The Beicun Paidao lathe, with its structural advantage of "no turret and multi tool parallel layout", is widely used in the machining of small precision shaft parts. However, its unstable machining accuracy can directly lead to dimensional deviations and a decrease in surface smoothness of the parts. This type of malfunction needs to be accurately investigated from the four dimensions of tool, spindle, feed, and clamping based on the structural characteristics of the cutting lathe, and restored to accuracy stability through systematic adjustments.
1、 Tool system: direct influencing factors of precision fluctuations
The cutting tools of the lathe are directly fixed on the tool holder, and abnormal tool condition is a high-frequency cause of unstable accuracy. If the cutting edge of the tool is worn or chipped, it will cause uneven cutting force, resulting in "ripples" or size gradients on the machined surface; If the tool installation is offset (such as the height of the tool tip not coinciding with the spindle center), it will cause taper errors or tooth profile deviations (when machining threads).
When troubleshooting, it is necessary to first remove the cutting tool, check the blade status with a magnifying glass, and replace it in a timely manner when the wear exceeds the limit; When installing a new tool, calibrate the tool tip height with a dial gauge to ensure that the deviation from the spindle center is ≤ 0.01mm. At the same time, tighten the tool clamping bolt to prevent tool loosening during machining. In addition, insufficient rigidity of the blade holder can also cause vibration. It is necessary to check the connecting bolts between the blade holder and the bed. If they are loose, they need to be tightened again. If necessary, rigid pads should be added to enhance support.
2、 Spindle components: the core guarantee of precision benchmark
The spindle is the reference for the rotation of parts, and its radial runout and end face runout exceeding the tolerance will be directly transmitted to the machining accuracy. If there is bearing wear on the spindle of the Beicun cutting lathe, it will cause the rotation center of the spindle to shift, and the processed parts will have "ellipticity"; If the chuck at the front end of the spindle is worn or the clamping force is insufficient, it will cause the parts to move during cutting, leading to dimensional fluctuations.
When processing, it is necessary to first stop the machine to check the spindle accuracy: use a dial gauge to measure the head to contact the outer circle of the spindle clamp, manually rotate the spindle. If the radial runout is greater than 0.005mm, the spindle needs to be disassembled and replaced with high-precision angular contact ball bearings, and the bearing preload needs to be readjusted; If the clamp is worn, it is necessary to replace it with a clamp of the same model, or restore the accuracy by grinding the inner hole of the clamp. At the same time, check the clamping pressure (or oil pressure) of the clamp to ensure that the clamping force meets the processing requirements and avoid loosening of the parts.
3、 Feed transmission: a key link in motion accuracy
The X-axis and Z-axis feed of the cutting lathe directly determine the radial and axial dimensions of the parts. Excessive clearance in the feed system or wear of the transmission components can lead to "large dimensional repeat errors". If the clearance between the ball screw and the nut exceeds the standard, it will cause the tool holder to move with an "empty stroke"; Wear of the guide rail can cause the tool holder to move and jam, disrupting the cutting trajectory.
When troubleshooting, you can manually push the tool holder and feel if there is any obvious looseness: if the gap between the lead screw is too large, you need to adjust the pre tightening nut of the lead screw nut to eliminate the gap; If the guide rail is worn, it is necessary to clean the iron filings and oil stains on the surface of the guide rail, apply special guide rail lubricating oil, and repair minor scratches by manual grinding. In severe cases, the guide rail slider needs to be replaced. At the same time, check the coupling between the servo motor and the screw. If the bolts are loose, they need to be tightened again to ensure that there is no deviation in power transmission.
4、 Clamping and positioning: the foundation of accuracy consistency
Improper clamping and positioning of parts can lead to "scattered accuracy of batch parts". If there are impurities on the positioning reference surface of the spindle chuck, it will cause inaccurate centering of the parts during clamping; If long axis parts lack tailstock support, they will experience "bending deformation" during processing due to insufficient rigidity.
When solving the problem, it is necessary to clean the impurities in the inner hole of the clamp head and the end face of the part before each clamping to ensure a tight fit; When processing shaft parts with a length to diameter ratio greater than 5, it is necessary to use the top support of the tailstock and adjust the tightening force of the tailstock to avoid bending or movement of the parts. After the clamping is completed, use a dial gauge to check the radial runout of the parts and confirm that it is ≤ 0.008mm before starting the machining.
After the fault is resolved, 3-5 standard test pieces need to be processed to verify the accuracy. Key dimensions should be measured using calipers and micrometers to confirm that the error is stable within the allowable range. In daily maintenance, it is necessary to check the tool status and guide rail lubrication every week, calibrate the spindle accuracy every month, prevent unstable accuracy faults from the source, and ensure the precision machining capability of the Beicun cutting lathe.