Hole-Quality

Runout is one of those problems that is easy to ignore because the symptoms look like other issues. A hole comes out 0.03mm oversize and the natural instinct is to check the drill diameter or the bushing clearance. Half the time, the culprit is tool runout. Here is what I have learned about measuring runout, understanding its effects, and controlling it. What Runout Actually Does to the Hole When a gun drill has runout at the tip, the cutting edge orbits around the spindle centerline instead of rotating on-axis. This orbit increases the effective cutting diameter. ...

What Tool Runout Is and Why It Matters Tool runout is the amount by which the drill deviates from true rotation. Imagine a drill that is spinning on center but the tip is 0.02mm off to one side. That drill cuts a hole that is 0.02mm larger than the drill diameter at a minimum. I check tool runout as part of every setup, not just when problems appear. The check takes 30 seconds and tells me whether the tool is going to produce the correct hole size. It is the fastest quality check I can perform. ...

Machine rigidity is the foundation of deep hole drilling quality. You can have the best drill, the right parameters, and the perfect coolant setup, but if the machine isn’t rigid, the holes won’t be straight. I’ve worked on machines ranging from light-duty job shop gun drills to massive BTA production machines. The difference in rigidity shows up in every hole they produce. How Rigidity Affects the Hole A machine that lacks rigidity flexes under cutting forces. The flex causes: ...