"Turner is afraid of car poles." This sentence reflects the difficulty of turning slender rods. Due to the characteristics and technical requirements of slender shaft, defects such as vibration, multi-edge, slub, poor cylindricity and bending are easy to occur in high-speed turning. If we want to make it better, we must pay full attention to the problems in the process.

1) machine tool adjustment

The connecting line between the lathe spindle and tailstock center line and the lathe guide rail must be parallel up and down, left and right, and the tolerance should be less than 0.02 mm.

2) Workpiece installation

When installing, try not to over-position. When clamping one end with chuck, do not exceed10mm. ..

3) Cutting tools

When using the offset cutter with κ R = 75 ~ 90, pay attention to the small rake angle α′ 0 ≤ 4 ~ 6, and never be larger. When installing the tool, it should be slightly higher than the center.

4) After installation, the tool rest must be trimmed.

The dressing method can be grinding, reaming, boring and other methods, so that the cambered surface R in contact with the tool holder is not less than the radius of the workpiece, and not less than the radius of the workpiece, so as to prevent polygon. When adjusting with the tool holder claw, just make the claw contact with the workpiece, and don't use force to prevent slub.

5) Auxiliary support

When the length-diameter ratio of the workpiece is greater than 40, auxiliary support should be added in the turning process to prevent the workpiece from vibrating or bending due to centrifugal force. Pay attention to the adjustment of the top when cutting, it is advisable to just top the workpiece, but it doesn't matter, and adjust it at any time to prevent the workpiece from thermal expansion, deformation and bending.

2. Reverse feed turning slender rod

There are many ways to turn slender rods, and generally the tool rest is used for forward or reverse rotation. However, compared with forward turning, reverse turning has many advantages, so it is widely used.

There are two problems in turning, one is polygon, which is mainly caused by the large rake angle of the tool, which is inconsistent with the tool holder claw R and the diameter of the workpiece; The other is the slub problem, which is that the cutting depth suddenly increases from the minimum to the cutting surface after the frame mouth follows the tool rest, which changes the cutting force, and the workpiece evades outward and the diameter suddenly increases. When the tool holder is followed to a larger diameter, the diameter of the lathe becomes smaller, and so on, so that the machined workpiece is bamboo-shaped.

In order to prevent the appearance of slub, when turning the frame mouth, carefully follow the tool rest, align it before turning the tool, use the handle of the middle carriage, and then eat (0.04 ~ 0.08) mm deep, but grasp it flexibly according to the cutting depth.

3. Rolling straightening method

In machining, rolling is often used to improve the surface hardness, fatigue strength and wear resistance of workpiece, reduce the surface roughness of workpiece and prolong the service life of workpiece. At the same time, the plastic deformation of metal under the action of external force can also be used to change the internal stress to straighten shaft and rod workpieces with good rigidity.

In the process of rolling the workpiece, the rolled workpiece is bent due to uneven hardness of the surface layer under the action of external force. The bending rotation center position is high, which bears large rolling pressure and produces large plastic deformation, which makes the workpiece bend more. This phenomenon is particularly prominent when using rigid rolling tools.

The method of rolling straightening is to check the radial runout of the workpiece after the first rolling, mark the groove, adjust the groove of the workpiece to the height of the rotary center of the machine tool with a four-jaw chuck, which is in direct proportion to the bending size of the workpiece, then roll the workpiece for the second time, then correct the workpiece with a dial indicator and adjust the claws of the four-jaw chuck. Check the bending with a dial indicator. If it is still bent, adjust the workpiece with the above method and roll it for the third time until it reaches the required straightness of the workpiece. The feed length after the second time depends on the specific situation, and it is not necessary to go all the way to the end, but to use reverse feed.

Rolling straightening is generally completed in the process of rolling the workpiece, which not only does not damage the surface of the workpiece, but also makes the outer surface of the workpiece roll evenly without dead bending and is convenient to operate.

4. Screw extrusion straightening method

For large diameter, long length and multi-bend screw, extrusion straightening is adopted, and the effect is very good.

1) working principle

Using the straightening tool, under the action of external force, the bottom surface of the screw tooth is squeezed, so that its surface is plastically deformed and extends axially, changing the internal stress state of the screw and straightening it.

2) Straightening method

First, measure the bending position and direction of the lead screw on a lathe or platform, then contact the bent upper concave and lower convex with the metal backing plate, and knock the tooth bottom of the lead screw with a flat shovel and a hammer to deform the small-diameter metal of the lead screw, thus achieving the purpose of straightening. In the whole straightening process, the bending condition is detected, and the flat shovel alternately hits and squeezes until the lead screw is straightened. This method is simple and easy to operate, which is not only suitable for straightening large and small lead screws, but also suitable for straightening shaft blanks, and it is not easy to recover after straightening.

3) Problems that should be paid attention to

The dimension r of the special leveling shovel for straightening should be more than half the diameter of the screw tooth bottom, b less than the tooth bottom width, and α less than the tooth profile angle; The r section in contact with the workpiece should be rounded; After correction, the squeezed tooth base should be filed flat with a file.

5. Processing of rubber thread

Because the hardness of rubber is very low, the elastic modulus is only 2.35N, which is equivalent to 1/85000 of carbon steel. Under the action of external force, rubber is easy to deform and difficult to cut. Especially, it is more difficult to cut some special-shaped threads.

In order to solve the processing of rubber thread, a grinding head with adjustable helix angle can be installed on the lathe, or a pneumatic grinding head can be used instead when the thread accuracy is not high. The grinding wheel is a white corundum grinding wheel with a diameter of 60 mm ~ 80 mm and a particle size of 60 # ~ 100 #. After the grinding wheel is installed, the shape of the grinding wheel is trimmed with a diamond pen, and the shape of the grinding wheel is the normal cross-sectional shape of the thread.

The thread lead is small, and the lathe nameplate has it. You can get it by pulling the lathe handle directly. When there is no nameplate on the lathe, the required change gear must be calculated. Generally, you can consult the manual and find and manufacture the required change gear through calculation.

Generally, when the thread lead is greater than 300mm, the spindle speed must be reduced, so as not to affect the thread grinding quality due to the high spindle speed, and also to make the operation tense or damage the feed box parts. The methods of deceleration include: changing the diameters of driving pulley and driven pulley; Add a reducer outside the lathe.

The method of splitting is the same as the method of turning to multithreading.

Grinding rubber thread on lathe is a high-efficiency and high-quality processing technology. Single-end and multi-end rubber threads with lead of (1.5 ~ 1280) mm have been machined by grinding method, and the quality meets the requirements.

6. Step deep hole turning method

When turning a hole with a length-diameter ratio greater than 4 on a lathe, due to the poor rigidity of the tool holder, the vibration during cutting is great and turning is difficult, which affects the cutting efficiency and the quality of the machined surface. Especially in the case of large aperture, deep hole and step, it is more difficult to process because of the influence of the rigidity of tool rest and machine tool.

Firstly, the workpiece is installed on a lathe with a chuck and a center frame, and the short holes at both ends of the workpiece are machined with inner hole cutters, each of which is equipped with a sleeve and a special tool holder. When turning a long hole in the middle, firstly, insert the left support sleeve into the workpiece hole, then install the workpiece on the lathe, adjust the protruding length of the cutter head on the cutter bar, put it into the inner hole of the workpiece together with the left support sleeve, adjust the height of the cutter bar with a cutter pad, and fix the cutter bar on the square table of the lathe, so that the cutter bar can slide freely in the sleeve, and then the workpiece can rotate and start cutting until the longitudinal depth of the workpiece.

After the workpiece is processed, move the big carriage in the opposite direction, and then exit the workpiece together with the support sleeve and the cutter bar at the right end, thus unloading the workpiece. When machining the second piece, first install the left support sleeve and clamp the workpiece, then insert the cutter bar into the left support sleeve and install the right support sleeve, and then turn the second piece.

Features of the tool: the handle is supported by supporting sleeves at both ends, which greatly increases the rigidity of the handle, makes the cutting vibration free and ensures the roughness of the machined surface; Both ends are supported by supporting sleeves to rotate the cutter bar, which ensures the position accuracy between holes; The operation is simple, and the efficiency is more than 5 times higher than that of the traditional reaming method.

7. Methods of adjusting the central frame

When turning the inner hole and end face of hollow workpiece with large length and diameter, it is necessary to use the center frame. If the center frame is not properly adjusted, and the axis of the workpiece does not coincide with the axis of the machine tool spindle, there will be taper errors of end face depression, protrusion and hole during machining. In severe cases, the workpiece falls off from the chuck, resulting in an accident.

When installing this kind of workpiece, one end of the workpiece adopts a three-jaw chuck or a four-jaw chuck, and the other end is placed on the center frame. Then, put a board in the hole of the workpiece or stick a piece of paper on the end face of the workpiece with butter, lean the tip of the tailstock tip against the board or paper, select a lower spindle speed, and let the workpiece rotate for a week or two. At this point, draw a circle from the center of the circle on the board or paper, and then adjust the three supports of the center frame to align the center with the tip of the center, so that the center line of the workpiece basically coincides with the axis of the machine tool spindle. After semi-finishing, if the flatness and cylindricity of the end face are out of tolerance, it can be eliminated by slightly adjusting the three supports of the center frame.

8. Put the center drill tip into the hole skillfully.

When drilling the center hole, the center drill often breaks in the center hole and is difficult to take out because the center of lathe tailstock is inconsistent with the center of workpiece rotation, or because of excessive force, large plasticity of workpiece material and chip blockage.

If the central hole is enlarged, the original size of the central hole will be changed and the quality requirements will not be met. At this time, just use a sharpened steel wire to insert the tip into the chip holding groove of the drill tip in the central hole, move the drill tip several times, and then take out the broken central drill tip in the central hole with a magnet or a magnetic table clamp.

9. The method of eliminating defects when turning slender shaft

1) belly shape

That is, after turning, the diameter of both ends of the workpiece is small and the middle diameter is large. The reasons for this defect are the poor rigidity of the slender shaft, the unstable contact between the supporting claw of the heel rest and the surface of the workpiece, and the gap caused by wear. When turning to the middle, due to the radial force, the turning tool presses the rotation center of the workpiece to the right of the rotation center of the spindle, which reduces the cutting depth, while the rigidity of both ends of the workpiece is good and the cutting depth is basically unchanged. Due to the "give way to the knife" in the middle, the slender shaft is bulging.

Elimination method: When following the tool holder claw, pay attention to make the claw surface contact with the workpiece surface, and there can be no gap. The main deflection angle of turning tool should be 75 ~ 90 to reduce the radial force. Cast iron with good wear resistance should be used for heel tool holder claws.

2) Bamboo shape

Shaped like a bamboo joint, its pitch is about equal to the distance between the heel support claw and the turning tool tip, which appears periodically. The reason for this defect is that the gap between the big carriage and the middle carriage of the lathe is too large, and the blank material produces centrifugal force when it bends and rotates. When the tool is connected with the tool rest support reference, it produces "yielding tool", which makes the diameter of the turning section slightly larger than the reference section, and continues cutting. The tool rest support claw contacts with the larger diameter part of the workpiece, so that the rotation center of the workpiece is pressed to the turning tool side, and the diameter of the turned workpiece is reduced. In this way, the tool rest is supported on workpieces with different diameters in turn, so that the workpieces can leave and approach the lathe tool to form a regular bamboo-like shape. In addition, following the tool rest claw in the feed, the force is too large, so that the rotation center of the workpiece is pressed against the lathe tool side, which leads to the lathe diameter becoming smaller, the feed continues, and so on, and a slub is also formed.

Elimination method: adjust the clearance of each part of the machine tool to enhance the rigidity of the machine tool. When following the tool holder claw, make sure that the claw surface is firmly in contact with the workpiece, and don't use too much force. Cut more depth (0.05 ~ 0. 1) mm at the tool joint to eliminate the phenomenon of "giving way to the tool" during cutting. The cutting depth should be flexibly controlled by the rules of the machine tool.

10. Reverse knurling

In the traditional forward knurling process, chips easily enter between the workpiece and the knurling, resulting in excessive stress on the workpiece, random warping of the pattern and ghosting. If the spindle is reversed, the above shortcomings can be effectively prevented and clear patterns can be rolled.

1 1. Methods to prevent the center drill from breaking

When drilling a center hole with a diameter less than 1.5mm on a lathe, the center drill is easy to break. In addition to carefully and diligently removing chips when drilling, do not lock the tailstock when drilling, and let the tailstock self-weight and the friction of the machine tool guide rail drill. When the drilling resistance is too large, the tailstock will retreat by itself, thus protecting the center drill.

12. Turning the sleeve of small eccentric workpiece

The clamping efficiency of clamping the eccentricity of workpiece lathe with sleeve is 6 ~ 8 times higher than that with four-jaw chuck. Knowing eccentricity e and workpiece excircle diameter φ 2, the inner diameters φ 1, φ 1 = 2e+φ 2 can be obtained. When machining the inner diameter φ 1 of the fixture sleeve, we must pay attention to the accuracy of the inner hole so as not to affect the dimensional accuracy of the eccentric workpiece.

13. Spinning method

Screw conveyor mechanism is widely used in factories conveying granular materials. When the spiral shaft in this mechanism is manufactured, its spiral blades are welded with steel plates. This spiral plate has high tooth profile and small bottom diameter, and its outer diameter must be coaxial with the journal. In order to meet this requirement, the outer diameter of the spiral shaft must be machined by lathe.

This kind of shaft is generally longer. When machining the outer diameter, due to large pitch, deep teeth, thin teeth, poor rigidity and intermittent cutting, the cutting impact makes the teeth vibrate, which can not cut normally and damages the tool. In order to solve this problem, we have to reduce the cutting speed, cutting depth and feed, which greatly reduces the work efficiency.

In order to improve work efficiency and quality, a simple thread turning method is adopted, and a change gear is hung according to the pitch of the screw shaft, and a large screw is used to drive the large carriage to rotate. After turning the first knife, remember the scale of the middle drag plate. After the big carriage returns, use the small carriage to move forward (0.5 ~ 0.7) mm, and then start to take the second knife until it turns to the excircle.

The tip of the spiral shaft turned by this method is smooth, and intermittent cutting is basically eliminated, and the machining efficiency is increased by nearly 10 times compared with the original one.

14. Thread processing outside the nameplate of lathe

In many mechanical drives, the pitch and lead of multi-head worm, multi-head screw, multi-head spiral spline, variable lead worm, double lead variable tooth thickness worm and helical gear meshing worm can not be found on the nameplate of lathe, which brings difficulties to machining. This paper introduces a solution that the required pitch (or lead) cannot be found on the nameplate of lathe, which can save the trouble of changing gears.

For example, the normal module of worm meshing with helical gear on imported milling machine is 3. 175, and the circumferential modulus is 3. 184. 3. The modulus of184 can't be found on the lathe. If you want to process it, you need to calculate and make a change gear. After calculation and analysis, the modulus pitch is converted into metric pitch, that is, 3.184× 3.1416 =10.003 mm, so it can be processed according to the pitch of10 mm.

In the overhaul and maintenance of equipment, the pitch of thread is mostly measured by metric system, which will lead to nonstandard pitch. In fact, threads can be divided into ordinary threads, English threads, modular threads, pitch threads and non-standard threads, and their pitches can be converted to each other. Such as 9.4248mm, 12.5664mm, 12.7mm, 25.4mm, 7.9756mm, etc. , can be processed according to other kinds of threads, and the results are P=9.4248mm, P= 12.5664mm, which are modulus 3 and modulus 4 respectively.

Another example is 12.7mm and 25.4mm, which are English threads with 2 teeth/inch and 1 tooth/inch respectively. P=7.9756mm is a radial pitch thread with DP= 10.

15. Tooling for boring large and long inner tapered holes

When machining an inner taper hole with large diameter and long length on a lathe, if the general turning method is adopted, the vibration will be great when turning due to the poor rigidity of the tool holder, and the cutting amount will be very small, or even impossible to cut. Many times, large inner holes or inner tapered holes that meet the requirements have been successfully processed.

During machining, one end of the workpiece is clamped by the chuck and the other end is supported by the center frame. Put a countersunk hole in the spindle hole of the lathe, position one end of the cutter bar with a steel ball, and fix the cutter bar on the tailstock sleeve of the lathe with a connecting sleeve and fastening screws at the other end, so that the cutter bar does not rotate when the workpiece rotates. Because of the key, the cutter head can only slide axially on the cutter bar. One end of the wire is fixed on the cutter head, and the other end is fixed on the big carriage of the lathe. When the big carriage moves longitudinally, the cutter head is pulled to move axially to complete the feeding movement and cut.

Before installing the arbor, the lathe tailstock must be placed in front of the big carriage, so that the big carriage can pull the steel wire to drive the cutter head to move. Feed can be obtained by adjusting the handle of the feed box. When machining a tapered hole, the tailstock can be offset, so that the axis of the cutter bar and the axis of the workpiece are offset by an oblique angle in the horizontal direction. When the cutter head returns, just push the cutter head by hand.

This kind of tool is very convenient for machining large internal holes on lathe, and has simple structure and good handle rigidity.