pitch of the lathe screw is removed by the pitch of the workpiece. If the method of lifting and retracting the nut handle to process threads is used, it often results in disorderly threads. Generally, ordinary lathes do not have a disorderly threading device, and making a set of disorderly threading devices is quite time-consuming. Therefore, when processing threads with this type of pitch, it is common to. The method used is the low-speed forward turning method, because the high-speed buckle cannot retract the tool in time, resulting in low production efficiency. In turning, it is easy to produce tool gnawing, and the surface roughness is poor. Especially in low-speed cutting of martensitic stainless steel materials such as 1Crl3 and 2Crl3, the tool gnawing phenomenon is more prominent. The "three reverse" cutting method created in machining practice, which includes reverse tool loading, reverse cutting, and opposite tool direction, can achieve good comprehensive cutting results. This method can cut threads at high speed, and the direction of tool movement is from left to right to exit the workpiece. Therefore, there is no problem of the tool not being able to retreat when cutting threads at high speed. The specific method is as follows:
When turning external threads, grind a tool similar to an internal thread turning tool (Figure 1);
When threading inside the car, grind a reverse internal thread turning tool (Figure 2).
Before processing, slightly tighten the reverse friction plate spindle to ensure the rotational speed during reverse starting.
Align the thread cutter, close the opening and closing nuts, start the forward and low-speed rotation to reach the empty tool slot, then insert the thread turning tool into the appropriate cutting depth to reverse the rotation. At this time, the turning tool moves from left to right at high speed, and after cutting several times using this method, the thread with good surface roughness and high precision can be processed.
(2) Reverse rolling
In the traditional forward turning and clockwise rolling process, iron filings and debris are easily entering between the workpiece and the rolling cutter, causing excessive force on the workpiece, resulting in disorderly patterns, crushed patterns, or ghosting.
If a new operation method of turning the lathe spindle horizontally and reversing the rolling pattern is adopted, it can effectively prevent the drawbacks generated during the following operation and achieve good comprehensive results.
(3) Reverse turning of inner and outer taper pipe threads
When turning various low precision requirements and small batch sizes of inner and outer tapered pipe threads, a new operating method of reverse cutting and reverse tool installation can be used directly without the need for a modeling device. While cutting, the tool can be continuously operated horizontally by hand (when turning outer tapered pipe threads, it moves from left to right, and the depth of the tool can be easily controlled from large diameter to small diameter). The reason is that there is pre pressure during the tool cutting process.
The scope of application of this new type of reverse operation technology in turning machining technology; It is becoming increasingly widespread and can be flexibly applied according to various specific situations.
3. New operating methods and tool innovations for drilling small holes
In turning machining, when drilling holes smaller than 0.6mm, due to the small diameter and poor rigidity of the drill bit, as well as the inability to increase the cutting speed, and the workpiece material being heat-resistant alloy and stainless steel, the cutting resistance is high. Therefore, when using mechanical transmission feed during drilling, the drill bit is prone to breaking. Below is a simple and effective tool and manual feed method.
Firstly, the original drill chuck is modified into a straight handle floating type. During operation, simply clamp the small drill bit onto the floating drill chuck to smoothly drill holes. Because the back of the drill bit is a straight handle sliding fit, it can move freely in the sleeve. When drilling small holes, gently grip the drill chuck with your hand to achieve manual micro feed, quickly drill out the small holes, ensuring quality and quantity, and extending the service life of the small drill bit. The restructured multi-purpose drill chuck can also be used for small diameter internal thread tapping, reaming, etc. (if drilling a larger hole, a limit pin can be inserted between the sleeve and the straight shank), as shown in Figure 3.
4. Anti vibration for deep hole machining
In deep hole machining, due to the small aperture and slender boring tool holder, turning the aperture Φ When the depth of the hole is around 1000mm, it is inevitable that vibration will occur. To prevent the vibration of the tool holder, the simplest and most effective method is to attach two supports (using materials such as adhesive tape) to the tool holder body, which are exactly the same size as the hole diameter. During the cutting process, due to the positioning and support function of the adhesive wood block, the tool holder is less prone to vibration and can process high-quality deep hole parts.
5. Anti breakage of small center drills
In turning machining, the drill is smaller than the one produced by Φ When drilling a 1.5mm center hole, the center drill is prone to breakage. A simple and effective method to prevent breakage is not to lock the tailstock when drilling the center hole, allowing the frictional force generated between the weight of the tailstock and the machine tool surface to drill the center hole. When the cutting resistance is too high, the tailstock will move back on its own, thus protecting the center drill.
6. Processing technology of "O" type rubber mold
When turning the "O" type rubber mold, there is often a phenomenon of misalignment between the female and male molds, and the shape of the pressed "O" type rubber ring is shown in Figure 4, resulting in a large amount of waste.
After multiple experiments, the following methods can basically be applied to produce "O" shaped molds that meet the technical requirements.
(1) Yang mold processing technology
① Refine the dimensions of each part and a 45 ° slope according to the diagram.
② Install the R shaped knife and move the small knife holder to 45 °. The knife alignment method is shown in Figure 5.
As shown in the diagram, when the R knife is in position A, it contacts the outer circle D at contact point C. Move the large drag plate a distance in the direction of arrow 1, and then move the horizontal knife holder X in the direction of arrow 2. Calculate X using the following formula:
X=(D-d)/2+(R-Rsin45 °)
=(D-d)/2+(R-0.7071R)
=(D-d)/2+0.2929R
(i.e. 2X=D-d+0.2929) Φ).
Then move the large drag plate in the direction of arrow 3 to make the R blade contact the 45 ° inclined plane, and the tool will be in the center position (i.e. the R blade is in position B).
③ Move the small tool holder model cavity R in the direction of arrow 4, with a feed depth of Φ/ 2.
Note ① When the R knife is in position B:
OC=R, OD=Rsin45 °=0.7071R
CD=OC OD=R-0.7071R=0.2929R,
② The X size can be controlled by a block gauge, while the R size can be controlled by a dial gauge for depth.
(2) Female mold processing technology
① Process the dimensions of each part according to the requirements in Figure 6 (cavity dimensions are not processed).
② Research and integrate 45 ° inclined plane and end face.
③ Install the R forming tool, move the small tool holder to 45 ° (move it once to process the male and female molds), and when the R tool is at position A ′ in Figure 6, make the tool contact the outer circle D (contact point C). Move the large drag plate in the direction of arrow 1 to move the tool away from the outer circle D. Then, move the horizontal tool holder X distance in the direction of arrow 2, and calculate X using the following formula:
X=d+(D-d)/2+CD
=D+(D-d)/2+(R-0.7071R)
=D+(D-d)/2+0.2929R
(i.e. 2X=D+d+0.2929) Φ)
Then move the large drag plate in the direction of arrow 3 to the 45 ° inclined plane where the R tool contacts, and the tool is currently in the center position (i.e. position B 'in Figure 6).
④ Move the small tool holder model cavity R in the direction of arrow 4, with a feed depth of Φ/ 2.
Note: ① DC=R, OD=Rsin45 °=0.7071R
CD=0.2929R,
② The X size can be controlled by a block gauge, while the R size can be controlled by a dial gauge for depth.
7. Anti vibration of turning thin-walled workpieces
During the turning process of thin-walled workpieces, vibration often occurs due to the poor rigidity of the workpiece; Especially when turning stainless steel and heat-resistant alloys, vibration is more prominent, the surface roughness of the workpiece is extremely poor, and the service life of the tool is shortened. Below are some of the simplest shock-absorbing methods in production.
(1) When turning the outer circle of a stainless steel hollow slender pipe workpiece, the hole can be filled with wood chips and plugged tightly. At the same time, cloth glue wood plugs can be inserted on both ends of the workpiece, and then the support claws on the tool holder can be replaced with cloth glue wood material support melons. After correcting the required arc, the turning of the stainless steel hollow slender rod can be carried out. This simple method can effectively prevent vibration and deformation of the hollow slender rod during cutting.
(2) When turning the inner holes of heat-resistant (high nickel chromium) alloy thin-walled workpieces, due to the poor rigidity of the workpiece and the slender tool holder, serious resonance phenomenon occurs during the cutting process, which easily damages the tool and generates waste. If rubber strips, sponges, and other shock-absorbing materials are wrapped around the outer circle of the workpiece, the shock-absorbing effect can be effectively achieved.
(3) When turning the outer circle of heat-resistant alloy thin-walled sleeve workpieces, due to comprehensive factors such as high cutting resistance of heat-resistant alloy, vibration and deformation are easily generated during cutting. If rubber, cotton thread and other debris are inserted into the workpiece hole, and then the two end faces are tightly clamped, it can effectively prevent vibration and workpiece deformation during cutting, and high-quality thin-walled sleeve workpieces can be processed.
8. Disc clamping tool
The shape of the disc-shaped part is a thin-walled part with double inclined planes. When turning the second process, it is necessary to ensure the shape and position tolerance requirements, and also to ensure that the workpiece does not deform during clamping and cutting. To achieve this, you can create a set of simple clamping tools by yourself. Its feature is to use the slanted surface of the workpiece processed in the previous process to position it, and then use the nuts of the outer slanted surface to tighten the disc-shaped part in this simple tool. This can be used to perform the arc R on the end face, hole opening, and outer slanted surface, as shown in Figure 7.
9. Precision boring large diameter soft claw limiting tool
In the turning and clamping of precision workpieces with larger diameters, in order to prevent the movement of the three claws due to gaps, it is necessary to pre clamp a bar material with the same diameter as the workpiece at the rear of the three claws in order to repair the boring of the soft claws. Our self-made precision boring large diameter soft claw limit tool is characterized by (see Figure 8), and the three screws of part l can be adjusted in the fixed plate as needed to support the diameter size, thereby replacing various bar materials with different diameters.
10. Simple and precise additional soft claws
In turning machining, it is common to encounter the processing of medium and small precision workpieces. Due to the complexity of the inner and outer shapes of the workpieces, as well as the strict requirements for shape and position tolerances, we have added a set of self-made precision soft claws to the three jaw chuck of lathes such as C1616 to ensure the various shape and position tolerance requirements of the workpieces. The workpieces will not be damaged or deformed during multiple clamping operations. This precision soft claw is easy to manufacture, using aluminum alloy rods to turn the end as needed, then drilling and boring holes, drilling a base hole on the outer circle and tapping M8. After milling both sides, the workpiece can be installed on the hard jaws of the original three jaw chuck. It can be locked onto the three jaws with M8 internal hexagonal screws, and then precisely bored with positioning holes as needed to clamp the workpiece in the aluminum soft jaws for cutting processing. The adoption of this achievement will generate significant economic benefits, as shown in Figure 9.
11. Additional shock-absorbing tools
Due to the poor rigidity of slender axis workpieces, vibration is prone to occur during multi slot cutting, resulting in poor surface roughness of the workpiece and damage to the tool. A self-made set of additional shock-absorbing tools can effectively solve the vibration problem of slender parts during groove cutting processing (see Figure 10).
Install the self-made additional shock-absorbing tool in a suitable position on the square knife holder before work. Then, install the required groove turning tool on the square tool holder, adjust the distance and the compression amount of the spring, and proceed with the operation. When the turning tool cuts into the workpiece, an additional shock-absorbing tool is also pressed against the surface of the workpiece, providing good shock-absorbing effect.
12. Additional movable top cap
When turning various shapes of small shafts for precision machining, it is necessary to use a convertible top tip to hold the workpiece in order to perform cutting. Due to the different shapes and small diameters of the workpiece ends, which are not suitable for ordinary live tips, I have personally manufactured various shapes of additional live tip caps in production practice, which can be installed on ordinary live tips and can be used. The structure is shown in Figure 11.
13. Application of honing precision machining for difficult to machine materials
When precision turning difficult to machine materials such as high-temperature alloys and quenched steel, the surface roughness of the workpiece is required to be between Ra0.20 and 0.05 μ m. The dimensional accuracy is also relatively high. The final finishing is usually carried out on a grinder.
Making a set of simple honing tools and honing wheels by oneself and using honing instead of precision grinding on a lathe has achieved good economic results.
Honing wheel
Manufacturing of honing wheels
① Ingredients
Adhesive: 100 grams of epoxy resin
Abrasive: Diamond sand (single crystal corundum for difficult to process high-temperature nickel chromium materials) 250-300 grams. Ra0.80 μ M uses No. 80, Ra0.20 μ M uses 120-150, Ra0.05 μ Use sizes 200-300 for m.
Hardening agent: 7-8 grams of ethylenediamine.
Plasticizer: 10-15 grams of dibutyl phthalate.
Mold material: HT15-33 shape.
② Pouring method
Release agent: Heat the epoxy resin to 70-80 ℃, add 5% polystyrene, 95% toluene solution, and dibutyl phosphobenzoate, stir well, then add diamond (or single crystal corundum) and stir well, then heat to 70-80 ℃, wait for cooling to 30-38 ℃, add ethylenediamine and quickly stir evenly (2-5 minutes), then pour it into the mold, and keep it at a temperature of 40 ℃ for 24 hours before starting the mold.
③ Linear speed V=V1COS α (V is the relative speed of the workpiece, that is, the grinding speed under the condition of no longitudinal feed of the honing wheel), which generates a grinding effect on the workpiece. During honing, in addition to rotation, the workpiece axis is also subjected to complex motion with the feed rate S.
V1=80-120m/min
T=0.05~0.10mm
Margin<0.1mm
④ Cooling: Mix 70% kerosene with 30% No. 20 engine oil, and correct the honing wheel (pre honing) before honing.
The structure of the honing tool is shown in Figure 13.
14. Quick loading and unloading spindle
In turning machining, various types of bearing kits are often encountered for precision turning of outer circles and inverted guide cone angles. Due to the large batch size, loading and unloading during the machining process, tool change assistance time is longer than cutting time, and production efficiency is low. The quick loading and unloading spindle and single tool multi blade (hard alloy) turning tool introduced below can save auxiliary time and ensure product quality in processing various bearing sleeve parts. The production method is as follows.
To make a simple small taper spindle, the principle is to use a slight taper of 0.02mm at the back of the spindle. After the bearing is assembled, the parts are tightened onto the spindle by friction, and then a single blade multi blade turning tool is used. After turning the outer circle, a 15 ° taper angle is chamfered, and the workpiece is pulled out quickly and well with a handle, as shown in Figure 14.
15. Turning of Quenched Steel Parts
(1) One of the key examples of turning quenched steel parts
① High speed steel W18Cr4V quenched and drawn

① Reconstruction and regeneration of high-speed steel W18Cr4V quenched and hardened broach (repair after fracture)
② Self made non-standard thread plug gauge (hardened hardware)
③ Turning of Quenched Hardware and Sprayed Parts
④ Turning of hardened hardware smooth plug gauge
⑤ Thread pressure tap modified with high-speed steel cutting tools
For the quenching hardware and various difficult to machine material parts encountered in the above production, selecting appropriate tool materials, cutting amounts, tool geometric angles, and operating methods can achieve good comprehensive economic results. If the square mouth broach is regenerated after fracture, and if a square mouth broach is produced again, not only will the manufacturing cycle be long, but also the cost will be high. We will use hard alloy YM052 and other blade edges to grind to a negative front angle r at the root of the original broach fracture=- 6 °~-8 °, the cutting edge can be carefully ground with an oilstone before turning, with a cutting speed of V=10-15m/min. After turning the outer circle, cut the empty tool groove, and finally turn the thread (divided into coarse and fine turning). After rough turning, the tool must be ground and polished from a new edge before finishing the outer thread. Then, prepare an inner thread connecting the pull rod, and then adjust it after connecting. A broken and scrapped square mouth broach has been turned and repaired, remaining as old as new.
(2) Selection of Tool Materials for Turning Hardening Hardware
① New grades of hard alloy blades such as YM052, YM053, YT05, etc. generally have cutting speeds below 18m/min, and the surface roughness of the workpiece can reach Ra1.6-0.80 μ M.
② The cubic boron nitride cutting tool FD can process various quenched steels and sprayed parts, with a cutting speed of up to 100m/min and a surface roughness of Ra0.80-0.20 μ M. The composite cubic boron nitride cutting tool DCS F produced by the state-owned Capital Machinery Factory and Guizhou Sixth Grinding Wheel Factory also has this kind of performance. The processing effect is better than that of hard alloy (but the strength is not as good as hard alloy, the depth of penetration is small, and the price is more expensive than hard alloy. In addition, if used improperly, the cutting head is easily damaged).
⑨ Ceramic cutting tools have a cutting speed of 40-60m/min and poor strength.
The above types of cutting tools have their own characteristics in turning quenched parts, and should be selected based on specific conditions such as different materials and hardness during turning.
(3) Selection of Types of Quenched Steel Parts with Different Materials and Tool Properties
Quenched steel parts made of different materials have completely different requirements for tool performance under the same hardness, which can be divided into three categories:;
① High alloy steel: refers to tool steel and mold steel (mainly various high-speed steels) with a total alloying element content exceeding 10%.
② Alloy steel: refers to tool steel and mold steel with an alloy element content of 2-9%, such as 9SiCr, CrWMn, and high-strength alloy structural steel.
③ Carbon steel: includes various carbon tool steels and carburized steels such as T8, T10, 15 # steel or carburized steel of 20 # steel.
For carbon steel, the microstructure after quenching is tempered martensite and a small amount of carbides, with a hardness range of HV800-1000, which is much lower than the hardness of WC and TiC in hard alloys and A12D3 in ceramic cutting tools. In addition, it has lower thermal hardening than martensite without alloying elements, generally not exceeding 200 ℃. With the increase of alloy element content in steel, the carbide content in steel after quenching and tempering also increases, and the types of carbides become quite complex. Taking high-speed steel as an example, the content of carbides in the microstructure after quenching and tempering can reach 10-15% (volume ratio), and it contains types of carbides such as MC, M2C, M6, M3, 2C, etc. Among them, VC has a high hardness (HV2800), which is much higher than the hardness of hard point phases in general tool materials. In addition, due to the presence of a large number of alloy elements, the thermal hardening of martensite containing multiple alloy elements can be increased to around 600 ℃. Therefore, the machinability of quenched steel with the same macroscopic hardness is not the same, and the difference is significant. Before turning quenched steel parts, analyze which type they belong to, master their characteristics, select appropriate tool materials, cutting amounts, and tool geometric angles, and the machinability can be improved. Successfully completed the turning process of hardened steel parts.