The turbocharger spins its shaft at hundreds of thousands of rpm, and every drop of its oil reaches the bearing through a handful of small, awkward holes — an inclined entry into the bearing bore, an intersection with a cored passage, an exit into a machined cavity. Each one is a gundrilling problem that the industry treats as genuinely hard. This page covers the geometry, the burr battle, and what separates a shop that struggles with turbo parts from one that quotes them.
A turbocharger bearing runs on a thin oil film that is constantly refreshed through small feed holes in the shaft and the bearing housing. The holes are small (a few millimetres at most), they enter at awkward angles, they cross cored passages cast into the housing, and they cannot leave a burr — a loose burr in a turbo bearing is a failure in seconds.
The classic turbo job: an oil feed hole drilled from the outside of the bearing housing or shaft, entering the bearing bore at an angle — commonly 10–40° to the axis. The inclined entry makes the drill start on a curved, sloping surface, which is where gundrilling demands a starting bushing or a prepared flat.
Turbo housings are cast, and the oil passages are cored in the casting — which means the machined feed hole must intersect a cast surface that was never machined. The drill crosses from clean metal into a rough, sometimes porous cast cavity, losing its guidance at the moment of intersection.
Every exit and every intersection in a turbo part leaves a burr, and the oil film cannot tolerate it. Deburring small internal holes is itself a specialty: the tool must reach the burr inside a few-millimetre hole at an angle.