Most problems in lathe machining occur when turning external circles and threading. , Below, we’ll introduce them one by one:

2.1 Common Problems and Solutions When Turning External Cylindrical Surfaces

    (l) Ripples appear.

Vibration caused by motor rotation, roundness errors or looseness in the main and rear bearings, poor meshing of the spindle gears, non-solid workpieces or workpieces that are excessively long and protruding, as well as loose tool holders and dull cutting edges—these factors can all lead to the appearance of chatter marks. Solutions include: avoiding vibrations induced by motor rotation; adjusting the tightness of the front and rear bearings to eliminate radial runout; promptly replacing gears with poor meshing; ensuring that workpieces are securely mounted and that hollow workpieces do not extend too far beyond the chuck; making sure the tool holder is properly locked and that its base contact surface is clean and free of metal chips; keeping the length of the cutting tool extended within a reasonable range and ensuring that the cutting edge remains sharp.

(2) When turning workpieces, if the diameter fluctuates—sometimes large, sometimes small—it may be due to looseness in the workpiece clamping mechanism, prolonged use of the cutting tool resulting in dull or worn cutting edges (even chipping), or improper tightness—or wear—of the tailstock center or support jaws. Any of these factors can cause irregularities in the turned workpiece, leading to fluctuations in its diameter.

Solution: Before turning, check that the workpiece is securely clamped; ensure that the cutting tool’s blade is sharp enough; promptly replace worn-out lathe centers and adjust their tightness to the optimal level; properly lubricate and cool the support jaws, and adjust their tightness appropriately to minimize wear.

(3) The workpiece surface is rough and has poor surface finish.

Surface roughness on workpieces is generally caused by dull or damaged cutting edges of the turning tool. Therefore, before starting turning operations, it’s essential to ensure that the tool angles are appropriate and the cutting edges are sharp enough.

2.2 Common Problems and Solutions When Turning Threads

(l) Knife jamming

The height at which the cutting tool is mounted is inappropriate; when clamping the workpiece or the cutting tool, both are not securely fastened; the cutting tool is severely worn, even showing chipped edges; or failing to select an appropriate cutting method and feed rate can all lead to tool jamming. Solutions: When mounting the cutting tool, try your best to align the tailstock center with the tool, or ensure that the tool tip is at the same height as the workpiece’s axis; make sure both the workpiece and the tool are firmly clamped—when necessary, use auxiliary tools such as the tailstock center; ensure that the cutting tool’s blade is sharp enough; whenever possible, use a flexible tool holder and adopt either left-right cutting or oblique-feed methods when machining workpieces with large pitch threads.

(2) Randomly fastening

When the leadscrew rotates one full turn, if the workpiece has not yet completed an integer number of turns, cross-threading will occur. To resolve this issue: If the thread pitch of the lathe leadscrew is an integer multiple of the workpiece’s thread pitch, while the workpiece and leadscrew are rotating together, lift the opening-closing nut, wait until the leadscrew has completed one full turn, then close the opening-closing nut again, and repeat this process. If the ratio between the leadscrew pitch and the workpiece pitch is not an integer multiple, use the forward-and-reverse cutting method to retract the tool. Specifically, after completing the first cutting pass, do not immediately lift the opening-closing nut; instead, retract the tool radially, reverse the spindle to move the cutting tool longitudinally backward, and then lift the opening-closing nut to begin the second cutting pass. Repeat this procedure. By adopting the methods described above, you can effectively prevent cross-threading from occurring.

(3) Incorrect pitch

Improper gear ratio matching or incorrect positioning of the feed box handle can result in inaccurate threads across the entire length. If the lead screw itself has excessive local pitch errors, the corresponding thread sections will also be inaccurate. Axial play in the lead screw and spindle, poor engagement between the apron’s opening/closing nut and the lead screw, unstable closing of the opening/closing nut, and excessive backlash in the gear train can all cause uneven pitch along the entire length of the thread. Solutions: Ensure that the feed box handle is correctly positioned or verify and adjust the gear ratios to ensure proper matching; maintain the accuracy of the lead screw and promptly replace or adjust any lead screws that fail to meet specifications; adjust all nuts to minimize axial clearances and axial play; and keep the gear train backlash as small as possible. (Occasional spiral patterns may appear. The gear transmission between the spindle and the lead screw exhibits periodic errors, which cause the lead screw’s rotation to become periodically uneven. This, in turn, leads to periodic irregularities in the tool’s movement, resulting in the formation of spiral patterns.)

Solution Repair or replace gears that are inaccurate or worn in a timely manner.

(5) The mean diameter is incorrect.

Due to excessive cutting depth and an inaccurate dial indicator, coupled with the operator’s failure to perform timely and careful measurements, the median diameter turned out to be incorrect. Solution: Carefully check whether the dial indicator is accurate; leave an appropriate amount of finishing allowance; ensure that the cutting tool’s cutting edge is sufficiently sharp; and promptly select the correct measuring tools and adopt a reasonable measurement method for accurate measurements.

(6) Rough thread surface

If the cutting edge of the turning tool is not sharp enough, if an inappropriate cutting fluid is selected, if the cutting parameters are set incorrectly, if the wrong workpiece material is chosen, or if vibrations occur during the cutting process, the threaded surface will become rough and uneven. Solutions: Ensure that the cutting edge of the turning tool is sufficiently sharp; select an appropriate cutting fluid and use a suitable cutting speed; keep the feed rate as low as possible so that chips can be discharged perpendicularly to the axis; adjust all guide rail clearances to the minimum to minimize vibrations during cutting; and whenever possible, choose a tool holder with high rigidity, and when securing the tool holder, avoid extending it too far.

    3, Finally

Factors such as workpiece material issues, tool problems, and insufficient operator proficiency can all lead to machining problems on lathes. In the course of work, it’s essential to start from practical realities, employ various scientific and technical methods, carefully analyze and diagnose the root causes of these problems, identify the correct approaches to resolving them, and prevent similar issues from recurring in the future. repetition of Occur.