Chatter

Why Thin Wall Cylinders Vibrate Thin wall cylinders vibrate during deep hole drilling because the wall flexes under cutting forces. The ratio of bore diameter to wall thickness determines how susceptible a cylinder is to vibration. In my experience, cylinders with a diameter-to-wall-thickness ratio above 10:1 will vibrate under normal cutting conditions. When the cylinder wall flexes, the cutting tool encounters an inconsistent depth of cut. The drill digs in deeper when the wall deflects away, then cuts less when the wall springs back. This alternating force creates chatter marks on the bore surface and can chip the cutting edges of the drill in extreme cases. ...

Machine vibration during deep hole drilling causes chatter marks on the bore surface and reduces tool life. I have traced most vibration problems to three root causes: foundation issues, worn bearings or drive components, and workpiece resonance. Each cause produces a different vibration pattern, and identifying the pattern is the first step toward a fix. Vibration Diagnosis by Pattern I have learned to recognize vibration patterns by observing the chatter marks on the bore surface and feeling the machine during operation. The following table summarizes the patterns I have encountered and their most likely causes. ...

Thin wall stainless tubes are used in sanitary, pharmaceutical, and food processing applications. The wall thickness is often 3-6mm with a bore diameter of 25-60mm. The challenge is that the tube wall cannot support much cutting force without collapsing. I have drilled thousands of these tubes over the years and developed a specific approach that avoids the common failure modes. The applications I have worked on include dairy processing lines, pharmaceutical transfer tubes, brewery heat exchanger tubes, and clean-in-place manifolds. Each of these applications requires a smooth, crevice-free bore surface. Any surface defect in a sanitary tube becomes a bacteria harborage point. The drilling process has to produce a clean bore without marking the tube OD. ...

Surface finish defects in gun drilling are the most common reason for part rejection that I encounter. The bore surface must meet the specified roughness and be free of visible defects. When the finish is wrong, the part is scrap or needs rework. I have developed a systematic approach to identifying and fixing surface finish problems by looking at the defect pattern. Problem Description The surface finish of a gun-drilled bore depends on the tool condition, cutting parameters, coolant system, and machine rigidity. A defect in any of these areas shows up on the bore surface as a characteristic pattern. The pattern tells me which area to investigate. ...

How Vibration Affects Deep Hole Drilling Vibration is one of the most destructive forces in deep hole drilling. It leaves chatter marks on the bore surface, reduces tool life by 50% or more, and can break the drill in severe cases. The vibration energy that should go into cutting goes into the workpiece and the machine instead. I have seen parts scrapped from vibration damage that looked like the bore had been machined with a thread cutting tool. The chatter marks were 0.05mm deep and the surface finish was completely unacceptable. The part had 4 hours of machining invested before the final bore operation. ...