Thread-Milling

Problem Description Threading deep holes presents problems that don’t exist in shallow holes. The depth amplifies every alignment issue, chip evacuation challenge, and tool deflection problem. I’ve scrapped expensive hydraulic cylinder bodies because a tap broke at 200 mm depth in a 250 mm deep M20 thread. The reclamation cost was nearly as much as the original part value. The three most common thread problems I encounter are tap breakage from trapped chips, poor thread fit from bore taper, and off-axis thread starts. Each has a different root cause and a different fix. Over time I have developed a systematic approach to diagnosing and solving these issues before they cause scrap. ...

Problem Description Threading deep holes is risky with conventional taps. A broken tap stuck at the bottom of a 300 mm deep bore means hours of EDM work or scrapping the part. I’ve had to reclaim several high-value hydraulic cylinder bodies after taps snapped at the bottom of M16 threads in 4140 steel. Each reclamation job cost more in labor than the original threading operation. The tap also has to reach the full thread depth, which means extended shanks that are prone to deflection. A standard tap stretched out on a 200 mm extension doesn’t track straight. The threads come out bell-mouthed or tapered, and the pitch diameter drifts along the hole length. I’ve measured 0.08 mm of pitch diameter variation in tapped deep holes versus 0.03 mm in thread-milled holes. ...