Spiral Bevel Gearbox Design

The brief

The customer needed a compact right-angle drive with defined input and output shaft positions, and wanted confidence in the internal layout before committing to a cast housing. Once a casting pattern exists, moving a bearing seat or a shaft centre is expensive, so the layout had to be right first time.

The drive arrangement

The gearbox turns drive through 90 degrees on intersecting shafts using a spiral bevel pair, whose curved oblique teeth engage progressively rather than all at once — the reason spiral bevel runs quieter and carries more load than a straight bevel of the same size. One shaft runs right through the housing and exits both sides; the mating shaft enters perpendicular to it. Both external shaft ends are splined, giving positive drive engagement without relying on a key.

Bearings, retention and sealing

Both shafts run on deep-groove ball bearings seated in dedicated housing bores, held by bearing retainers on socket head cap screws. The bevel gear is located axially by a castellated nut locked with a cotter pin — a deliberately old-fashioned choice, but one that will not vibrate loose and that a fitter can inspect at a glance. Rotary radial lip seals at each shaft exit keep oil in and contamination out.

The housing

The housing is a single cast and machined body with an open top face, drilled and tapped for a bolt-on cover so the gear set can be inspected without disturbing the shafts. Mounting feet are integrated into the casting rather than bolted on, and hex-head service plugs in the side and lower walls handle filling and draining. Section thicknesses carry the bearing loads through to the feet, since a housing that flexes lets the gear mesh wander.

The sectional view

The cutaway shown here is what the customer signed off on. It exposes the bearing arrangement on both shafts, the depth of the bevel mesh and how the wall thickness carries through to the mounting foot. Presenting a design this way removes most of the back-and-forth — the customer sees the mesh and the bearing spacing directly rather than inferring them from a table of dimensions.

What was delivered

A fully parametric SolidWorks assembly, a sectional general-arrangement drawing, individual part drawings for housing and shafts, and a bill of materials covering the bought-out bearings and seals. Because the model is parametric, a change in ratio or centre distance propagates through the drawings instead of requiring a redraw.