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Bevel gears in SolidWorks, Fusion 360, Inventor and FreeCAD

Most CAD programs can draw a bevel gear blank, few can cut a correct bevel tooth. The quicker route is to design the pair, export it as STEP and bring the solids in. This guide shows what the files contain, where they sit in space, and how to open and mate them in SolidWorks, Fusion 360, Inventor and FreeCAD.

1. Export the pair

Design the pair in the bevel gear designer - straight or spiral - check the 3D preview, and press Generate STEP. Building the exact solids takes from about half a minute for a straight pair to a minute or two for a spiral one, and asks you to sign in with Google first, since each build is a heavy job on the server. The files then appear as downloads.

2. What the files contain

File	Contents	Use it for
`…_pinion.step`	The pinion as one solid, in its own frame	part drawing, CAM, analysis
`…_wheel.step`	The wheel as one solid, in its own frame	part drawing, CAM, analysis
`…_pair.step`	Both solids, already in mesh	checking the pair, a quick assembly
`….txt`	The dimension report, pinion and wheel	the drawing's dimensions, mounting distance
`….stl` (optional)	Triangle meshes of both members	3D printing, rendering

The STEP files are AP214 and in millimetres. The flanks are the generated tooth - octoid or spherical involute on a straight pair, the envelope of the face-mill cutter on a spiral pair - with the root fillet the cutter's edge leaves, and the backlash already taken out of the tooth thickness. Measured on a 20/40 straight and a 20/40 spiral pair file, the two solids do not overlap anywhere.

The solid model of a straight bevel pair, 20 and 40 teeth, in mesh — A straight 20/40 pair from the pair file, pinion and wheel in mesh.

3. Where the parts sit

Knowing the frame saves most of the work in an assembly:

Each member file has the pitch apex at the origin and the gear's axis along +Z: the gear lies on the positive side, its teeth facing back towards the apex, and the crown - the outer tip corner - sits at z = X, the "pitch apex to crown" mounting dimension in the text report.
In the pair file the pinion is left where it is, and the wheel is turned about its own axis so that a tooth space faces the pinion's tooth, then tilted by the shaft angle about the Y axis. For a 90° pair: pinion axis +Z, wheel axis +X, both apexes at the origin.
A straight pair carries the bore and hub you entered; a spiral pair's blank has no bore, so add it in CAD.

4. Opening a STEP file

Menu names shift a little between versions, but the route is the same everywhere: open the file as a STEP file and let the program convert it to its own part.

SolidWorks

File › Open, set the file type to STEP (*.step; *.stp) and pick the file. Each member comes in as a part with one body; the pair file as a part with two bodies or an assembly, depending on the import options.

Fusion 360

File › Open › Open from my computer, or upload the file to a project in the Data Panel. Fusion translates it in the cloud and opens it as a design with the bodies in it.

Autodesk Inventor

File › Open and choose STEP files, or use the CAD import command to reference the file. A member opens as a part; the pair file as a part with two bodies or an assembly, depending on the options.

FreeCAD

File › Open (or File › Import into an open document) and pick the .step file. The solids arrive as Part objects, ready for the Part, PartDesign or TechDraw workbenches.

5. Mating the pair in an assembly

For a quick look, open the pair file - it is already in mesh. To build your own assembly from the two member files:

Insert the pinion and fix it, or constrain its axis (the part's Z axis) to its shaft.
Insert the wheel and make its origin coincide with the pinion's: the two pitch apexes are the same point.
Set the angle between the two Z axes to the shaft angle - perpendicular for a 90° pair.
Turn the wheel about its own axis until a tooth space faces a pinion tooth; the pair file shows the right position.
To make them turn together, add the program's gear or motion constraint with the ratio z₁ : z₂ - a Gear mate in SolidWorks, a Motion constraint in Inventor, a Motion Link in Fusion 360.

On a real machine the mounting distance - pitch apex to crown - sets where each gear sits along its shaft. Build the shafts and shoulders from that dimension, not from the outside diameter.

6. After the import

Keep the scale at 1: the files are already in millimetres.
Add keyways, bores (on a spiral pair), holes and chamfers as features on the imported body; leave the teeth themselves alone.
For a drawing, the dimension report has the values a bevel gear drawing usually carries - pitch and outside diameters, angles, mounting distance, tooth depths and thickness.
For 3D printing, tick also write STL before generating, or export STL from your CAD program.

Design your pair and download it as STEP.

Open the designer

Questions

Which CAD programs can open the bevel gear files?

Any CAD program that imports STEP - SolidWorks, Inventor, Fusion 360, CATIA, NX, Creo, Solid Edge and FreeCAD among them. The files are STEP AP214, in millimetres.

Is the backlash included in the 3D model?

Yes. The normal backlash is taken out of the tooth thickness of both members, so the pair file's solids sit in mesh without overlapping.

Can I 3D print a generated bevel gear?

Yes. Tick 'also write STL' before generating to get meshes of both members, or export STL from your CAD program after importing the STEP files.

Are the teeth exact or an approximation?

They are the generated tooth: octoid or spherical involute flanks on a straight pair and the face-mill cutter's envelope on a spiral pair, with the root fillet the cutter leaves - not a profile drawn to look right.