Fixing Misaligned Holes in a Steel Part2025-08-12

A client designed a low-carbon steel CNC machining part measuring 1500mm long, 19.05mm wide, and 38.1mm high. This door support guide component required five equally spaced countersunk holes to be drilled along the 19.05mm wide face, centered left to right. During first article inspection, it was discovered that the drilled holes were misaligned, compromising the part’s functionality and precision. Discussions between the QC and engineers team revealed that the root cause was insufficient fixturing during the drilling process:

The component was held in place using an inadequate number of vises, which failed to secure the long, slender part properly. The lack of sufficient clamping allowed the material to shift or flex during drilling, resulting in misaligned holes that deviated from the specified positions. This misalignment could affect the part’s assembly accuracy, structural integrity, and overall performance in its intended application.

  Fixing Misaligned Holes in a CNC Machining Steel Part  

Implemented Solution

To address the misalignment issue, the engineering team took the following corrective actions:

• Increased Vise Clamping: The number of vises used to secure the component was increased to four, strategically placed along the 1500mm length to provide robust and even clamping force. This ensured the part remained stable and rigid during drilling.
• Straightness Verification: Before drilling, a dial indicator was used to measure the straightness of the component, confirming it was within a tolerance of 0.1mm. This step ensured the part was properly aligned and free of deflection prior to machining.
• Redrilling Countersunk Holes: With the improved fixturing and verified straightness, the five countersunk holes were redrilled, achieving the required equal spacing and centered positioning on the 19.05mm face.

These adjustments resulted in accurately positioned holes that met the client’s specifications and passed QC inspection.

  Increased Vise Clamping and Straightness Verification  

Professional Machining Recommendations

To prevent similar issues in future projects and optimize the machining process, the following recommendations are proposed:

• Optimize Fixturing Design: For long, slender components like this one, use a minimum number of vises or custom fixtures to distribute clamping force evenly along the length. Ensure vises are positioned to minimize deflection, particularly near the drilling locations, and use soft jaws or padded clamps to avoid surface damage to the low-carbon steel.
• Pre-Machining Inspection: Always verify the straightness and flatness of the workpiece using precision tools like a dial indicator before machining. A tolerance of 0.1mm or better is recommended for high-precision applications.
• Tooling and Process Optimization: Use high-precision drilling tools with appropriate cutting parameters (e.g., feed rate and spindle speed) suited for low-carbon steel to minimize vibration and ensure clean cuts. Consider peck drilling for deep countersunk holes to reduce heat buildup and improve chip evacuation, further enhancing accuracy.
• Quality Control Enhancements: Implement in-process inspections using coordinate measuring machines (CMM) or laser scanning to verify hole positions during machining, catching potential misalignments early. Document fixturing setups and straightness measurements for traceability and to standardize processes for similar components.

Conclusion

The misalignment of countersunk holes in the 1500mm x 19.05mm x 38.1mm low-carbon steel CNC machining part was caused by insufficient vise clamping, allowing the part to shift during drilling. By increasing the number of vises, verifying straightness within 0.1mm, and redrilling the holes, the engineering team resolved the issue and delivered a part that met specifications. The proposed recommendations, including optimized fixturing, pre-machining inspections, and enhanced quality control, will help ensure precision and reliability in similar machining projects, preventing future drilling disasters and ensuring client satisfaction.