Analysis of Common Problems in the Use of Ordinary Lathes

As the most widely used basic equipment in the field of mechanical processing, the ordinary lathe undertakes the processing tasks of various rotary parts and plays an irreplaceable role in medium and small batch production and maintenance processing. However, during long-term use, due to factors such as component wear, improper operation, and lack of maintenance, ordinary lathes may encounter various malfunction problems, which not only affect processing accuracy and production efficiency, but in severe cases, may also cause safety accidents. Sorting out the common problems encountered during the use of ordinary lathes and analyzing their causes can help operators identify faults in a timely manner, carry out repairs quickly, and ensure the stable operation of the equipment.

Ⅰ. Common Problems of the Spindle System

The spindle system is the core moving part of a common lathe, bearing the main load of cutting processing and also a high-risk area for faults. Common problems mainly focus on four aspects:

1. Spindle speed change and gear position failure

The most common problem is that it is difficult to move the spindle speed change handle and the speed change cannot be completed. This kind of problem is mostly due to the loosening of the positioning screw in the headstock box, causing the positioning plate to shift and the handle to be stuck and unable to move normally. The second issue is that the low-speed gear of the main shaft drops, automatically returning to the empty position during processing. The main reason is that the eccentric shaft nut of the main shaft slider is loose, causing displacement after long-term force and vibration, which leads to the failure of the gear lock. In addition, some lathes may also encounter the problem of slow spindle start-up. The main reason is that the clearance of the I-axis friction clutch is too large, resulting in insufficient power transmission and the inability to quickly drive the spindle to reach the rated speed.

2. Abnormal heating and noise of the main shaft

If the main shaft rotates at high speed for a long time and the temperature abnormally rises, it is mostly because the bearing clearance of the main shaft is too small, increasing the friction force and generating a large amount of heat accumulation, or the lubricating oil passage is blocked, resulting in insufficient lubrication and intensified friction. Severe spindle heating can cause thermal deformation, resulting in unequal heights between the spindle and the tailstock center. This directly affects the machining accuracy of the workpiece and may even burn out the bearings and the spindle.

Noise is a typical precursor to a malfunction. If the headstock of the lathe makes a rumbling sound as soon as it is started, it is very likely that the bearing of the I-axis is damaged. If the noise is too loud when the main shaft is running and disappears after idling, it is usually because the main shaft bearing is worn or damaged and needs to be replaced in time. In addition, gear wear and poor lubrication can also lead to increased noise, and the noise will become more obvious as the temperature rises and the load increases.

3. The spindle accuracy is inaccurate

Excessive radial swing or axial movement of the main shaft will directly lead to unqualified dimensional accuracy of the processed workpiece and the appearance of ripples on the surface. This kind of problem is mostly due to long-term wear of the main shaft bearing, increasing the clearance, or wear of the main shaft taper hole, which cannot firmly clamp the tool or workpiece. It is necessary to adjust the bearing clearance. When the wear is severe, the bearing should be replaced and the taper hole accuracy should be repaired.

Ⅱ. Common Problems of Feed Tool Rest System

The feed system is responsible for driving the tool rest to complete linear feed motion, which directly affects the dimensional accuracy and surface quality of the workpiece. Common problems include:

1. Automatic feed failure

If the automatic feed cannot be achieved during the processing, the first step is to check whether the operation is correct: for a regular lathe, feed only occurs when the feed handle is pulled to the right, while pulling it to the left usually results in an empty position. If the operation direction is incorrect, it will directly lead to the failure of feed. After ruling out operational issues, it is necessary to inspect the hanging wheel frame. If the nut of the hanging wheel frame is loose, it will cause the hanging wheel to come apart, preventing power transmission. The position of the hanging wheel needs to be readjusted and the nut of the hanging wheel frame tightened. In addition, the automatic feed handle of the slide box is prone to disengagement. This is mostly due to insufficient spring pressure of the fallen worm or a change in the inclination Angle between the control board and the lever. It is necessary to adjust the spring pressure and repair the worn control board by welding.

2. Fault of rapid movement of the slide plate

After pressing the quick button, the slide plate cannot move. It is most likely that the quick button SB5 has poor contact, and the electrical contact failure causes the power to fail to be connected. Simply replace the button to eliminate the fault. If it still cannot be moved after adjustment, it is necessary to check the power supply line and transmission mechanism of the fast motor to check whether the motor is damaged and whether the transmission gears are stuck.

3. Vibration issues during grooving processing

Vibration of the cutting tool during slotting is a very common problem, which can lead to a rough surface of the groove. In severe cases, it may even cause the tool to break, resulting in safety accidents. There are many reasons for vibration: First, the tool Angle is unreasonable, with the rake Angle and relief Angle being too large, resulting in insufficient tool rigidity; The second is the improper selection of tool material, which does not match the material of the workpiece being processed. The third reason is that the main shaft bearing is loose, and the excessive clearance causes the main shaft to shake. The fourth reason is that the strength of the tool holder is insufficient or the cantilever extends too long, resulting in insufficient rigidity and causing vibration. The fifth issue is that the clearance between the middle drag plate and the lower slide plate is too large, resulting in insufficient contact rigidity.

Ⅲ. Common Problems of Machining Accuracy Deviation

The most common quality issue during use is that the precision of workpieces processed by ordinary lathes does not meet the requirements. Common types of deviations and their causes include:

1. The external conicity is out of tolerance

After turning the outer circle, if the taper of the workpiece exceeds the tolerance, the vast majority of the reasons are that the installation level accuracy of the machine tool exceeds the standard, and the longitudinal or transverse level deviation of the bed guide rail is too large. The installation requirements for ordinary lathes stipulate that the longitudinal horizontal accuracy should not exceed 0.02/1000mm and the transverse accuracy should not exceed 0.04/1000mm. If the deviation exceeds the limit, a level should be used to measure again, adjust the wedge-shaped shims, correct the horizontal accuracy, and then tighten the anchor bolts.

2. The surface quality of the processed part is substandard

After processing, the surface of the workpiece is rough and has irregular patterns. Besides tool wear and unreasonable cutting parameters, it may also be caused by excessive clearance of the machine tool guide rails, movement and shaking of the slide plate, or excessive clearance of the lead screw nut of the middle slide plate, resulting in uneven feed. In addition, the vibration of the main shaft can also cause regular ripples on the surface of the workpiece. It is necessary to check the clearance of the main shaft bearing and adjust and tighten it in time.

3. Workpiece deformation and tool fracture

Deformation of workpieces after processing is mostly due to improper clamping. If the workpiece is clamped too tightly, it will undergo elastic deformation, or if it is clamped too loosely, it will shift during processing. For slender shafts and thin-walled parts, if reasonable auxiliary supports are not adopted, it can also cause processing deformation. The main reasons for tool breakage are improper selection of tool material, excessive cutting parameters, and unstable tool clamping, which require targeted adjustments.

Ⅳ. Common Issues with Electrical and Starting Systems

Electrical system faults of ordinary lathes are also quite common. The most prominent one is that the main motor cannot start. Such problems can be investigated step by step: First, check if the circuit breaker is open. If it trips, it needs to be re-closed. Secondly, check whether the protective door of the belt cover is closed properly. If the belt cover door is not closed, it will trigger the travel switch SQ1 to open, and the machine cannot be started. Just close the door and connect the travel switch. Finally, check if the stop button has been reset. If the stop button is stuck and not reset, you need to unscrew it in the direction of the arrow to reset it. In addition, a blown fuse, a damaged control transformer, or a damaged contactor can also prevent the motor from starting. It is necessary to check and replace each damaged component one by one.

Ⅴ. Analysis of Common Causes of the Problem

A review of various common problems with ordinary lathes reveals that the causes of faults can be classified into four major categories: First, natural wear of components. After long-term use of the lathe, moving parts such as bearings, gears, guide rails, and lead screws will inevitably wear out, gradually reducing precision and eventually leading to faults. Second, the installation and assembly accuracy is insufficient. During the installation of the lathe, the horizontal accuracy correction is not in place, and the precision control during the assembly of the spindle box, feed box, and slide box is not strict. This will plant potential faults from the initial stage of use. Thirdly, the operation and use are not standardized. Operators do not follow the operating procedures, use the lathe beyond the processing range, and run it under overload for a long time, which will accelerate the wear of components and cause various faults. Fourth, maintenance and upkeep were inadequate. Daily cleaning and lubrication were not carried out properly, and the clearances of components were not adjusted regularly. As a result, the lathe operated with faults for a long time, and minor malfunctions gradually evolved into major problems.

The malfunction problems of ordinary lathes may seem complex, but in fact, the vast majority of them accumulate gradually during the usage process. As long as daily maintenance and care are done well, operation is standardized, and accuracy is checked regularly, the occurrence rate of malfunctions can be effectively reduced. When a malfunction occurs, it should be gradually investigated based on the fault symptoms. Once the cause is accurately identified, it can be quickly eliminated to restore the normal operation of the lathe, ensuring processing quality and production safety.