The editor noticed that many friends new to mechanical processing find the drilling process in CNC machining of connecting rods particularly challenging—why is the precision always substandard? Why is the surface roughness unstable? In fact, although drilling is a common process, for high-demand small parts like connecting rods, achieving accurate and smooth drilling really requires quite a few techniques!  

 I. Why Is Connecting Rod Drilling So Important?  

The connecting rod is a core transmission component in an engine. The large and small holes on it connect the piston and crankshaft, which bear high loads and operate at high speeds. Therefore, the positional accuracy, dimensional consistency, and surface roughness of these holes must be strictly controlled. If the drilling is not done properly, it can easily lead to increased wear, abnormal noise, or even fracture... At that point, it will be more than just a matter of rework!  

Common problems include:  

- The hole is offset, making it impossible to install the shaft;  

- The hole diameter fluctuates (sometimes too large, sometimes too small), resulting in loose fits;  

- The hole wall has burrs or scratches, affecting service life.  

So, drilling is by no means as simple as "making a hole"!  

 II. Which Factors Affect Drilling Precision?  

In the editor’s opinion, the following aspects deserve key attention:  

1. Equipment and Cutting Tools: CNC drilling machines or machining centers must have good rigidity, and the radial runout of the spindle should not be excessive. For tools, the drill bit material (such as cemented carbide or coated drill bits) and the degree of cutting edge wear directly affect the results.  

2. Fixture Design: Connecting rods have irregular shapes. If clamping is unstable, they are prone to shaking or shifting during processing. A good fixture should provide reliable positioning and uniform clamping force, while also considering heat dissipation and chip removal.  

3. Cutting Parameters: The spindle speed, feed rate, and cooling method must be properly matched. For example, when processing steel connecting rods, excessively high speed may cause tool burning, while excessively low speed can easily lead to burrs.  

4. Material Properties: Connecting rods are usually made of 45 steel or alloy steel, which have relatively high hardness and sometimes require quenching and tempering first—the harder the material, the more important it is to control cutting force and temperature during drilling.  

 III. How to Ensure Drilling Precision? The Editor Shares Some Experiences!  

- Optimize Tool Selection and Replace Tools Regularly: The editor recommends using cemented carbide drill bits for small to medium-batch production; for large-batch production, coated drill bits can be used to extend service life! Do not continue using worn drill bits—replace or regrind them in a timely manner, otherwise, hole diameter deviation and roughness will definitely get out of control.  

- Ensure Stable Clamping and Accurate Positioning: Use dedicated fixtures as much as possible to firmly fix the large-end face or process boss of the connecting rod, reducing vibration! For connecting rods with thin-walled or complex structures, consider "one surface + two pins" positioning to restrict six degrees of freedom.  

- Do Not Copy Cutting Parameters Blindly: Cutting parameters need to be adjusted according to actual conditions. For example, when the editor processed connecting rods made of 40Cr material, setting the spindle speed to 1800-2200 rpm, feed rate to 0.12 mm/r, and matching with internal coolant achieved good results! It is recommended to first test-cut a few workpieces, measure the precision and surface finish, and then proceed with mass production.  

- Cooling and Chip Removal Are Key: Especially for deep-hole drilling, sufficient cooling is necessary to avoid thermal deformation! Remove chips in a timely manner to prevent scratches on the hole wall—the editor has seen some technicians use compressed air to assist in chip blowing, which works well.  

- First-Piece Inspection + Sampling Inspection Are Indispensable: During mass production, the first workpiece must undergo strict inspection for hole diameter and position accuracy! Conduct regular sampling inspections during the process to detect tool wear or equipment deviations in a timely manner.  

 IV. What to Do If Precision Problems Already Occur?  

Don’t panic! The editor provides several troubleshooting ideas:  

- Dimensional Deviation: First, check if the drill bit size is accurate and if the clamping is loose; then adjust the cutting parameters.  

- Hole Position Offset: This is mostly caused by wear of the fixture’s positioning components or improper clamping—inspect the fixture immediately!  

- Rough Surface: This may be due to a dull drill bit, insufficient cooling, or excessive feed rate—try reducing the feed rate and improving cooling.  

 V. Personal View: Connecting Rod Processing Will Become Smarter and More Efficient in the Future  

The editor believes that with the application of sensors and adaptive control technology, future CNC drilling processes will be able to monitor tool status and processing quality in real time, automatically adjust parameters—and even provide early warnings for faults! At the same time, with the popularization of multi-tasking machining centers and robotic loading/unloading, the efficiency and consistency of connecting rod drilling will be further improved.  

However, having said that, no matter how advanced the technology is, solid basic skills are still essential! The editor recommends that novice friends learn more about material properties, tool selection, and fixture principles—only in this way can they truly handle various on-site problems.  

Hope these experiences help you! If you have specific problems, feel free to leave a message and discuss together!