Gearbox Housing

A gearbox housing carries two jobs at once: it has to hold bearing positions in a fixed relationship under load, and it has to keep lubricant inside and contamination outside. Both fail in the same place — at the bores and the joint faces — so that is where drawing review starts.

What a Gearbox Housing Has to Hold True in Service

The housing is the reference for everything mounted in it. Bearing bore diameter, bore-to-bore centre distance, and the perpendicularity of each bore to its sealing face decide how the gear train runs before any load is applied. A housing that machines cleanly but drifts on centre distance produces noise, heat and shortened bearing life, and none of that is visible until the unit is assembled and run.

Aluminium 6061, cast iron and fabricated steel each reach that geometry by a different route. Aluminium is chosen where weight and heat dissipation matter. Cast iron is chosen for damping and dimensional stability under varying temperature. A fabricated steel weldment is chosen when volumes are low, the design is still changing, or the shape does not justify a pattern. Machined faces need a flatness and roughness that a gasket or liquid sealant can work against; the specification on this page calls out Ra 1.6 on the machined surfaces.

Choices That Decide How a Gearbox Housing Gets Made

• Material route — cast, wrought aluminium or fabricated weldment. This sets the machining allowance, the datum scheme and whether stress relieving is needed before finishing.
• Datum and clamping — the faces used to locate the part in the fixture should be the same faces the drawing uses for its tolerances. If they are not, the machined result will be accurate to the fixture and wrong to the assembly.
• Sequence of heat treatment and finish machining — where heat treatment is applied, the roughing pass, the treatment and the finishing pass have to be planned as one sequence, not three independent operations.
• Wall thickness transitions — abrupt changes in section are where distortion shows up after welding and where a casting pulls during solidification.

These are the decisions worth settling before the first part is cut, because changing any of them after a fixture exists costs more than changing them on paper. Our DFM engineering review covers exactly this stage.

How Bore Geometry and Sealing Faces Are Verified

Inspection follows the buyer drawing and the approved sample. On a housing with a ±0.03 mm bore requirement, that means measuring the bore itself, the distance between bores, and the relationship of each bore to the face it seals against — not just checking diameter in isolation. Surface finish is verified on the specified faces. Material documentation is issued with the batch so the heat and the certificate can be traced; see material certification and traceability for how we handle that.

Where a finished unit has to meet a gear-industry standard, that rating and the associated type testing belong to the gearbox manufacturer or to the third-party body they nominate. Our scope is the housing as drawn: the geometry, the material and the surface condition stated on the drawing.

Can you hold ±0.03 mm on the bearing bores?

We machine to the tolerance the drawing states and inspect to it. What has to be settled in the drawing review is whether that figure applies to the bore alone or to the bore-to-bore relationship, because the second is a fixturing and datum question rather than a spindle capability question.

Cast, or fabricated and welded?

Both routes are open. Send the annual volume, the revision history of the design and the operating environment, and the comparison is made on total cost and lead behaviour rather than on unit price alone.

What do you need to quote?

The STEP or DWG geometry, the 2D drawing with tolerances and surface finish marked, the material, the quantity split between samples and batch, and the destination. Timing is quoted after drawing review and process confirmation.