Motor and gearbox housings: coaxial bearing bores, pilots and sound metal

The bearing bores at each end must be closely coaxial and the pilot and mounting faces square to the axis, or running torque and noise rise and bearings wear early. The bosses carrying the bores are the heaviest, last-to-freeze sections, so shrinkage collects there and opens onto the bearing seat once fine boring removes the dense skin. The housings are built light and thin-walled, so clamping force and cutting heat also distort them during machining.

We squeeze-feed the bearing bosses and leave only 0.1–0.3 mm of stock on the casting so finishing stays inside the dense layer; bores and pilot are finished in one setup on a machining centre, roughing and finishing are separated to relieve stress, and coaxiality and squareness are checked on the CMM. Critical CNC dimensions can be held to ±0.005 mm at best, depending on the part's geometry and size. At DFM we agree with you which features the casting holds and which the machining holds.

Boring bores in one setup and holding their coaxiality is central to our other production parts too: an aluminum water pump housing holds its bearing and seal bores coaxial within φ0.05 mm at CPK ≥ 1.33, a twin throttle body keeps its two bores within 0.02 mm of each other, and a crankcase side cover has its bearing seat and joint face machined in the same operation.