Hydraulic cylinder drift on deep hole drilling machines causes the feed axis to move when it should stay in position. This drift can advance the drill into the bore when it should be retracting, causing tool damage, or it can let the spindle head sag during a tool change, making alignment impossible. I have debugged drift problems on machines ranging from small gun drills to large BTA systems with 10-ton feed forces. ...
The rotating union transfers coolant from the stationary supply line to the rotating spindle. It is one of the most common failure points on a deep hole drilling machine. A failed union causes pressure loss and coolant spray, and it can also cause mist to flood the work zone. In my experience, roughly 30% of unscheduled downtime on deep hole machines traces directly back to this component. Anatomy of a Rotating Union The union sits between the machine coolant manifold and the spindle shaft. Inside, a stationary housing holds the inlet port while a rotating shaft connects to the spindle bore. The two halves meet at a mechanical seal face. Standard designs use silicon carbide seal faces running against a carbon ring. In larger machines rated above 80 bar, I have seen tungsten carbide faces used instead. The shaft rotates with the spindle, so the seal must maintain contact pressure while the spindle runs at several thousand RPM. ...
Problem Description A coolant leak at 80 bar doesn’t stay small for long. I’ve seen a pinhole leak in a high-pressure hose grow to a 5 mm tear within 30 minutes of operation. The leak drops system pressure by 20-30 bar, chip evacuation stops, and the drill starts rubbing. In deep hole drilling, coolant pressure is everything — a leak that drops pressure by even 10 bar can turn a good bore into a scrap part. ...