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The causes and solutions of precision turning various parts' common surface defects!

A. The outer diameter taper of cylindrical workpieces exceeds the tolerance after processing

Reason for occurrence:

1. The centerline of the headstock spindle exceeds the tolerance for non parallelism of the slide moving guide rail.

2. The inclination of the bed guide rail exceeds the tolerance or deforms after assembly.

3. The bed guide surface is severely worn, and the unevenness in the horizontal plane and the inclination during the movement of the slide have exceeded the tolerance.

4. Because the centerline of the spindle taper hole and the centerline of the tailstock top taper hole are not on the same straight line.

5. The influence of cutting tools, the blade is not wear-resistant.

6. The high temperature rise of the headstock causes thermal deformation of the machine tool: the main shaft, bearings, friction clutches, gears and other transmission components in the headstock generate frictional heat due to movement, which is absorbed by the lubricating oil and becomes a large secondary heat source. The heat is transferred from the bottom of the headstock to the bed and headboard, causing the temperature of the bed joint to rise and expand, resulting in thermal deformation of the machine tool.

resolvent:

1. Re calibrate the installation position of the headstock spindle centerline to ensure that the workpiece is within the allowable error range.

2. Adjust the shim to recalibrate the inclination of the bed guide rail.

3. When the unevenness of the slide moving in the horizontal plane and the inclination of the slide moving exceed the tolerance, there are no large scratches on the guide rail surface, which can be repaired by scraping and grinding the guide rail. If the deviation is significant, the guide rail should be finely planed or ground.

4. Adjust the screws on both sides of the tailstock to eliminate taper.

5. Trim the tool, select the spindle speed and feed rate correctly.

6. When processing in cold state, the accuracy of the workpiece is qualified, but the workpiece only exceeds the tolerance after running for hours. Therefore, the oil supply of the front bearing of the spindle should be adjusted appropriately, the appropriate lubricating oil should be replaced, and the oil pump inlet should be checked for blockage.

B. Ellipses and angular circles are generated after workpiece processing

Reason for occurrence:

1. The clearance between the main shaft bearings is too large (due to the presence of many particles under mechanical wear in the lubricating oil, critical friction occurs when the shaft is subjected to heavy loads, and insufficient or blocked supply of lubricating oil can cause serious wear on the bearings).

2. The ellipse of the spindle neck is too large.

3. The main shaft bearing is worn, or the precision of the last stage gear of the main shaft exceeds the tolerance, resulting in vibration during rotation.

4. The outer diameter of the main shaft bearing sleeve is elliptical or the shaft hole of the headboard box is elliptical, or the clearance between the two is too large.

5. The tip of the machine tool needle is worn off center, or the hole of the workpiece needle is not round.

resolvent:

1. Adjust the clearance of the spindle bearings; If the lathe frequently operates at high speeds, the adjustment gap should be slightly larger. If it frequently operates at low speeds, the gap should be smaller. If the spindle clearance is adjusted at low speed, there is often a possibility of shaft hugging during high-speed operation. Therefore, the speed range should be adjusted according to the daily use specifications of the lathe, and the general clearance should be between 0.02 and 0.04 millimeters.

2. Grind the journal of the spindle to meet the requirements for roundness.

3. Scrape and grind the bearing, repair the journal, replace the rolling bearing or final gear.

4. When the out of roundness and taper of the shaft hole exceed the tolerance, it should be first scraped and straightened, and then repaired using methods such as "local nickel plating"; If it is a sliding bearing, a new bearing sleeve must be replaced.

5. Repair and grind the pin or workpiece pin hole.

C. When refining the outer surface of the car, ripples repeatedly appear at regular intervals

Reason for occurrence:

1. The longitudinal blade small gear and rack of the chute box are not meshing properly.

2. The bending of the light rod or the installation holes of the light rod, screw rod, and cutting rod are not on the same plane.

3. One of the transmission gears (or worm gears) inside the chute box is damaged, or the kneading is incorrect due to pitch oscillation.

4. The shaft in the headboard box and knife box is bent or the gear is damaged.

resolvent:

1. When the distance between the ripples is the same as the tooth pitch of the rack, it can be considered that this kind of ripple is caused by the gear rack. The meshing clearance should be adjusted and the gear rack should mesh over the full width of the tooth surface.

2. In this case, only regular periodic ripples appear repeatedly: if the light rod is bent, the light rod should be removed and straightened; During assembly, the three holes should be kept coaxial and on the same plane; There should be no light or heavy movement of the slide board.

3. Check and calibrate the transmission gears inside the carriage box, and replace them if damaged.

4. Check the transmission shaft and gears, straighten the transmission shaft, and replace damaged gears.

D. When refining the outer circle, regular ripples repeatedly appear on the circumferential surface parallel to or at a certain angle to the spindle axis

Reason for occurrence:

1. The gear teeth on the main shaft are worn or pinched poorly.

2. The clearance between the main shaft bearings is too large or too small.

3. Machine tool vibration is caused by factors such as excessive outer diameter of the pulley or belt groove vibration on the headboard box.

resolvent:

1. When such ripples appear, if the number of heads (or lines) of the ripples is the same as the number of teeth on the transmission gear on the main shaft, it can be determined that it is caused by the transmission gear on the main shaft. This situation usually occurs when the meshing clearance of the gear pair is not appropriate after adjusting the main shaft bearing. The meshing clearance should be maintained at around 0.05 millimeters; When the meshing clearance is too small, use grinding paste to grind the gears, and then disassemble and clean them all. When the meshing clearance is large or the tooth wear is severe and the ripple cannot be eliminated, the main shaft gear should be replaced.

2. Adjust the clearance between the spindle bearings. The axial runout of rolling bearings is less than 0.005 millimeters.

3. Eliminate the eccentric vibration of the pulley, adjust the clearance of its rolling bearings, and eliminate other vibration sources that cause machine tool vibration.

E. When refining the outer circle of the workpiece, there is a fixed length of corrugated protrusion on the circumferential surface of the workpiece

Reason for occurrence:

1. The bed guide rail has scratches and protrusions at a fixed length position.

2. The surface of the rack protrudes at a certain point or the joint between the racks is poor.

resolvent:

1. Repair bumps, protrusions, and other burrs.

2. Check and calibrate the joint between the two racks, adjust the protruding surface of the rack to match the tooth thickness of other single tooth surfaces.

F. When refining the outer circle of a car, there are chaotic ripples on the surface of the circumference

Reason for occurrence:

1. The raceway of the spindle rolling bearing is worn.

2. The axial clearance of the spindle is too large.

3. When using the tailstock to support workpiece cutting, the top sleeve is unstable.

4. When using a chuck to clamp the workpiece for cutting, the loose fit between the internal thread of the chuck flange hole and the centering journal thread at the front end of the spindle can cause the workpiece to become unstable, or the claw can form a horn hole shape, resulting in unstable clamping of the workpiece.

5. The square tool holder deforms due to clamping the tool, causing poor contact between its ground and the surface of the upper tool holder bottom plate.

6. The gap between the sliding surfaces of the upper and lower knife holders (including the slide) is too large.

7. The three supports of the knife box and the slide box bracket have different axes, and there is resistance (jamming phenomenon) when rotating.

resolvent:

1. Replace the rolling bearings of the spindle.

2. Adjust the clearance of the thrust ball bearing at the rear end of the spindle.

3. Check the top sleeve and shaft hole of the tailstock, as well as the clamping device. If it loses its function, repair the shaft hole first, and then match the tailstock top sleeve according to the actual size after bearing repair.

4. Change the clamping method of the workpiece and use the tailstock to support it for cutting. If the random pattern disappears, it can be determined that it is caused by the wear of the chuck flange. At this time, a new chuck flange can be configured according to the centering journal and front thread of the spindle. When the chuck has a horn hole, generally adding copper pads can solve the problem.

5. Scrape and train the joint surface of the bottom plate of the square knife holder to achieve uniform and comprehensive contact.

6. Adjust the iron clamping plates of all guide rail pairs to ensure even fit and smooth and lightweight shaking.

7. Check all supports and if necessary, remove and reassemble them.

G. When refining the outer circle of the car, there is a vibration mark on the circumferential surface of the main shaft every time it rotates

Reason for occurrence:

1. Several rollers of the main spindle rolling bearing are severely worn.

2. The pitch diameter vibration of the transmission gear on the main shaft is too large.

resolvent:

1. Replace the bearings.

2. Eliminate the pitch oscillation of the main shaft gear, and replace the gear pair if it is severe.

H. After precision machining, the workpiece end face is convex

Reason for occurrence:

1. The unevenness of the centerline of the headstock spindle caused by the movement of the slide board exceeds the tolerance.

2. The verticality of the upper and lower guide rails of the slider exceeds the tolerance.

resolvent:

1. Correct the position of the spindle centerline of the headboard box, ensuring that the workpiece cone is qualified, and then tilt the spindle centerline forward, that is, towards the tool holder.

2. Scrape and grind the guide surface of the slide board, and make the outer end of the upper guide rail of the slide board lean towards the headboard box.

I. When refining the end face, the non parallelism exceeds the tolerance

Reason for occurrence:

1. The dovetail groove surface of the upper guide rail of the slider is not straight.

2. The screw rod and nut of the middle drag plate are not concentric.

resolvent:

1. Scrape the training directly onto the guide rail surface.

2. Adjust the screw rod and nut to ensure concentricity.

J. The end face vibration after finishing the car exceeds the tolerance

Reason for occurrence:

1. The axial clearance of the spindle is too large or the axial displacement exceeds the tolerance.

resolvent:

1. Adjust the axial clearance and runout of the spindle to ensure a tolerance within 0.02 millimeters.

K. When precision machining large end workpieces, ripples repeatedly appear at regular intervals in the diameter direction

Reason for occurrence:

1. The wear of the guide rail on the slide board causes unstable phenomena such as gaps when the slide seat of the tool holder moves.

2. The horizontal screw is bent.

3. The clearance between the horizontal screw and nut is too large due to wear.

resolvent:

1. Scrape and grind together with guide rails and iron plugs to ensure stability when the tool holder slides down.

2. Straighten the horizontal screw rod.

3. Adjust the gap between the screw rod and the nut. First, loosen the screw on the left end nut, then use the middle screw to pull up the wedge iron, adjust it to the appropriate gap, and finally tighten the left nut.

L. Uneven pitch and irregular patterns during thread turning

Reason for occurrence:

1. The machine tool screw is worn and bent, and the opening and closing nut is worn and poorly engaged with the screw due to different axes. The gap is too large, and it is due to the wear of the dovetail guide rail that the opening and closing nut is unstable when closed.

2. The clearance between the transmission chain coming from the main shaft through the hanging wheel is too large.

3. The axial clearance of the screw is too large.

4. The metric and imperial handles are hung incorrectly, the fork position is incorrect, or the hanging wheel on the hanging wheel rack is hung incorrectly.

resolvent:

1. Straighten the screw rod, adjust the gap between the screw rod and the opening and closing nut pair, trim the dovetail guide rail to ensure stability when the opening and closing nut is closed.

2. Check the meshing clearance of each transmission component, and adjust any adjustable parts such as hanging wheels.

3. Adjust the axial clearance and movement of the screw rod.

4. Check whether the handle, fork, and hanging wheel are correct, and correct them if they are wrong.

M. The threaded surface of the workpiece after precision machining has ripples

Reason for occurrence:

1. Due to the wear of the machine tool guide rail, the slide plate tilts and sinks, causing the screw rod to bend and the engagement of the opening and closing nut to be poor, resulting in a single piece engagement.

2. The support hole of the bracket is worn, making the centerline of the screw rotation unstable.

3. The axial clearance of the screw is too large.

4. The hanging axle of the knife box is bent.

5. There is a gap between the drag plate and the slide plate in the square knife holder.

6. The contact surface between the square knife holder and the small knife holder bottom plate is poor.

resolvent:

1. Repair the slider with an additional compensation ring, which involves bonding a layer of guide plate with adhesive on the lower guide surface of the slider to compensate for the amount of sinking and tilting of the slider box caused by rail wear.

2. Drill holes and insert sleeves into the support holes of the bracket.

3. Adjust the axial clearance of the screw rod. It should be ensured to be within ≤ 0.01 millimeters.

4. Replace the bent shaft.

5. Adjust the clearance of the guide rail surface and plug iron, pressure plate, etc. Check each sliding surface with a 0.03mm feeler gauge, and the insertion depth should be ≤ 20mm.

6. Repair the base surface of the scraper rack and scrape the contact points at its four corners until soft.

N. After the clamping handle on the square knife holder is tightened, the handle of the small knife holder cannot rotate

Reason for occurrence:

1. The bottom of the square knife holder is uneven.

2. The contact surface between the square knife holder and the small knife holder bottom plate is poor.

3. After the knife holder is compressed, the square knife holder deforms.

resolvent:

1. Use a scraper to scrape the bottom surface of the square knife holder and maintain good contact.